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 <robin.murphy@xxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx> --- 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 b/Documentation/core-api/dma-api.rst index 3b3abbbb4b9a6f..90239348b30f6f 100644 --- a/Documentation/core-api/dma-api.rst +++ b/Documentation/core-api/dma-api.rst @@ -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.-::- - int - 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 --- a/kernel/dma/coherent.c +++ b/kernel/dma/coherent.c @@ -107,6 +107,23 @@ static int dma_assign_coherent_memory(struct device *dev, return 0; }+/*+ * 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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