Messages in this thread | | | Date | Tue, 31 Oct 2023 17:35:42 +0100 | From | Stefano Garzarella <> | Subject | Re: [PATCH v4] ALSA: virtio: use ack callback |
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On Fri, Oct 27, 2023 at 10:10:30AM -0400, Michael S. Tsirkin wrote: >On Fri, Oct 27, 2023 at 12:18:00PM +0200, Stefano Garzarella wrote: >> On Fri, Oct 27, 2023 at 11:27:40AM +0200, Takashi Iwai wrote: >> > On Wed, 25 Oct 2023 11:49:19 +0200, >> > Matias Ezequiel Vara Larsen wrote: >> > > >> > > This commit uses the ack() callback to determine when a buffer has been >> > > updated, then exposes it to guest. >> > > >> > > The current mechanism splits a dma buffer into descriptors that are >> > > exposed to the device. This dma buffer is shared with the user >> > > application. When the device consumes a buffer, the driver moves the >> > > request from the used ring to available ring. >> > > >> > > The driver exposes the buffer to the device without knowing if the >> > > content has been updated from the user. The section 2.8.21.1 of the >> > > virtio spec states that: "The device MAY access the descriptor chains >> > > the driver created and the memory they refer to immediately". If the >> > > device picks up buffers from the available ring just after it is >> > > notified, it happens that the content may be old. >> > > >> > > When the ack() callback is invoked, the driver exposes only the buffers >> > > that have already been updated, i.e., enqueued in the available ring. >> > > Thus, the device always picks up a buffer that is updated. >> > > >> > > For capturing, the driver starts by exposing all the available buffers >> > > to device. After device updates the content of a buffer, it enqueues it >> > > in the used ring. It is only after the ack() for capturing is issued >> > > that the driver re-enqueues the buffer in the available ring. >> > > >> > > Co-developed-by: Anton Yakovlev <anton.yakovlev@opensynergy.com> >> > > Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com> >> > > Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com> >> > >> > Applied now to for-next branch. >> >> Cool, thanks for that! >> >> I just wonder if we should CC stable since we are fixing a virtio >> specification violation. >> >> @Michael what do you think? >> >> Thanks, >> Stefano > > >Acked-by: Michael S. Tsirkin <mst@redhat.com> >Fixes: de3a9980d8c3 ("ALSA: virtio: add virtio sound driver") > > >The patch is too big for stable - more than 100 lines added. See: >Documentation/process/stable-kernel-rules.rst
Yeah, I see, thanks for sharing!
Stefano
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