linux-kernel - Re: [PATCH] media: venus: dec: Fix capture formats enumeration order

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Date:   Thu, 09 Mar 2023 16:18:53 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Jordan Crouse <jorcrous@...zon.com>,
        Enric Balletbo i Serra <eballetb@...hat.com>
Cc:     Dikshita Agarwal <quic_dikshita@...cinc.com>,
        linux-kernel@...r.kernel.org, Albert Esteve <aesteve@...hat.com>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Sergio Lopez <slp@...hat.com>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
        Vikash Garodia <quic_vgarodia@...cinc.com>,
        linux-arm-msm@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH] media: venus: dec: Fix capture formats enumeration order

Jordan Crouse <jorcrous@...zon.com> writes:

> On Tue, Mar 07, 2023 at 05:20:18PM +0100, Enric Balletbo i Serra wrote:

[...]

>> >
>> > But regardless, I think that it would be better for a driver to
>> > not change the order of advertised VIDIOC_ENUM_FMT pixel formats.
>> >
>> > Because what happens now is that a decoding that was previously
>> > working by default is not working anymore due a combination of
>> > the default being changed and S_FMT not working as expected.
>
> For my part, I was using the gstreamer v4l2 decoder which for some reason tries
> to verify it can support whatever format it gets with G_FMT *before*
> trying a S_FMT. I can't confirm or deny if S_FMT currently works or not.
>
> That said, I entirely agree with Javier. While it might be more
> bandwidth efficient, QC08C is a obscure format. It is far more likely that the
> average open source user would rather use a well known output format and, as
> has been mentioned, once S_FMT is fixed those in the know can use the other
> formats if they are working with other Qualcomm hardware blocks.
>

Agreed. The rule is that the kernel shouldn't regress user-space and the
patches that changed the default format certainly did that. So from that
point of view I think that this patch should land.

There's also Enric's point that NV12 is a more common format and supported
by more user-space programs. That's why think that regardless of the S_FMT
situation, makes sense to revert to the previous default behaviour.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat