Linaro-mm-sig

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116 participants
7230 discussions

by foltzbutman＠gmail.com

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1 week, 4 days

Re: [PATCH v5 0/9] vfio/pci: Add mmap() for DMABUFs

by Matt Evans

Hi David, On 16/07/2026 22:23, David Matlack wrote: > On 2026-07-16 03:51 PM, Matt Evans wrote: >> Hi David, >> >> On 15/07/2026 19:12, David Matlack wrote: >>> On Wed, Jul 15, 2026 at 10:47 AM Matt Evans <matt(a)ozlabs.org> wrote: >>> >>>> This is based on v7.2-rc3. >>>> >>>> These commits are on GitHub for easier browsing, along with >>>> "[RFC ONLY] selftests: vfio: Add standalone vfio_dmabuf_mmap_test": >>>> >>>> https://github.com/metamev/linux/compare/v7.2-rc3...dev/mev/vfio-dmabuf-mma… >>> >>> It'd be great to have this test upstream. I'm happy to review it when >>> you're ready. Looks like it just needs to be redone to use the VFIO >>> selftests library and kselftests harness. AI could probably do the >>> conversion pretty quick :) >> >> For sure, I'd intended to catch up with you on best approach here. :) >> >> Aside from the organic structure of the test (the open-coded VFIO >> device/group setup/init needs to go), the main issue is that it relies >> on a hacked/out of tree QEMU "EDU++" device with a second larger BAR >> (containing freely read-writable memory). A subset of tests run with >> the in-tree EDU device, but coverage is too low. >> >> The desirable properties are: >> >> - Having a BAR that is pure memory (all locations present, writable >> without disruptive side-effects) so that mapping aliases can be >> constructed and detected. This is good to test things like non-zero >> vm_pgoffs and VA space presentation of physically-discontiguous DMABUFs. >> >> - BAR >> hugepage size so we can eyeball huge mappings work (or better, >> mechanically test for them). At least 32MB would tick this box for 4K, >> 16K page systems. >> >> - Something QEMU supports*, so one can run the test in a VM/TCG system. >> >> There were some real device models in QEMU that could be used this way, >> but needed a fair bit of setup; I didn't want to rathole >> vfio_dmabuf_mmap_test on including a ton of device-specific code for >> some video card or similar. >> >> I'll dig more for a simple target that provides these properties -- >> obviously it would be better to point this test at an off-the-shelf >> device (including silicon!). And, proposing EDU extensions to the QEMU >> folks may be useful (there're uses for a better EDU in other contexts too). >> >> Since this test uses MMIO for a specific [class of] function, my first >> thought is it should be another VFIO driver-type test sibling of >> vfio_pci_driver_test. For example, we could extend the driver-type >> tests' backend struct vfio_pci_driver_ops for functions capable of >> providing a Big Memory BAR, like QEMU EDU++. EDU can also memcpy, so >> could also support vfio_pci_driver_test. >> >> The spirit of the device backends hiding setup of a complex device is >> handy, and it's plausible that several backends could provide this "big >> memory BAR" service. What do you think, any concerns with extending >> vfio_pci_driver_ops like that? > > I wouldn't recommend leveraging the driver framework unless absolutely > necessary. It makes the test harder to run. > > The biggest issue I see with the proposed properties is being able to > treat the BAR as memory. That obviously will depend on the device and > may require device-specific setup. If we decide that treating the BAR as > memory is truly required then using the driver framework is the way to > go. But I'm hoping we can avoid that requirement. > > Instead, I think you can get pretty far by inspecting /proc/pid/pagemap > to determine if the mmap() set things up correctly, without actually > accessing the BAR. You can use /proc/pid/pagemap to look up the PFN and > PAGEMAP_SCAN to detect huge pages. Hmm, possible, although that's quite a different test at that point. I agree never touching the device has advantages, but it's harder to test certain things if we _never_ do MMIO. The mitigation effort to get coverage may not be the right tradeoff vs easier running. I can think of some "easy" VFIO bugs that would be challenging to properly verify in userspace (e.g. PFNs all having some undesired offset). The current test method is harder to fool per unit effort in writing it. Though, I will have a think about this no-touch flavour of test. What were you picturing regarding populating the VMA PTEs in order to inspect the result via /proc/pid/pagemap, whilst still upholding the principle of not touching the device? For example, madvise(MADV_POPULATE_WRITE) won't work on the VFIO BAR regions because they're VM_PFNMAP/VM_IO. > With that requirement gone, then all you really need is a device with a > large enough BAR. And even that it not a hard requirement. I'm sure > there are plenty of test cases that could work with smaller BARs. The > few tests that want to exercise huge mappings can inspect the device BAR > sizes first, and if they're all too small, SKIP() the test. > > If you structure the test this way, then it's easy for the test to be > used. It can be run against any device for the basic functional > coverage, and can be run against a device with a larger BAR for full > coverage of huge mappings. > > Does QEMU emulate any devices that have 32MB or larger BARs? Yep, looks like `-device pci-testdev,membar=64M,membar-backed=on` or even `-device bochs-display,vgamem=64M` would be suitable. So I'll also try moving the existing test over to one of these to at least remove the EDU++ device dependency. (bochs-display has >1 BAR, and some MMIO regs which are nice for a quick kick-the-tyres access test.) Cheers, Matt

