On 2020-09-08 17:47, Christoph Hellwig wrote:
dma_declare_coherent_memory should not be in a DMA API guide aimed
at driver writers (that is consumers of the API). Move it to a comment
near the function instead.
I still think there might be an occasional valid use for device-local
memory outside the scope of platform code without the driver having to
go full ZONE_DEVICE/HMM/TTM, e.g. with stuff like PCIe-based FPGA
prototyping cards, but the kind of driver I'm imagining for that case
would never be upstream anyway (if it were even written, rather than
just using hard-coded hacks), so meh.
Reviewed-by: Robin Murphy
Signed-off-by: Christoph Hellwig
Documentation/core-api/dma-api.rst | 24
kernel/dma/coherent.c | 17 +
2 files changed, 17 insertions(+), 24 deletions(-)
diff --git a/Documentation/core-api/dma-api.rst
index 3b3a4b9a6f..90239348b30f6f 100644
@@ -586,30 +586,6 @@ the DMA_ATTR_NON_CONSISTENT flag starting at virtual
address vaddr and
continuing on for size. Again, you *must* observe the cache line
boundaries when doing this.
- dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
- dma_addr_t device_addr, size_t size);
-Declare region of memory to be handed out by dma_alloc_coherent() when
-it's asked for coherent memory for this device.
-phys_addr is the CPU physical address to which the memory is currently
-assigned (this will be ioremapped so the CPU can access the region).
-device_addr is the DMA address the device needs to be programmed
-with to actually address this memory (this will be handed out as the
-dma_addr_t in dma_alloc_coherent()).
-size is the size of the area (must be multiples of PAGE_SIZE).
-As a simplification for the platforms, only *one* such region of
-memory may be declared per device.
-For reasons of efficiency, most platforms choose to track the declared
-region only at the granularity of a page. For smaller allocations,
-you should use the dma_pool() API.
Part III - Debug drivers use of the DMA-API
diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c
index 2a0c4985f38e41..f85d14bbfcbe03 100644
@@ -107,6 +107,23 @@ static int dma_assign_coherent_memory(struct device *dev,
+ * Declare a region of memory to be handed out by dma_alloc_coherent() when it
+ * is asked for coherent memory for this device. This shall only be used
+ * from platform code, usually based on the device tree description.
+ * phys_addr is the CPU physical address to which the memory is currently
+ * assigned (this will be ioremapped so the CPU can access the region).
+ * device_addr is the DMA address the device needs to be programmed with to
+ * actually address this memory (this will be handed out as the dma_addr_t in
+ * dma_alloc_coherent()).
+ * size is the size of the area (must be a multiple of PAGE_SIZE).
+ * As a simplification for the platforms, only *one* such region of memory may
+ * be declared per device.
int dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
dma_addr_t device_addr, size_t size)
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