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Date:   Fri, 03 Jul 2020 16:33:12 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     Jonas Karlman <jonas@...boo.se>, linux-media@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Hans Verkuil <hans.verkuil@...co.com>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Alexandre Courbot <acourbot@...omium.org>
Subject: Re: [PATCH 8/9] media: rkvdec: Add validate_fmt ops for pixelformat
 validation

On Fri, 2020-07-03 at 19:17 +0000, Jonas Karlman wrote:
> On 2020-07-03 16:58, Ezequiel Garcia wrote:
> > On Fri, 2020-07-03 at 06:55 +0000, Jonas Karlman wrote:
> > > On 2020-07-03 05:14, Ezequiel Garcia wrote:
> > > > Hi Jonas,
> > > > 
> > > > Thanks for working on this.
> > > > 
> > > > On Wed, 2020-07-01 at 21:56 +0000, Jonas Karlman wrote:
> > > > > Add an optional validate_fmt operation that is used to validate the
> > > > > pixelformat of CAPTURE buffers.
> > > > > 
> > > > > This is used in next patch to ensure correct pixelformat is used for 10-bit
> > > > > and 4:2:2 content.
> > > > > 
> > > > > Signed-off-by: Jonas Karlman <jonas@...boo.se>
> > > > > ---
> > > > >  drivers/staging/media/rkvdec/rkvdec.c | 8 ++++++++
> > > > >  drivers/staging/media/rkvdec/rkvdec.h | 1 +
> > > > >  2 files changed, 9 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/staging/media/rkvdec/rkvdec.c b/drivers/staging/media/rkvdec/rkvdec.c
> > > > > index b1de55aa6535..465444c58f13 100644
> > > > > --- a/drivers/staging/media/rkvdec/rkvdec.c
> > > > > +++ b/drivers/staging/media/rkvdec/rkvdec.c
> > > > > @@ -239,6 +239,14 @@ static int rkvdec_try_capture_fmt(struct file *file, void *priv,
> > > > >  	if (WARN_ON(!coded_desc))
> > > > >  		return -EINVAL;
> > > > >  
> > > > > +	if (coded_desc->ops->validate_fmt) {
> > > > > +		int ret;
> > > > > +
> > > > > +		ret = coded_desc->ops->validate_fmt(ctx, pix_mp->pixelformat);
> > > > > +		if (ret)
> > > > > +			return ret;
> > > > > +	}
> > > > > + 
> > > > 
> > > > I don't think this approach will be enough. Unless I'm mistaken,
> > > > it's perfectly legal as per the stateless spec to first
> > > > call S_FMT on the OUTPUT queue (which is propagated to the CAPTURE side),
> > > > and then set the SPS and other controls.
> > > 
> > > I agree that this will not be enough to cover all use cases stated in the spec.
> > > 
> > > > The application is not required to do a TRY_FMT after S_EXT_CTRLS.
> > > 
> > > If I remember correctly we were required to implement a TRY_FMT loop in
> > > ffmpeg due to cedrus defaulting to SUNXI_TILED_NV12 instead of linear NV12
> > > on platforms where display controller did not support the tiled modifier.
> > > 
> > > So having TRY_FMT as part of the init sequence has been my only test-case.
> > > 
> > > > What I believe is needed is for the S_EXT_CTRLS to modify
> > > > and restrict the CAPTURE format accordingly, so the application
> > > > gets the correct format on G_FMT (and restrict future TRY_FMT).
> > > 
> > > This sounds like a proper solution, I do belive we may have a chicken or
> > > the egg problem depending on if application call S_EXT_CTRLS or S_FMT first.
> > > 
> > 
> > IIUC, the order is specified in the stateless spec [1].
> > 
> > 1) S_FMT on OUTPUT (to set the coded pixelformat). CAPTURE format
> > format is propagated here and a default format is set.
> > 
> > 2) S_EXT_CTRLS, parameters are set. We don't do anything here,
> > but here we'd validate the SPS and restrict the CAPTURE pixelformat
> > (and perhaps reset the default CAPTURE pixelformat).
> > 
> > 3) G_FMT on CAPTURE.
> > 
> > 4) (optional) ENUM_FMT / S_FMT on CAPTURE, to negotiate
> > something different from default.
> 
> There is also the following scenario that we may need to support:
> 
> 1) S_FMT on OUTPUT, default CAPTURE format is set.
> 
> 2) skip S_EXT_CTRLS, mandatory controls is only validated in req_validate.
> 
> 3) G_FMT on CAPTURE, returns default CAPTURE format.
> 
> 4) S_FMT on CAPTURE, CAPTURE format is changed from default to selected format.
> 
> 5) STREAMON
> 
> From this point on I would expect S_EXT_CTRLS with a V4L2_CTRL_WHICH_REQUEST_VAL
> flag to reject any SPS not matching the selected CAPTURE format. Effectively
> allowing S_FMT to lock down a format instead of an initial S_EXT_CTRLS during init.
> 
> This means that we have to both allow and reject a SPS depending on the state.
> 

Isn't it cleaner from an API to require the SPS at (2), right before
G_FMT on CAPTURE?

Unless you think it has clear advantages to provide more flexibility
to the user, i.e. it will allow to support specific use-cases,
then I would avoid making this flexible.

The spec currently doesn mention step 2 as being optional, although
there is a note mentioning controls can be overwritten.

Thanks,
Ezequiel

> Regards,
> Jonas
> 
> > Regards,
> > Ezequiel 
> > 
> > [1] Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst
> > 
> > > I guess we may need to lock down on a format at whatever comes first,
> > > S_FMT on CAPTURE or S_EXT_CTRLS with SPS ctrl.
> > > 
> > > I have an idea on how this could be addressed, will explore and see
> > > if I can come up with something new.
> > > 
> > > Regards,
> > > Jonas
> > > 
> > > > Also, V4L2 spec asks drivers not to fail on S_FMT
> > > > format mismatch, but instead to adjust and return a legal format
> > > > back to the application [1].
> > > > 
> > > > Let me know what you think and thanks again.
> > > > 
> > > > Ezequiel
> > > > 
> > > > [1] Documentation/userspace-api/media/v4l/vidioc-g-fmt.rst
> > > > 
> > > > >  	for (i = 0; i < coded_desc->num_decoded_fmts; i++) {
> > > > >  		if (coded_desc->decoded_fmts[i] == pix_mp->pixelformat)
> > > > >  			break;
> > > > > diff --git a/drivers/staging/media/rkvdec/rkvdec.h b/drivers/staging/media/rkvdec/rkvdec.h
> > > > > index 2fc9f46b6910..be4fc3645cde 100644
> > > > > --- a/drivers/staging/media/rkvdec/rkvdec.h
> > > > > +++ b/drivers/staging/media/rkvdec/rkvdec.h
> > > > > @@ -64,6 +64,7 @@ vb2_to_rkvdec_decoded_buf(struct vb2_buffer *buf)
> > > > >  struct rkvdec_coded_fmt_ops {
> > > > >  	int (*adjust_fmt)(struct rkvdec_ctx *ctx,
> > > > >  			  struct v4l2_format *f);
> > > > > +	int (*validate_fmt)(struct rkvdec_ctx *ctx, u32 pixelformat);
> > > > >  	int (*start)(struct rkvdec_ctx *ctx);
> > > > >  	void (*stop)(struct rkvdec_ctx *ctx);
> > > > >  	int (*run)(struct rkvdec_ctx *ctx);


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