1 week, 4 days

A Beginner’s Guide to Enjoying Fnaf: Why This Horror Game Still Feels So Tense

by acute.hummingbird.ljmk＠hidepost.net

https://fivenightsatfreddysgame.io/ Introduction Horror games come in many forms. Some rely on monsters chasing you through dark hallways, while others create fear by making you feel trapped and helpless. One of the most famous examples of the second approach is Fnaf, short for Five Nights at Freddy’s. What makes the game interesting is that you don’t spend most of your time running around. Instead, you sit in a small security office, watching cameras and trying to survive until morning. The idea sounds simple at first, but the tension builds surprisingly fast. Every sound becomes suspicious, every camera check feels important, and every mistake can end the night immediately. For players who are new to horror games, Fnaf is a great example of how atmosphere and anticipation can be more frightening than constant action. Gameplay: What You Actually Do The basic setup is easy to understand. You play as a night security guard working at a family entertainment restaurant filled with animatronic characters. During the day they entertain guests, but at night they begin moving around the building. Your goal is straightforward: survive from midnight until 6 AM. To do that, you have a few tools: • Security cameras • Door controls • Hallway lights • Limited electrical power Most of the gameplay revolves around monitoring the cameras to track where the animatronics are located. If one gets too close to your office, you may need to close a door or check a hallway light. The problem is that every action consumes power, and once the power runs out, your defenses become much weaker. This creates the game’s main challenge: balancing information and resources. Check the cameras too often and you waste power. Ignore them for too long and an animatronic may reach your office without warning. That constant trade-off is what keeps the game tense even after you understand the rules. Why Fnaf Feels Different From Other Horror Games Many horror games focus on exploration, puzzles, or combat. Fnaf takes a much more restricted approach. You’re mostly sitting in one room. Surprisingly, that limitation makes the experience more intense. Because you can’t freely escape danger, you’re forced to pay attention to small details: • Footsteps • Mechanical noises • Camera movement • Sudden silence • Flickering lights The fear comes from anticipation rather than action. You know something is moving toward you, but you’re never completely sure when it will arrive. Another reason the game became so popular is its memorable characters. The animatronics are designed to look friendly on the surface, yet they become unsettling the longer you watch them. That contrast between a cheerful restaurant and a threatening nighttime atmosphere creates a unique style of horror. Tips for New Players If you’re trying Fnaf for the first time, the early nights can feel overwhelming. Here are a few simple tips that helped many players, including me, enjoy the game more. 1. Stay Calm The game is designed to make you panic. When something suddenly appears near your office, it’s easy to start clicking buttons randomly. Taking a breath and reacting carefully usually works better. 2. Learn the Camera Layout Spend a little time memorizing where the important rooms are located. Knowing which cameras connect to your office helps you react faster when animatronics begin moving. 3. Don’t Overuse the Doors A common beginner mistake is keeping the doors closed all the time. This drains power quickly. Use them only when an animatronic is actually nearby. 4. Listen Carefully Sound is extremely important. Headphones can make a big difference because audio cues often tell you more than the cameras do. 5. Expect a Few Jump Scares Everyone gets surprised at first. Instead of trying to avoid every jump scare, treat them as part of the learning process. After a few attempts, you’ll start recognizing the warning signs earlier. 6. Take Breaks if Needed Fnaf can be surprisingly stressful, especially during later nights. If your heart is racing after a tough attempt, there’s nothing wrong with taking a short break before trying again. The Best Way to Experience It In my opinion, Fnaf is most enjoyable when played in a quiet room with headphones and minimal distractions. The game relies heavily on atmosphere, so playing while multitasking removes much of the tension. I also recommend going into the game without watching too many strategy videos first. Discovering how the animatronics behave on your own makes the experience much more memorable. Part of the fun is slowly understanding the patterns and improving night by night. Playing with friends nearby can be entertaining too. Even people who aren’t controlling the game often react strongly to the sudden scares and close calls. Conclusion Fnaf remains one of the most recognizable horror games because it proves that a simple idea can create incredible tension. You don’t need complicated controls, huge maps, or constant combat to feel nervous. Sometimes sitting alone in a small office with limited power is enough. The game rewards observation, patience, and resource management while delivering plenty of suspense along the way. Whether you’re completely new to horror games or just looking for a classic experience, Fnaf offers a unique mix of strategy and fear that still holds up years later. If you decide to try it, don’t worry about surviving every night immediately. The fun comes from learning the patterns, reacting under pressure, and slowly becoming more confident as the nights get harder. That gradual progression is what makes the experience so memorable.

