On Tue, Mar 3, 2026 at 2:20 PM Maxime Ripard mripard@redhat.com wrote:
Hi,
On Tue, Mar 03, 2026 at 01:33:47PM +0100, Albert Esteve wrote:
Add a dma-buf heap for DT coherent reserved-memory (i.e., 'shared-dma-pool' without 'reusable' property), exposing one heap per region for userspace buffers.
The heap binds the heap device to each memory region so coherent allocations use the correct dev->dma_mem, and it defers registration until module_init when normal allocators are available.
Signed-off-by: Albert Esteve aesteve@redhat.com
drivers/dma-buf/dma-heap.c | 4 +- drivers/dma-buf/heaps/Kconfig | 9 + drivers/dma-buf/heaps/Makefile | 1 + drivers/dma-buf/heaps/coherent_heap.c | 426 ++++++++++++++++++++++++++++++++++ include/linux/dma-heap.h | 11 + include/linux/dma-map-ops.h | 7 + 6 files changed, 456 insertions(+), 2 deletions(-)
diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c index 88189d4e48561..ba87e5ac16ae2 100644 --- a/drivers/dma-buf/dma-heap.c +++ b/drivers/dma-buf/dma-heap.c @@ -390,8 +390,8 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
heap = dma_heap_create(exp_info); if (IS_ERR(heap)) {
pr_err("dma_heap: failed to create heap (%d)\n", PTR_ERR(heap));return PTR_ERR(heap);
pr_err("dma_heap: failed to create heap (%ld)\n", PTR_ERR(heap));return ERR_CAST(heap);This looks unrelated and should possibly be squashed into the previous patch that introduces dma_heap_create()?
+static int coherent_heap_init_dma_mask(struct device *dev) +{
int ret;ret = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(64));if (!ret)return 0;/* Fallback to 32-bit DMA mask */return dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(32));+}
Why do you need to mess with the DMA mask? I'd expect that device to be able to access everything.
When I tested I was getting: "reserved memory is beyond device's set DMA address range", so I tested if it was fixed with dma_coerce_mask_and_coherent() and/or dma_set_mask_coherent(). I did not debug the value of coherent_dma_mask, but given the error I assume it was not set properly? Ultimately, using the 64 bit mask fixed it, and I added a 32-bit fallback to ensure support for 32-bit systems.
+static int __coherent_heap_register(struct reserved_mem *rmem) +{
struct dma_heap_export_info exp_info;struct coherent_heap *coh_heap;struct device *heap_dev;int ret;if (!rmem || !rmem->name)return -EINVAL;coh_heap = kzalloc_obj(*coh_heap);if (!coh_heap)return -ENOMEM;coh_heap->rmem = rmem;coh_heap->name = kstrdup(rmem->name, GFP_KERNEL);if (!coh_heap->name) {ret = -ENOMEM;goto free_coherent_heap;}exp_info.name = coh_heap->name;exp_info.ops = &coherent_heap_ops;exp_info.priv = coh_heap;coh_heap->heap = dma_heap_create(&exp_info);if (IS_ERR(coh_heap->heap)) {ret = PTR_ERR(coh_heap->heap);goto free_name;}heap_dev = dma_heap_get_dev(coh_heap->heap);ret = coherent_heap_init_dma_mask(heap_dev);if (ret) {pr_err("coherent_heap: failed to set DMA mask (%d)\n", ret);goto destroy_heap;}ret = of_reserved_mem_device_init_with_mem(heap_dev, rmem);if (ret) {pr_err("coherent_heap: failed to initialize memory (%d)\n", ret);goto destroy_heap;}ret = dma_heap_register(coh_heap->heap);if (ret) {pr_err("coherent_heap: failed to register heap (%d)\n", ret);goto destroy_heap;}I guess it's more of a comment about your previous patch, but it's not clear to me why you needed to split dma_heap_add into dma_heap_create / _register. Can you expand a bit?
So first I tried to just use dma_heap_add() and then use the heap_dev afterward to call of_reserved_mem_device_init_with_mem(), but if that call failed, the error path required some kind dma_heap_remove() function as the heap was already registered by then.
In the CMA heap for example, dma_heap_add() is invoked at the end of the `init` function. Therefore, you do not have this issue, if it failed it means the heap was not added and you just need to clean everything else.
However, performing a remove() does not sound like something that can be done safely. I've spent some time thinking on alternatives, but splitting felt the best pattern.
This way I can: 1. Create the device 2. Call of_reserved_mem_device_init_with_mem 3. Register the heap
This places registration at the end, making every error path and cleanup easy to handle.
Also, the `dma_heap_add()` code already seemed to handle these two parts/phases implicitly with device_create(), so splitting felt architecturally sound.
diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h index 1b0ea43ba66c3..77e6cb66ffce1 100644 --- a/include/linux/dma-heap.h +++ b/include/linux/dma-heap.h @@ -9,10 +9,12 @@ #ifndef _DMA_HEAPS_H #define _DMA_HEAPS_H
+#include <linux/errno.h> #include <linux/types.h>
struct dma_heap; struct device; +struct reserved_mem;
/**
- struct dma_heap_ops - ops to operate on a given heap
@@ -53,4 +55,13 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info);
extern bool mem_accounting;
+#if IS_ENABLED(CONFIG_DMABUF_HEAPS_COHERENT) +int dma_heap_coherent_register(struct reserved_mem *rmem); +#else +static inline int dma_heap_coherent_register(struct reserved_mem *rmem) +{
return -EOPNOTSUPP;+} +#endif
#endif /* _DMA_HEAPS_H */
Do you still need that now that you switched to an iterator-like function?
diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h index 60b63756df821..c87e5e44e5383 100644 --- a/include/linux/dma-map-ops.h +++ b/include/linux/dma-map-ops.h @@ -12,6 +12,7 @@
struct cma; struct iommu_ops; +struct reserved_mem;
struct dma_map_ops { void *(*alloc)(struct device *dev, size_t size, @@ -161,6 +162,7 @@ int dma_alloc_from_dev_coherent(struct device *dev, ssize_t size, int dma_release_from_dev_coherent(struct device *dev, int order, void *vaddr); int dma_mmap_from_dev_coherent(struct device *dev, struct vm_area_struct *vma, void *cpu_addr, size_t size, int *ret); +struct reserved_mem *dma_coherent_get_reserved_region(unsigned int idx); #else static inline int dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr, dma_addr_t device_addr, size_t size) @@ -172,6 +174,11 @@ static inline int dma_declare_coherent_memory(struct device *dev, #define dma_release_from_dev_coherent(dev, order, vaddr) (0) #define dma_mmap_from_dev_coherent(dev, vma, vaddr, order, ret) (0) static inline void dma_release_coherent_memory(struct device *dev) { } +static inline +struct reserved_mem *dma_coherent_get_reserved_region(unsigned int idx) +{
return NULL;+} #endif /* CONFIG_DMA_DECLARE_COHERENT */
#ifdef CONFIG_DMA_GLOBAL_POOL
To preserve bisectability, you shouldn't do it that way. Introduce this function into a preliminary patch, and then use it in this one.
Maxime