From: Andy Duan Sent: 2018年12月28日 9:48 > From: Christoph Hellwig <hch@xxxxxxxxxxxxx> Sent: 2018年12月27日 > 20:19 > > On Thu, Dec 27, 2018 at 02:36:53AM +0000, Andy Duan wrote: > > > Rpmsg is used to communicate with remote cpu like M4, the allocated > > > memory is shared by Linux and M4 side. In general, Linux side > > > reserved the static memory region like per-device DMA pool as > > > coherent memory for the RPMSG receive/transmit buffers. For the > > > static memory region, normal page allocator cannot match the > > > requirement unless there have protocol to tell M4 the dynamic RPMSG > receive/transmit buffers. > > > > In that case you need a OF reserved memory node, like we use for the > > "shared-dma-pool" coherent or contiguous allocations. Currently we > > have those two variants wired up the the DMA allocator, but they can > > also used directly by drivers. To be honest I don't really like like > > drivers getting too intimate with the memory allocator, but I also > > don't think that providing a little glue code to instanciat a CMA pool > > for a memory that can be used directly by the driver is much of an > > issue. Most of it could be reused from the existing code, just with a slightly > lower level interfaces. > > > > > To stop to extract pages from dma_alloc_coherent, the rpmsg bus > > > implementation base on virtio that already use the scatterlist > > > mechanism for vring memory. So for virtio driver like RPMSG bus, we > > > have to extract pages from dma_alloc_coherent. > > > > This sentence doesn't parse for me. > > Virtio supply the APIs that require the scatterlist pages for virtio in/out buf: > int virtqueue_add_inbuf(struct virtqueue *vq, > struct scatterlist *sg, unsigned int num, > void *data, > gfp_t gfp) > int virtqueue_add_outbuf(struct virtqueue *vq, > struct scatterlist *sg, unsigned int num, > void *data, > gfp_t gfp) > > > > > > > I don't think the patch is one hack, as we already know the > > > physical address for the coherent memory, just want to get pages, > > > the interface "pfn_to_page(PHYS_PFN(x))" is very reasonable to the > > > related pages. > > > > struct scatterlist doesn't (directly) refer to physical address, it > > refers to page structures, which encode a kernel virtual address in > > the kernel direct mapping, and we intentionally do not guarantee a > > return in the kernel direct mapping for the DMA coherent allocator, as > > in many cases we have to either allocate from a special pool, from a > > special address window or remap memory to mark it as uncached. How > > that is done is an implenentation detail that is not exposed to drivers and > may change at any time. > > > > > If you stick to use normal page allocator and streaming DMA API in > > > RPMSG, then we have to: > > > - add new quirk feature for virtio like the same function as > > > "VIRTIO_F_IOMMU_PLATFORM", > > > > You have to do that anyway. > > I discuss with our team, use page allocator cannot match our requirement. > i.MX8QM/QXP platforms have partition feature that limit M4 only access fixed > ddr memory region. Suppose other platforms also have similar limitation for > secure case. > > So it requires to use OF reserved memory for the "shared-dma-pool" coherent > or contiguous allocations. > Do you have any other comments for the patch ? Current driver break remoteproc on NXP i.MX8 platform , the patch is bugfix the virtio rpmsg bus, we hope the patch enter to next and stable tree if no other comments.