1 week, 4 days

Re: [PATCH v5 0/9] vfio/pci: Add mmap() for DMABUFs

by David Laight

On Thu, 16 Jul 2026 21:23:22 +0000 David Matlack <dmatlack(a)google.com> wrote: > On 2026-07-16 03:51 PM, Matt Evans wrote: > > Hi David, > > > > On 15/07/2026 19:12, David Matlack wrote: > > > On Wed, Jul 15, 2026 at 10:47 AM Matt Evans <matt(a)ozlabs.org> wrote: > > > > > >> This is based on v7.2-rc3. > > >> > > >> These commits are on GitHub for easier browsing, along with > > >> "[RFC ONLY] selftests: vfio: Add standalone vfio_dmabuf_mmap_test": > > >> > > >> https://github.com/metamev/linux/compare/v7.2-rc3...dev/mev/vfio-dmabuf-mma… > > > > > > It'd be great to have this test upstream. I'm happy to review it when > > > you're ready. Looks like it just needs to be redone to use the VFIO > > > selftests library and kselftests harness. AI could probably do the > > > conversion pretty quick :) > > > > For sure, I'd intended to catch up with you on best approach here. :) > > > > Aside from the organic structure of the test (the open-coded VFIO > > device/group setup/init needs to go), the main issue is that it relies > > on a hacked/out of tree QEMU "EDU++" device with a second larger BAR > > (containing freely read-writable memory). A subset of tests run with > > the in-tree EDU device, but coverage is too low. > > > > The desirable properties are: > > > > - Having a BAR that is pure memory (all locations present, writable > > without disruptive side-effects) so that mapping aliases can be > > constructed and detected. This is good to test things like non-zero > > vm_pgoffs and VA space presentation of physically-discontiguous DMABUFs. > > > > - BAR >> hugepage size so we can eyeball huge mappings work (or better, > > mechanically test for them). At least 32MB would tick this box for 4K, > > 16K page systems. > > > > - Something QEMU supports*, so one can run the test in a VM/TCG system. > > > > There were some real device models in QEMU that could be used this way, > > but needed a fair bit of setup; I didn't want to rathole > > vfio_dmabuf_mmap_test on including a ton of device-specific code for > > some video card or similar. > > > > I'll dig more for a simple target that provides these properties -- > > obviously it would be better to point this test at an off-the-shelf > > device (including silicon!). And, proposing EDU extensions to the QEMU > > folks may be useful (there're uses for a better EDU in other contexts too). > > > > Since this test uses MMIO for a specific [class of] function, my first > > thought is it should be another VFIO driver-type test sibling of > > vfio_pci_driver_test. For example, we could extend the driver-type > > tests' backend struct vfio_pci_driver_ops for functions capable of > > providing a Big Memory BAR, like QEMU EDU++. EDU can also memcpy, so > > could also support vfio_pci_driver_test. > > > > The spirit of the device backends hiding setup of a complex device is > > handy, and it's plausible that several backends could provide this "big > > memory BAR" service. What do you think, any concerns with extending > > vfio_pci_driver_ops like that? > > I wouldn't recommend leveraging the driver framework unless absolutely > necessary. It makes the test harder to run. > > The biggest issue I see with the proposed properties is being able to > treat the BAR as memory. That obviously will depend on the device and > may require device-specific setup. If we decide that treating the BAR as > memory is truly required then using the driver framework is the way to > go. But I'm hoping we can avoid that requirement. Could you run a test where only a known part of the BAR can be treated as memory? A large BAR is likely to have some areas that can be accessed as memory. David > > Instead, I think you can get pretty far by inspecting /proc/pid/pagemap > to determine if the mmap() set things up correctly, without actually > accessing the BAR. You can use /proc/pid/pagemap to look up the PFN and > PAGEMAP_SCAN to detect huge pages. > > With that requirement gone, then all you really need is a device with a > large enough BAR. And even that it not a hard requirement. I'm sure > there are plenty of test cases that could work with smaller BARs. The > few tests that want to exercise huge mappings can inspect the device BAR > sizes first, and if they're all too small, SKIP() the test. > > If you structure the test this way, then it's easy for the test to be > used. It can be run against any device for the basic functional > coverage, and can be run against a device with a larger BAR for full > coverage of huge mappings. > > Does QEMU emulate any devices that have 32MB or larger BARs? >

