linux-kernel - Re: [PATCH 0/3] media: vimc: Add support for GBR and BGR formats on source pad of debayer

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Date:   Sun, 09 Feb 2020 18:26:10 +0000
From:   Nícolas F. R. A. Prado 
        <nfraprado@...tonmail.com>
To:     Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:     linux-media <linux-media@...r.kernel.org>,
        Helen Koike <helen.koike@...labora.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        lkcamp@...ts.libreplanetbr.org
Subject: Re: [PATCH 0/3] media: vimc: Add support for GBR and BGR formats on source pad of debayer

Hi,
Ezequiel.

On Sun, Feb 09, 2020 at 02:09:17PM -0300, Ezequiel Garcia wrote:
> 
> On Sun, 2 Feb 2020 at 12:50, Nícolas F. R. A. Prado
> <nfraprado@...tonmail.com> wrote:
> >
> > The objective of this series is to add support for GBR and BGR media bus formats
> > for the source pad of debayer subdevices of the vimc driver.
> >
> 
> Can you elaborate why is this needed, e.g. what use-case is this enabling,
> or what is this fixing?

Sure.

At the moment, the only supported media bus format on the source pad of
the debayer subdevice is the RGB888_1X24.

The mbus format of the source pad of the debayer ultimately determines the
pixelformat that is streamed on /dev/video3, since:
    * The mbus formats of the links on the topology have to match for the
        streaming to be possible, and [1] shows that the source pad of the
        debayer links to the sink of the scaler.
    * The scaler uses the same mbus format on sink and source.
    * The source pad of the scaler is linked to the /dev/video3 Capture.

That said, there isn't a GBR pixelformat, so it uses the RGB pixelformat.

So what this patch series enables:
    * Setting debayer and scaler subdevices to use GBR and BGR mbus formats.
    * Stream video using the BGR pixelformat from /dev/video3.

By enabling these, it makes it possible to use vimc to emulate hardware that
uses GBR or BGR mbus formats internally or that streams using the BGR
pixelformat.

Regards,
Nícolas

[1] https://linuxtv.org/downloads/v4l-dvb-apis-new/v4l-drivers/vimc.html#topology

> 
> Thanks,
> Ezequiel