Re: [PATCH for 5.4] media: hantro: Fix s_fmt for dynamic resolution changes

[Philipp Zabel <p.zabel@pengutronix.de>]

On Wed, 2019-09-04 at 10:01 -0300, Ezequiel Garcia wrote:
> On Wed, 2019-09-04 at 12:13 +0200, Philipp Zabel wrote:
> > Hi Ezequiel,
> > 
> > On Tue, 2019-09-03 at 14:12 -0300, Ezequiel Garcia wrote:
> > > Commit 953aaa1492c53 ("media: rockchip/vpu: Prepare things to support decoders")
> > > changed the conditions under S_FMT was allowed for OUTPUT
> > > CAPTURE buffers.
> > > 
> > > However, and according to the mem-to-mem stateless decoder specification,
> > > in order to support dynamic resolution changes, S_FMT should be allowed
> > > even if OUTPUT buffers have been allocated.
> > > 
> > > Relax decoder S_FMT restrictions on OUTPUT buffers, allowing a resolution
> > > modification, provided the pixel format stays the same.
> > > 
> > > Tested on RK3288 platforms using ChromiumOS Video Decode/Encode Accelerator Unittests.
> > > 
> > > Fixes: 953aaa1492c53 ("media: rockchip/vpu: Prepare things to support decoders")
> > > Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
> > > ---
> > >  drivers/staging/media/hantro/hantro_v4l2.c | 22 ++++++++++++++++------
> > >  1 file changed, 16 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/staging/media/hantro/hantro_v4l2.c b/drivers/staging/media/hantro/hantro_v4l2.c
> > > index 3dae52abb96c..d48b548842cf 100644
> > > --- a/drivers/staging/media/hantro/hantro_v4l2.c
> > > +++ b/drivers/staging/media/hantro/hantro_v4l2.c
> > > @@ -367,19 +367,22 @@ vidioc_s_fmt_out_mplane(struct file *file, void *priv, struct v4l2_format *f)
> > >  {
> > >  	struct v4l2_pix_format_mplane *pix_mp = &f->fmt.pix_mp;
> > >  	struct hantro_ctx *ctx = fh_to_ctx(priv);
> > > +	struct vb2_queue *vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx, f->type);
> > >  	const struct hantro_fmt *formats;
> > >  	unsigned int num_fmts;
> > > -	struct vb2_queue *vq;
> > >  	int ret;
> > >  
> > > -	/* Change not allowed if queue is busy. */
> > > -	vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx, f->type);
> > > -	if (vb2_is_busy(vq))
> > > -		return -EBUSY;
> > > -
> > >  	if (!hantro_is_encoder_ctx(ctx)) {
> > >  		struct vb2_queue *peer_vq;
> > >  
> > > +		/*
> > > +		 * In other to support dynamic resolution change,
> > > +		 * the decoder admits a resolution change, as long
> > > +		 * as the pixelformat remains. Can't be done if streaming.
> > > +		 */
> > > +		if (vb2_is_streaming(vq) || (vb2_is_busy(vq) &&
> > > +		    pix_mp->pixelformat != ctx->src_fmt.pixelformat))
> > 
> > Before using contents of the v4l2_format f for comparison, we should run
> > vidioc_try_fmt_out_mplane over it.
> 
> Right, good catch.
> 
> >  Also, besides pixelformat, sizeimage
> > shouldn't change either, at least if this is a VB2_MMAP queue.
> > 
> 
> This is the OUTPUT queue, so I don't see why the sizeimage
> of the coded buffers should stay the same. Maybe I'm missing
> something? 

If the OUTPUT vb2_queue is busy, we already have some buffers of the old
size allocated. We can't change their size dynamically with just
VIDIOC_S_FMT.

Maybe this should correct sizeimage to the old size instead of returning
-EBUSY? Either way, if the old buffer size is too small to reasonably
decode the new resolution, the OUTPUT buffers have to be reallocated.

regards
Philipp