1 week, 4 days

Brand Awareness: Unlock the Power of Robust Wiki Profile

by cameronluka9＠gmail.com

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1 week, 5 days

Venting Safely: A Look at the Joyfully Destructive World of Kick the Buddy

by happy.peafowl.mbed＠hidepost.net

We all have those moments, don't we? A frustrating day at work, a challenging interaction, or simply a build-up of everyday annoyances. Sometimes, you just need a healthy outlet to release that pent-up energy without actually harming anyone or anything important. That's where games like kick the buddy step in, offering a uniquely satisfying and surprisingly cathartic experience. Far from being just mindless destruction, these digital stress-relievers provide a humorous and accessible way to blow off steam. https://kickthebuddy.lol/ For those unfamiliar, Kick the Buddy is a mobile and web-based game centered around a simple, yet endlessly entertaining premise: you get to virtually abuse a ragdoll character named Buddy in a multitude of creative and over-the-top ways. It’s the kind of game that doesn't take itself seriously, and that's precisely its charm. It's not about intricate storylines or strategic battles; it's about pure, unadulterated, and consequence-free catharsis. The Gameplay Loop: A Symphony of Destruction The core gameplay of Kick the Buddy is refreshingly straightforward. Upon starting the game, you're presented with Buddy, a perpetually cheerful (or perhaps just oblivious) ragdoll, usually standing in the center of a room. Your objective? To unleash your inner destructive tendencies upon him using a vast arsenal of weapons and gadgets. The controls are intuitive and designed for touchscreens, making it incredibly easy to pick up and play. You simply tap and drag to throw Buddy around, or tap on weapons from a side menu to deploy them. The initial weapons are usually simple – a basic pistol, a baseball bat, or perhaps some throwing knives. As you play and earn in-game currency (often through the sheer volume of damage you inflict), you unlock more outlandish and elaborate tools of destruction. And this is where the game truly shines. The variety of ways you can "punish" Buddy is genuinely impressive and often hilarious. Want to pepper him with machine gun fire? Go for it. Feel like freezing him solid and then smashing him with a sledgehammer? Absolutely. Fancy launching him into space with a rocket launcher or calling down an airstrike? All within the realm of possibility. There are even more esoteric options like black holes, elemental attacks, and bizarre, fantastical devices that defy easy categorization. Each weapon has its own unique animation and sound effect, adding to the satisfying feedback loop. Beyond simply using weapons, you can also interact with Buddy directly. Drag him, spin him, bounce him off the walls – the physics engine, while not hyper-realistic, is good enough to make these interactions feel dynamic and engaging. There are also environmental hazards that can be triggered, like spikes emerging from the floor or laser grids. The goal is to inflict as much damage as possible, which then translates into the in-game currency you use to unlock more fun ways to inflict damage. It's a self-perpetuating cycle of gleeful destruction. You can experience this stress-relieving fun for yourself by checking out the official game at Kick the Buddy. Tips for Maximizing Your Mayhem (and Your Stress Relief) While "Kick the Buddy" might seem like a game where you can just randomly tap and destroy, a few tips can enhance your experience and make your stress-relief sessions even more effective: Experiment with Your Arsenal: Don't stick to just one or two weapons. The joy of the game comes from discovering new and increasingly outlandish ways to "kick" Buddy. Try combining different attacks – freeze him, then hit him with a rocket, then electrocute him. The creative possibilities are endless. Focus on Combos: Many weapons work well in conjunction with others. For instance, weapons that pin Buddy down (like a net) can set him up perfectly for more powerful, slower-acting weapons. Similarly, explosive weapons can launch him into environmental hazards for bonus points. Embrace the Absurdity: The game is meant to be silly. Don't overthink it. The more you lean into the over-the-top nature of the destruction, the more enjoyable it becomes. Laugh at the ridiculous sound effects and Buddy's enduring resilience. Utilize the Environment: Keep an eye out for interactive elements in the background. Sometimes, there are buttons or levers that can trigger unique hazards or effects, adding another layer of destructive fun. Don't Rush: While it's tempting to just spam weapons, take a moment to appreciate the animations and the effects. Sometimes, the most satisfying moments come from a perfectly timed, powerful attack. Consider Customization: As you progress, you'll often unlock options to customize Buddy's appearance or the background. While purely cosmetic, these can add a fresh feel to your destructive escapades. Conclusion: A Digital Punching Bag for the Soul "Kick the Buddy" and similar games offer a unique and genuinely beneficial form of entertainment. They provide a safe, consequence-free space to vent frustrations, unleash a little harmless aggression, and simply de-stress. It's a reminder that sometimes, the most effective way to deal with the pressures of life is to simply embrace a little absurdity and blow off some steam, even if it's just by virtually pelting a cheerful ragdoll with a barrage of rockets and lasers. So, the next time you feel a bit overwhelmed, consider giving Buddy a friendly (or not-so-friendly) visit – your sanity might just thank you for it.

