Messages in this thread | | | Date | Wed, 9 May 2018 11:35:05 +0100 | From | Brian Starkey <> | Subject | Re: [PATCH v9 11/15] vb2: add in-fence support to QBUF |
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Hi,
On Tue, May 08, 2018 at 08:18:06PM -0300, Gustavo Padovan wrote: > >Hi Hans, > >On Mon, 2018-05-07 at 14:07 +0200, Hans Verkuil wrote: >> On 04/05/18 22:06, Ezequiel Garcia wrote: >> > From: Gustavo Padovan <gustavo.padovan@collabora.com>
[snip]
>> > diff --git a/include/media/videobuf2-core.h >> > b/include/media/videobuf2-core.h >> > index 364e4cb41b10..28ce8f66882e 100644 >> > --- a/include/media/videobuf2-core.h >> > +++ b/include/media/videobuf2-core.h >> > @@ -17,6 +17,7 @@ >> > #include <linux/poll.h> >> > #include <linux/dma-buf.h> >> > #include <linux/bitops.h> >> > +#include <linux/dma-fence.h> >> > >> > #define VB2_MAX_FRAME (32) >> > #define VB2_MAX_PLANES (8) >> > @@ -255,12 +256,21 @@ struct vb2_buffer { >> > * done_entry: entry on the list that >> > stores all buffers ready >> > * to be dequeued to userspace >> > * vb2_plane: per-plane information; do not >> > change >> > + * in_fence: fence received from vb2 client >> > to wait on before >> > + * using the buffer (queueing to >> > the driver) >> > + * fence_cb: fence callback information >> > + * fence_cb_lock: protect callback signal/remove >> > */ >> > enum vb2_buffer_state state; >> > >> > struct vb2_plane planes[VB2_MAX_PLANES]; >> > struct list_head queued_entry; >> > struct list_head done_entry; >> > + >> > + struct dma_fence *in_fence; >> > + struct dma_fence_cb fence_cb; >> > + spinlock_t fence_cb_lock; >> > + >> >> So for the _MPLANE formats this is one fence for all planes. Which >> makes sense, but how >> does drm handle that? Also one fence for all planes? > >Yes, this is one fence for all planes. > >The DRM concept for planes is a totally different concept and is >basically a representation of an user definable square on the screen, >and to that plane there in one framebuffer attached - display hw has no >such a multiplanar for the same image AFAICT. So you probably need some >blit to convert the v4l2 multiplanar to a DRM framebuffer. >
Lots of display hardware can do multi-planar formats, and there's space in struct drm_framebuffer for up to 4 buffer handles (e.g. 3 handles are passed for Luma, Cr, and Cb when the framebuffer format is DRM_FORMAT_YUV420) - like V4L2 MPLANE.
The V4L2 code here matches with the DRM "explicit sync" (IN_FENCE_FD/OUT_FENCE_PTR) stuff, which is probably what we want. The main difference is that in DRM, explicit fences aren't associated with framebuffers, they're associated with the things using the framebuffers - but practically it doesn't make a difference.
There can be per-buffer "implicit sync" via dma-buf reservation objects, but I don't think this series should attempt to deal with that.
Cheers, -Brian
>> >> I think there should be a comment about this somewhere. > >Yes, we've been over this exact discussion a few times :) >Having entirely different things with the same name is quite confusing. > >Regards, > >Gustavo > >-- >Gustavo Padovan >Principal Software Engineer >Collabora Ltd.
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