Linux Virtualization - Dec 2016 - [RFC LINUX PATCH 0/2] Virtio ring works with DMA coherent memory

RPMsg uses dma_alloc_coherent() to allocate memory to shared with the remote.
In this case, as there is no pages setup in the dma_alloc_coherent(),
we cannot get the physical address back from the virtual address, and thus,
we can set the sg_dma_addr to store the DMA address and mark it already DMA
mapped.

When virtio vring sees the sg_dma_addr is ready set, do not call dma_map_page().

The issue was once discussed here:
http://virtualization.linux-foundation.narkive.com/CfVP32Vy/rfc-0-4-rpmsg-fix-init-of-dma-able-virtqueues

Edgar E. Iglesias (1):
  rpmsg: DMA map sgs passed to virtio

Wendy Liang (1):
  virtio_ring: Do not call dma_map_page if sg is already mapped.

 drivers/rpmsg/virtio_rpmsg_bus.c | 22 +++++++++++++++++++---
 drivers/virtio/virtio_ring.c     |  6 ++++++
 2 files changed, 25 insertions(+), 3 deletions(-)

-- 
1.9.1

On 2016?12?07? 02:21, Wendy Liang wrote:
> RPMsg uses dma_alloc_coherent() to allocate memory to shared with the
remote.
> In this case, as there is no pages setup in the dma_alloc_coherent(),
> we cannot get the physical address back from the virtual address, and thus,
> we can set the sg_dma_addr to store the DMA address and mark it already DMA
> mapped.
>
> When virtio vring sees the sg_dma_addr is ready set, do not call
dma_map_page().
>
> The issue was once discussed here:
>
http://virtualization.linux-foundation.narkive.com/CfVP32Vy/rfc-0-4-rpmsg-fix-init-of-dma-able-virtqueues
>
> Edgar E. Iglesias (1):
>    rpmsg: DMA map sgs passed to virtio
>
> Wendy Liang (1):
>    virtio_ring: Do not call dma_map_page if sg is already mapped.
>
>   drivers/rpmsg/virtio_rpmsg_bus.c | 22 +++++++++++++++++++---
>   drivers/virtio/virtio_ring.c     |  6 ++++++
>   2 files changed, 25 insertions(+), 3 deletions(-)
>
Looks good to me.

I think you can send a formal patch (without RFC prefix).

Thanks

Thanks Jason, I will resend it as a formal patch.

Wendy
> -----Original Message-----
> From: Jason Wang [mailto:jasowang at redhat.com]
> Sent: Wednesday, December 07, 2016 7:18 PM
> To: Jiaying Liang; ohad at wizery.com; bjorn.andersson at linaro.org;
linux-
> remoteproc at vger.kernel.org; mst at redhat.com; virtualization at
lists.linux-
> foundation.org
> Cc: Jiaying Liang
> Subject: Re: [RFC LINUX PATCH 0/2] Virtio ring works with DMA coherent
> memory
>
>
>
> On 2016?12?07? 02:21, Wendy Liang wrote:
> > RPMsg uses dma_alloc_coherent() to allocate memory to shared with the
> remote.
> > In this case, as there is no pages setup in the dma_alloc_coherent(),
> > we cannot get the physical address back from the virtual address, and
> > thus, we can set the sg_dma_addr to store the DMA address and mark it
> > already DMA mapped.
> >
> > When virtio vring sees the sg_dma_addr is ready set, do not call
> dma_map_page().
> >
> > The issue was once discussed here:
> > http://virtualization.linux-foundation.narkive.com/CfVP32Vy/rfc-0-4-rp
> > msg-fix-init-of-dma-able-virtqueues
> >
> > Edgar E. Iglesias (1):
> >    rpmsg: DMA map sgs passed to virtio
> >
> > Wendy Liang (1):
> >    virtio_ring: Do not call dma_map_page if sg is already mapped.
> >
> >   drivers/rpmsg/virtio_rpmsg_bus.c | 22 +++++++++++++++++++---
> >   drivers/virtio/virtio_ring.c     |  6 ++++++
> >   2 files changed, 25 insertions(+), 3 deletions(-)
> >
>
> Looks good to me.
>
> I think you can send a formal patch (without RFC prefix).
>
> Thanks

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