1 week, 5 days

[PATCH 0/5] drm/sched: Introduce the miracle of locking to entity

by Philipp Stanner

Both Tvrtko [1] and I [2] have recently proposed some improvals for drm_sched. While taking Tvrtko's feedback into account for my patch, I realized that both his and my patch can be fully replaced with a bigger and far more beautiful series. If I am not mistaken, it turns out that the entire entity->entity_idle completion is also nothing but a workaround around the grave mistake of not using the greatest helper with parallel programming that exists in computer science: Locking. This series adds locking to the last_scheduled field and all checks related to detect the idleness of the entity. As before, the job_scheduled event queue causes the periodic checks. This way, we can get rid of memory barriers, RCU, a few lines of code, make things more readable, understandable... Tested with drm-sched-unit tests. I'm a bit busy right now, but wanted to show you guys the idea. Before merging I'd test it more exhaustively with Nouveau. Greetings, Philipp [1] https://lore.kernel.org/dri-devel/20260611123423.39819-1-tvrtko.ursulin@iga… [2] https://lore.kernel.org/dri-devel/20260626081942.2122144-2-phasta@kernel.or… Philipp Stanner (5): drm/sched: Protect entity->last_scheduled with spinlock drm/sched: Lock spsc_queue in drm_sched_entity_pop_job() drm/sched: Avoid lock cycle for sched_entity drm/sched: Lock drm_sched_entity_is_idle() drm/sched: Remove entity->entity_idle drivers/gpu/drm/scheduler/sched_entity.c | 75 +++++++++++------------- drivers/gpu/drm/scheduler/sched_main.c | 2 - drivers/gpu/drm/scheduler/sched_rq.c | 5 +- include/drm/gpu_scheduler.h | 16 ++--- 4 files changed, 41 insertions(+), 57 deletions(-) base-commit: be4f10d44757211fd656fa57f37034657f26c883 -- 2.54.0

1 week, 5 days

[PATCH v3 0/2] dma-buf: fix fd leak when copy_to_user() fails after fd_install()

by Baineng Shou

Several drivers call dma_buf_fd() — which internally calls fd_install() — before copy_to_user() returns the fd number to userspace. If copy_to_user() fails, the fd is already published in the caller's fd table but the ioctl returns an error, so userspace never learns the fd number. Worse, the window between fd_install() and copy_to_user() allows other threads to observe and manipulate the fd (dup, close, SCM_RIGHTS), making any "close it on the failure path" fix unsafe. The fix is to split the allocation into three steps: reserve an fd with get_unused_fd_flags() (not yet visible to other threads), do copy_to_user(), and only then publish the fd with fd_install() via the new dma_buf_fd_install() helper. On copy_to_user() failure, put_unused_fd() + dma_buf_put() cleanly unwind with no user-visible side effects. Patch 1 introduces dma_buf_fd_install() in dma-buf.c (wrapping fd_install() together with the DMA_BUF_TRACE call to preserve export tracing) and applies the fix to dma-heap. Patch 2 applies the same fix to fastrpc, which even had a comment acknowledging the problem could not be fixed before. v1: https://lore.kernel.org/dri-devel/20260703080922.1838362-1-shoubaineng@gmai… v2: https://lore.kernel.org/dri-devel/20260710105430.3059661-1-shoubaineng@gmai… Changes in v3: - Split into two patches (dma-heap + fastrpc separately) - Add dma_buf_fd_install() to preserve trace_dma_buf_fd tracepoint (spotted by T.J. Mercier and sashiko-bot on v2) - Add fastrpc fix using the new helper (suggested by T.J. Mercier) Baineng Shou (2): dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds misc: fastrpc: don't publish fd before copy_to_user() succeeds drivers/dma-buf/dma-buf.c | 20 ++++++++++ drivers/dma-buf/dma-heap.c | 80 +++++++++++++++++++------------------- drivers/misc/fastrpc.c | 16 +++----- include/linux/dma-buf.h | 1 + 4 files changed, 67 insertions(+), 50 deletions(-) -- 2.34.1

