Hi Gerd,
> > If support for Blob resources is available, then dumb BOs created by
> > the driver can be considered as guest Blobs. And, for guest Blobs,
> > there is no need to do any transfers or flushes
>
> No. VIRTGPU_BLOB_FLAG_USE_SHAREABLE means the host (aka device in virtio
> terms) *can* create a shared mapping. So, the guest sends still needs to
> send transfer
> commands, and then the device can shortcut the transfer commands on the host
> side in
> case a shared mapping exists.
[Kasireddy, Vivek] Ok. IIUC, are you saying that the device may or may not
create a shared
mapping (meaning res->image) and that the driver should not make any
assumptions about
that and thus still do the transfers and flushes?
Also, could you please briefly explain what does
VIRTIO_GPU_BLOB_FLAG_USE_MAPPABLE
mean given that the spec does not describe these blob_flags clearly? This is
what the spec says:
"The driver MUST inform the device if the blob resource is used for
memory access, sharing between driver instances and/or sharing with
other devices. This is done via the \field{blob_flags} field."
And, what should be the default blob_flags value for a dumb bo if the userspace
does not
specify them?
>
> flush commands are still needed for dirty tracking.
>
> > but we do need to do set_scanout even if the FB has not changed as
> > part of plane updates.
>
> Sounds like you workaround host bugs. This should not be needed with properly
> implemented flush.
[Kasireddy, Vivek] With the patches I tested with:
https://lists.nongnu.org/archive/html/qemu-devel/2021-03/msg09786.html
I noticed that if we do not have res->image and only have res->blob, we have to
re-submit the blob/dmabuf and update the displaysurface if guest made updates
to it
(in this case same FB) which can only happen if we call set_scanout_blob. IIUC,
flush
only marks the area as dirty but does not re-submit the updated buffer/blob and
I see
a flicker if I let it do dpy_gfx_update().
Thanks,
Vivek
>
> take care,
> Gerd
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