Re: [PATCH virtio] virtio: virtio_console: fix DMA memory allocation for rproc serial

[Michael S. Tsirkin]

On Tue, Nov 17, 2020 at 02:02:30PM +0000, Christoph Hellwig wrote:
> On Tue, Nov 17, 2020 at 03:00:32PM +0100, Arnaud POULIQUEN wrote:
> > The dma_declare_coherent_memory allows to associate vdev0buffer memory region
> > to the remoteproc virtio device (vdev parent). This region is used to allocated
> > the rpmsg buffers.
> > The memory for the rpmsg buffer is allocated by the rpmsg_virtio device in
> > rpmsg_virtio_bus[1]. The size depends on the total size needed for the rpmsg
> > buffers.
> > 
> > The vrings are allocated directly by the remoteproc device.
> 
> Weird.  I thought virtio was pretty strict in not allowing diret DMA
> API usage in drivers to support the legacy no-mapping case.

Well remoteproc is weird in that it's use of DMA API precedes
standartization efforts, and it was never standardized in the virtio
spec ..

> Either way, the point stands:  if you want these magic buffers handed
> out to specific rpmsg instances I think not having to detour through the
> DMA API is going to make everyones life easier.