1 week, 6 days

[PATCH v5 0/5] rust / dma_buf: Add abstractions for dma_fence

by Philipp Stanner

Changes since v4: - Fix an uninitialized memory bug for FenceCbRegistration with ManuallyDrop. - Return FenceCtx as impl PinInit - Make FenceCtx return an impl PinInit<T, Error> (Danilo) - Reformat some comments - Adjust the docu for rcu_barrier(), so that it matches the C side's docu and our docu for rcu::synchronize_rcu(). Changes since v3: - Add a FIXME for an encountered Rust compiler bug. (Gary) - Add new Rust files also to DRM drivers & common infrastructure MAINTAINERS file. (Danilo) - Reposition ECANCELED error code. (Miguel) - Replace refcounted FenceCtx in DriverFenceData with a reference plus life time. (Boris) - Re-add rcu_barrier() patch, since we now can use it for dropping the fence context. (Danilo) - Add forgotten R-b from Alice, and Acks for MAINTAINERS from Christian and Sumit. Changes since v2: - Don't drop DriverFenceData as a whole, but only the members we really want to drop. Gives more robustness. (Gary). - Break apart large pin_init_from_closure(). (Danilo, Onur) - Remove rcu_barrier() and synchronize_rcu() from FenceCtx::drop(). FenceCtx might drop in atomic context, where you must not perform those operations. With the current way C dma_fence is designed, the driver must wait for a grace period manually until it unloads. - Repair the DriverFenceBorrow implementation, properly injecting a life time into it. (Danilo) - Fix memory layout bug for rcu_head. (Onur) - Drop RCU patches, since this series doesn't need them anymore. Changes since v1: - Remove unnecessary mutable references (Alice) - Split up unsafe comments where possible (Danilo) - Remove PhantomData + implement FenceCtx ops trait (Boris) - Consistently call FenceCtx generic data `T`. FenceDataType is derived from that. (Boris) - Add abstractions for call_rcu() and synchronize_rcu() (Danilo) - Add ECANCELED error code in Rust (Alice) - Remove the rcu_barrier() from FenceCtx::drop() – because we now use call_rcu(), there can be no UAF access to the FenceCtx anymore. In any case, it is illegal to use either call_rcu() or synchronize_rcu() in FenceCtx::drop(), because our new drop_driver_fence_data() can run in atomic context and might put the last fence_ctx reference. So we now only have to guard against module unload, which it seems either the driver or Rust driver-core / module unload infrastructure must solve. - Minor formatting etc. changes - Add C helpers to MAINTAINERS. (Danilo) - Ensure that `Fence::is_signaled()` is fully synchronized, i.e., all callbacks really have run. See [1] and [2]. (Myself, Christian König) Changes since the RFCs: - Include support for ForeignOwnable for ARef, so that a Fence can be stuffed into an XArray et al. (Code by Danilo) - Implement ForeignOwnable (with new borrow type) for DriverFence, so that it can be stuffed into an XArray. - Include the rcu::RcuBox data type to defer dropping data with RCU (Cody by Alice) - Port DmaFence to RcuBox to make UAF bugs through later, new dma_fence callbacks (backend_ops) impossible. - Force users to pass their fence data in an RcuBox (or have it not need drop()) through a Sealed trait. - Document the rules for the user's DriverFence::data's drop implementation very clearly (deadlock danger). - rustfmt, Clippy. - Various style suggestions, safety comments, etc. (Önur) - Add __rust_helper prefix to helper functions. (Önur) Changes in RFC v3: - Omit JobQueue patches for now - Completely redesign the memory layout: Instead of a Fence refcounting a DriverFence, both now live in the same allocation to allow for future support the dma_fence backend_ops callbacks which need to do container_of. (mostly Boris's feedback) - Allow for pre-allocating fences to avoid deadlocks when submitting jobs to a GPU. (Boris) - Simultaneously, allow for pre-preparing fence callback objects, so the driver can allocate them when it sees fit. (code largely stolen and inspired by Daniel). - Signal fences on drop, ensure synchronization. - Force users to set an error code when signalling. - Write more documentation - A ton of minor other changes. [1] https://lore.kernel.org/dri-devel/20260608142436.265820-2-phasta@kernel.org/ [2] https://lore.kernel.org/dri-devel/20260612104251.2264707-2-phasta@kernel.or… Alright, so since the last RFCs did not reveal significant design issues, I decided to transition this series to a v1 and hope that we can get it upstream. This now includes code for more common infrastructure that dma_fence needs, contributed by Danilo and Alice. --- Old cover letter for RFC: So, this is the spiritual successor of the first / second RFC [1]. v2 also contained code for drm::JobQueue, but mostly to show how the fence code would be used. JobQueue is under heavy rework right now, so I don't want to bother your eyes with it. The docstring examples should show how Rust fences are supposed to be used, though. This v3 contains a huge amount of highly valuable feedback from a variety of people, notably Boris, but also from Alice, Gary and Danilo. There are some TODOs open (a better trait for fence backend_ops and RCU support), but my hope is that this effort is now finally approaching its end. I would greatly appreciate feedback and especially more information about what might be missing to make this usable, which is obviously where Daniel's and Boris's feedback will be valuable once more. Please regard this patch just as what it's titled: an RFC, to discuss a bit more and to inform a broader community about what the current state is and where this is heading at. Many regards, Philipp [1] https://lore.kernel.org/rust-for-linux/20260203081403.68733-2-phasta@kernel… Danilo Krummrich (1): rust: types: implement ForeignOwnable for ARef<T> Philipp Stanner (4): rust: error: Add ECANCELED error code rust: sync: Add abstraction for rcu_barrier() rust: Add dma_fence abstractions MAINTAINERS: Add entry for Rust dma-buf MAINTAINERS | 5 + rust/bindings/bindings_helper.h | 1 + rust/helpers/dma_fence.c | 48 ++ rust/helpers/helpers.c | 1 + rust/kernel/dma_buf/dma_fence.rs | 894 +++++++++++++++++++++++++++++++ rust/kernel/dma_buf/mod.rs | 14 + rust/kernel/error.rs | 1 + rust/kernel/lib.rs | 1 + rust/kernel/sync/aref.rs | 40 ++ rust/kernel/sync/rcu.rs | 20 + 10 files changed, 1025 insertions(+) create mode 100644 rust/helpers/dma_fence.c create mode 100644 rust/kernel/dma_buf/dma_fence.rs create mode 100644 rust/kernel/dma_buf/mod.rs base-commit: a73a398a68ca9b9e5116a617562471f16b8310c4 -- 2.54.0

