Hi Matthias,
Am Dienstag, 3. Januar 2023, 18:12:24 CET schrieb Matthias Kaehlcke:
On Thu, Dec 22, 2022 at 11:26:26AM -0800, Doug Anderson wrote:
Hi,
On Wed, Dec 21, 2022 at 6:26 PM Matthias Kaehlcke mka@chromium.org
wrote:
The primary task of the onboard_usb_hub driver is to control the power of an onboard USB hub. The driver gets the regulator from the device tree property "vdd-supply" of the hub's DT node. Some boards have device tree nodes for USB hubs supported by this driver, but don't specify a "vdd-supply". This is not an error per se, it just means that the onboard hub driver can't be used for these hubs, so don't create platform devices for such nodes.
This change doesn't completely fix the reported regression. It should fix it for the RPi 3 B Plus and boards with similar hub configurations (compatible DT nodes without "vdd-supply"), boards that actually use the onboard hub driver could still be impacted by the race conditions discussed in that thread. Not creating the platform devices for nodes without "vdd-supply" is the right thing to do, independently from the race condition, which will be fixed in future patch.
Fixes: 8bc063641ceb ("usb: misc: Add onboard_usb_hub driver") Link: https://lore.kernel.org/r/d04bcc45-3471-4417-b30b-5cf9880d785d@i2se.com / Reported-by: Stefan Wahren stefan.wahren@i2se.com Signed-off-by: Matthias Kaehlcke mka@chromium.org
Changes in v2:
don't create platform devices when "vdd-supply" is missing,
rather than returning an error from _find_onboard_hub()
check for "vdd-supply" not "vdd" (Johan)
updated subject and commit message
added 'Link' tag (regzbot)
drivers/usb/misc/onboard_usb_hub_pdevs.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
I'm a tad bit skeptical.
It somehow feels a bit too much like "inside knowledge" to add this here. I guess the "onboard_usb_hub_pdevs.c" is already pretty entangled with "onboard_usb_hub.c", but I'd rather the "pdevs" file keep the absolute minimum amount of stuff in it and all of the details be in the other file.
If this was the only issue though, I'd be tempted to let it slide. As it is, I'm kinda worried that your patch will break Alexander Stein, who should have been CCed (I've CCed him now) or Icenowy Zheng (also CCed now). I believe those folks are using the USB hub driver primarily to drive a reset GPIO. Looking at the example in the bindings for one of them (genesys,gl850g.yaml), I even see that the reset-gpio is specified but not a vdd-supply. I think you'll break that?
Thanks for pointing that out. My assumption was that the regulator is needed for the driver to do anything useful, but you are right, the reset GPIO alone could be used in combination with an always-on regulator to 'switch the hub on and off'.
In general, it feels like it should actually be fine to create the USB hub driver even if vdd isn't supplied. Sure, it won't do a lot, but it shouldn't actively hurt anything. You'll just be turning off and on bogus regulators and burning a few CPU cycles. I guess the problem is some race condition that you talk about in the commit message. I'd rather see that fixed...
Yes, the race conditions needs to be fixed as well, I didn't have enough time to write and test a patch before taking a longer break for the holidays, so I only sent out this (supposed) partial mitigation.
That being said, if we want to be more efficient and not burn CPU cycles and memory in Stefan Wahren's case, maybe the USB hub driver itself could return a canonical error value from its probe when it detects that it has no useful job and then "onboard_usb_hub_pdevs" could just silently bail out?
_probe() could return an error, however onboard_hub_create_pdevs() can't rely on that, since the actual onboard_hub driver might not have been loaded yet when the function is called.
It would be nice not to instantiate the pdev and onboard_hub USB instances if the DT node has neither a 'vdd-supply' nor 'reset-gpios'. If we aren't ok with doing that in onboard_hub_create_pdevs() then at least the 'raw' platform device would be created. onboard_hub_probe() could still bail if both properties are absent, _find_onboard_hub() would have to check it again to avoid the deferred probing 'loop' for the USB instances.
I'm not really fond of checking for optional features like 'vdd-supply' and 'reset-gpios'. This issue will pop up again if some new optional feature is added again, e.g. power-domains.
Alternatively we could 'just' fix the race condition involving the 'attach work' and the onboard_hub driver is fully instantiated even on (certain) boards where it does nothing. It's relatively rare that USB hub nodes are specified in the DT (unless the intention is to use this driver) and CONFIG_USB_ONBOARD_HUB needs to be set for the instances to be created, so maybe creating the useless instances is not such a big deal.
IMHO creating a pdev shouldn't harm in any case. It's similar to having a DT node without a corresponding driver enabled or even existing. Also adding USB devices to DT is something which is to be expected. usb-device.yaml exists since 2020 and the txt version since 2016. Unfortunately I'm not able to reproduce this issue on a different platform where the same HUB but no reset-gpios is required. I also noticed that onboard-usb-hub raises the error
Failed to attach USB driver: -22
for each hub it is supposed to support.
Best regards, Alexander