linux-kernel - Re: [PATCH] Allow S/G_PARM for stateful decoder

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Date:   Fri, 9 Sep 2022 14:16:48 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Dikshita Agarwal <quic_dikshita@...cinc.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     stanimir.varbanov@...aro.org, quic_vgarodia@...cinc.com,
        quic_majja@...cinc.com, quic_jdas@...cinc.com
Subject: Re: [PATCH] Allow S/G_PARM for stateful decoder

Hi Dikshita,

First I'll comment on this patch, then at the end I have more high-level
comments.

On 29/08/2022 09:54, Dikshita Agarwal wrote:
> Some stateful decoder supports S/G_PARM similar to a

decoder -> decoders

BTW, which decoder drivers support this in mainline? Or is this
for out-of-tree drivers?

> stateful encoder. S_PARM(OUTPUT) reserves hardware decoder
> resources, and G_PARM(CAPTURE) returns the embedded
> frame interval. Allow the same with this change.
> 
> Signed-off-by: Dikshita Agarwal <quic_dikshita@...cinc.com>
> ---
>  utils/v4l2-compliance/v4l2-test-formats.cpp | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/utils/v4l2-compliance/v4l2-test-formats.cpp b/utils/v4l2-compliance/v4l2-test-formats.cpp
> index 269a383..e996558 100644
> --- a/utils/v4l2-compliance/v4l2-test-formats.cpp
> +++ b/utils/v4l2-compliance/v4l2-test-formats.cpp
> @@ -64,8 +64,6 @@ static int testEnumFrameIntervals(struct node *node, __u32 pixfmt,
>  		ret = doioctl(node, VIDIOC_ENUM_FRAMEINTERVALS, &frmival);
>  		if (ret == ENOTTY)
>  			return ret;
> -		// M2M devices don't support this, except for stateful encoders
> -		fail_on_test(node->is_m2m && !(node->codec_mask & STATEFUL_ENCODER));

M2M devices still don't support this, except for stateful codecs. So this test
should still be there, just changed to:

!(node->codec_mask & (STATEFUL_ENCODER | STATEFUL_DECODER))

>  		if (f == 0 && ret == EINVAL) {
>  			if (type == V4L2_FRMSIZE_TYPE_DISCRETE)
>  				warn("found framesize %dx%d, but no frame intervals\n", w, h);
> @@ -1367,8 +1365,6 @@ static int testParmType(struct node *node, unsigned type)
>  	}
>  	if (ret == ENOTTY)
>  		return ret;
> -	// M2M devices don't support this, except for stateful encoders
> -	fail_on_test(node->is_m2m && !is_stateful_enc);

Similar.

>  	if (ret == EINVAL)
>  		return ENOTTY;
>  	if (ret)

But modifying the utility is something you only do if the spec has first been updated.
So the stateful decoder chapter needs to be modified so it explains how G/S_PARM
shall be used. And ideally have at least one driver that supports it.

Regards,

	Hans