1 week, 6 days

[PATCH V5] i2c: qcom-geni: Add dynamic transfer timeout based on transfer length and frequency

by Aniket Randive

The driver uses a static XFER_TIMEOUT of HZ (1 second) for all transfers regardless of message length or bus frequency, causing unnecessary delays on error paths. Compute the timeout dynamically from message length and bus frequency with a 10x safety margin over the theoretical wire time. Add a 300 ms floor to account for I2C clock stretching and other situations where a slave may keep SCL asserted for an extended period, including faulty devices holding the bus. This replaces the fixed 1-second timeout with a transfer-specific timeout while preserving sufficient margin for software overheads and bus-level delays. For GPI multi-descriptor transfers, use the maximum message length across all queued messages as the per-completion timeout. Signed-off-by: Aniket Randive <aniket.randive(a)oss.qualcomm.com> --- Changes in V5: - Updated the commit message as per the review comments. Changes in V4: - As per konrad suggestion used mult_frac() for bit_usec to avoid intermediate overflow on 32-bit targets. - Updated the commit message and added a driver comment explaining the rationale for the 0.3-second minimum timeout floor value. drivers/i2c/busses/i2c-qcom-geni.c | 47 +++++++++++++++++++++++------- 1 file changed, 37 insertions(+), 10 deletions(-) diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c index 96dbf04138be..f011d2564cd2 100644 --- a/drivers/i2c/busses/i2c-qcom-geni.c +++ b/drivers/i2c/busses/i2c-qcom-geni.c @@ -74,9 +74,14 @@ enum geni_i2c_err_code { #define PACKING_BYTES_PW 4 #define ABORT_TIMEOUT HZ -#define XFER_TIMEOUT HZ #define RST_TIMEOUT HZ +/* 9 bits per byte (8 data + 1 ACK), 10x safety margin */ +#define I2C_TIMEOUT_SAFETY_COEFFICIENT 10 + +/* 300ms floor: budget for clock stretching; slave may hold SCL low indefinitely */ +#define I2C_TIMEOUT_MIN_USEC 300000 + struct geni_i2c_desc { bool no_dma_support; unsigned int tx_fifo_depth; @@ -204,6 +209,16 @@ static int geni_i2c_clk_map_idx(struct geni_i2c_dev *gi2c) return -EINVAL; } +static unsigned long geni_i2c_xfer_timeout(struct geni_i2c_dev *gi2c, size_t len) +{ + size_t bit_cnt = len * 9; + size_t bit_usec = mult_frac(bit_cnt, USEC_PER_SEC, gi2c->clk_freq_out); + size_t xfer_max_usec = (bit_usec * I2C_TIMEOUT_SAFETY_COEFFICIENT) + + I2C_TIMEOUT_MIN_USEC; + + return usecs_to_jiffies(xfer_max_usec); +} + static int qcom_geni_i2c_conf(struct geni_se *se, unsigned long freq) { struct geni_i2c_dev *gi2c = dev_get_drvdata(se->dev); @@ -445,7 +460,7 @@ static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg, u32 m_param) { dma_addr_t rx_dma = 0; - unsigned long time_left; + unsigned long time_left, timeout; void *dma_buf; struct geni_se *se = &gi2c->se; size_t len = msg->len; @@ -470,8 +485,9 @@ static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg, gi2c->dma_buf = dma_buf; } + timeout = geni_i2c_xfer_timeout(gi2c, len); cur = gi2c->cur; - time_left = wait_for_completion_timeout(&gi2c->done, XFER_TIMEOUT); + time_left = wait_for_completion_timeout(&gi2c->done, timeout); if (!time_left) geni_i2c_abort_xfer(gi2c); @@ -484,7 +500,7 @@ static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg, u32 m_param) { dma_addr_t tx_dma = 0; - unsigned long time_left; + unsigned long time_left, timeout; void *dma_buf; struct geni_se *se = &gi2c->se; size_t len = msg->len; @@ -512,8 +528,9 @@ static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg, if (!dma_buf) /* Get FIFO IRQ */ writel_relaxed(1, se->base + SE_GENI_TX_WATERMARK_REG); + timeout = geni_i2c_xfer_timeout(gi2c, len); cur = gi2c->cur; - time_left = wait_for_completion_timeout(&gi2c->done, XFER_TIMEOUT); + time_left = wait_for_completion_timeout(&gi2c->done, timeout); if (!time_left) geni_i2c_abort_xfer(gi2c); @@ -591,7 +608,7 @@ static void geni_i2c_gpi_multi_desc_unmap(struct geni_i2c_dev *gi2c, struct i2c_ * geni_i2c_gpi_multi_xfer_timeout_handler() - Handles multi message transfer timeout * @dev: Pointer to the corresponding dev node * @multi_xfer: Pointer to the geni_i2c_gpi_multi_desc_xfer - * @transfer_timeout_msecs: Timeout value in milliseconds + * @transfer_timeout_msecs: Per-message completion timeout in jiffies * @transfer_comp: Completion object of the transfer * * This function waits for the completion of each processed transfer messages @@ -601,7 +618,7 @@ static void geni_i2c_gpi_multi_desc_unmap(struct geni_i2c_dev *gi2c, struct i2c_ */ static int geni_i2c_gpi_multi_xfer_timeout_handler(struct device *dev, struct geni_i2c_gpi_multi_desc_xfer *multi_xfer, - u32 transfer_timeout_msecs, + unsigned long timeout_jiffies, struct completion *transfer_comp) { int i; @@ -612,7 +629,7 @@ static int geni_i2c_gpi_multi_xfer_timeout_handler(struct device *dev, if (multi_xfer->msg_idx_cnt != multi_xfer->irq_cnt) { time_left = wait_for_completion_timeout(transfer_comp, - transfer_timeout_msecs); + timeout_jiffies); if (!time_left) { dev_err(dev, "%s: Transfer timeout\n", __func__); return -ETIMEDOUT; @@ -736,8 +753,16 @@ static int geni_i2c_gpi(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], dma_async_issue_pending(gi2c->tx_c); if ((msg_idx == (gi2c->num_msgs - 1)) || flags & DMA_PREP_INTERRUPT) { + unsigned long timeout; + size_t max_len = 0; + int j; + + for (j = 0; j < gi2c->num_msgs; j++) + max_len = max_t(size_t, max_len, msgs[j].len); + + timeout = geni_i2c_xfer_timeout(gi2c, max_len); ret = geni_i2c_gpi_multi_xfer_timeout_handler(gi2c->se.dev, gi2c_gpi_xfer, - XFER_TIMEOUT, &gi2c->done); + timeout, &gi2c->done); if (ret) { dev_err(gi2c->se.dev, "I2C multi write msg transfer timeout: %d\n", @@ -851,8 +876,10 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i } if (!gi2c->is_tx_multi_desc_xfer) { + unsigned long timeout = geni_i2c_xfer_timeout(gi2c, msgs[i].len); + dma_async_issue_pending(gi2c->tx_c); - time_left = wait_for_completion_timeout(&gi2c->done, XFER_TIMEOUT); + time_left = wait_for_completion_timeout(&gi2c->done, timeout); if (!time_left) { dev_err(gi2c->se.dev, "%s:I2C timeout\n", __func__); gi2c->err = -ETIMEDOUT; -- 2.34.1

1 week, 6 days

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