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Subject: Re: [PATCH v3 1/3] media: rkvdec: Fix .buf_prepare
From:   Ezequiel Garcia <ezequiel@collabora.com>
To:     Tomasz Figa <tfiga@chromium.org>
Cc:     Linux Media Mailing List <linux-media@vger.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        kernel@collabora.com, Jonas Karlman <jonas@kwiboo.se>,
        Heiko Stuebner <heiko@sntech.de>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Alexandre Courbot <acourbot@chromium.org>,
        Jeffrey Kardatzke <jkardatzke@chromium.org>,
        Gustavo Padovan <gustavo.padovan@collabora.com>
Date:   Tue, 05 May 2020 11:27:30 -0300
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On Tue, 2020-05-05 at 16:05 +0200, Tomasz Figa wrote:
> On Tue, May 5, 2020 at 3:59 PM Ezequiel Garcia <ezequiel@collabora.com> wrote:
> > On Tue, 2020-05-05 at 15:56 +0200, Tomasz Figa wrote:
> > > Hi Ezequiel,
> > > 
> > > On Tue, May 5, 2020 at 3:41 PM Ezequiel Garcia <ezequiel@collabora.com> wrote:
> > > > The driver should only set the payload on .buf_prepare
> > > > if the buffer is CAPTURE type, or if an OUTPUT buffer
> > > > has a zeroed payload.
> > > 
> > > Thanks for the patch. Just one question below.
> > > 
> > > Where does the requirement to set OUTPUT buffer bytesused to sizeimage
> > > if the original bytesused is 0 come from?
> > > 
> > 
> > If I'm reading english correctly, it's here:
> > 
> > https://www.kernel.org/doc/html/latest/media/uapi/v4l/buffer.html
> > 
> > """
> > The number of bytes occupied by the data in the buffer. It depends on the negotiated data format and may change with each buffer for compressed
> > variable size data like JPEG images. Drivers must set this field when type refers to a capture stream, applications when it refers to an output
> > stream. If the application sets this to 0 for an output stream, then bytesused will be set to the size of the buffer (see the length field of this
> > struct) by the driver. For multiplanar formats this field is ignored and the planes pointer is used instead.
> > """
> 
> Okay, thanks. I wonder if this shouldn't be handled by the core,
> though. Especially given that the document refers to the length field
> specifically and not the sizeimage set in the format.
> 

Yes, either core or helper, this definitely calls for a generic solution.

Ezequiel