Hi Arnd, ---- On Tue, 12 Jul 2022 18:08:10 +0800 Arnd Bergmann <arnd@xxxxxxxx> wrote --- > On Tue, Jul 12, 2022 at 11:58 AM Li Chen <me@linux.beauty> wrote: > > > On Tue, Jul 12, 2022 at 2:26 AM Li Chen <me@linux.beauty> wrote: > > > > ---- On Mon, 11 Jul 2022 21:28:10 +0800 Arnd Bergmann <arnd@xxxxxxxx> wrote --- > > > > > On Mon, Jul 11, 2022 at 2:24 PM Li Chen <me@linux.beauty> wrote: > > > > > The problem here is that the DT is meant to describe the platform in an OS > > > > > independent way, so having a binding that just corresponds to a user space > > > > > interface is not a good abstraction. > > > > > > > > Gotcha, but IMO dts + rmem is the only choice for our use case. In our real > > > > case, we use reg instead of size to specify the physical address, so > > > > memremap cannot be used. > > > > > > Does your hardware require a fixed address for the buffer? If it can be > > > anywhere in memory (or at least within a certain range) but just has to > > > be physically contiguous, the normal way would be to use a CMA area > > > to allocate from, which gives you 'struct page' backed pages. > > > > The limitation is our DSP can only access 32bit memory, but total dram is > 4G, so I cannot use > > "size = <...>" in our real case (it might get memory above 4G). I'm not sure if other vendors' DSP also has > > this limitation, if so, how do they deal with it if throughput matters. > > This is a common limitation that gets handled automatically by setting > the dma_mask of the device through the dma-ranges property in DT. > When the driver does dma_alloc_coherent() or similar to gets its buffer, > it will then allocate pages below this boundary. Thanks for the tip! I wasn't aware that dma-ranges can be used by devices other than PCIe controllers. > If you need a large contiguous memory area, then using CMA allows > you to specify a region of memory that is kept reserved for DMA > allocations, so a call to dma_alloc_coherent() on your device will > get contiguous pages from that area, and move other data in those > pages elsewhere if necessary. non-movable data is allocated from > pages outside of the CMA reserved area in this case. We need a large memory pool, around 2G. I will try CMA and dma-ranges later! Regards, Li
