[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC] virtio_ring: check dma_mem for xen_domain
On Fri, 25 Jan 2019, Peng Fan wrote: > > On Wed, Jan 23, 2019 at 01:04:33PM -0800, Stefano Stabellini wrote: > > > If vring_use_dma_api is actually supposed to return true when > > > dma_dev->dma_mem is set, then both Peng's patch and the patch I wrote > > > are not fixing the real issue here. > > > > > > I don't know enough about remoteproc to know where the problem > > > actually lies though. > > > > The problem is the following: > > > > Devices can declare a specific memory region that they want to use when the > > driver calls dma_alloc_coherent for the device, this is done using the > > shared-dma-pool DT attribute, which comes in two variants that would be a > > little to much to explain here. > > > > remoteproc makes use of that because apparently the device can only > > communicate using that region. But it then feeds back memory obtained > > with dma_alloc_coherent into the virtio code. For that it calls > > vmalloc_to_page on the dma_alloc_coherent, which is a huge no-go for the > > ĐMA API and only worked accidentally on a few platform, and apparently > > arm64 just changed a few internals that made it stop working for remoteproc. > > > > The right answer is to not use the DMA API to allocate memory from a > > device-speficic region, but to tie the driver directly into the DT reserved > > memory API in a way that allows it to easilt obtain a struct device for it. > > Just have a question, > > Since vmalloc_to_page is ok for cma area, no need to take cma and per device > cma into consideration right? > > we only need to implement a piece code to handle per device specific region > using RESERVEDMEM_OF_DECLARE, just like: > RESERVEDMEM_OF_DECLARE(rpmsg-dma, "rpmsg-dma-pool", > rmem_rpmsg_dma_setup); > And implement the device_init call back and build a map between page and phys. > Then in rpmsg driver, scatter list could use page structure, no need > vmalloc_to_page > for per device dma. > > Is this the right way? I CC'ed the rpmsg maintainers, you want to keep them in the loop on this. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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