linux-kernel - Re: [PATCH v5 05/10] media: v4l: Add definition for the Aspeed JPEG format

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Date:   Tue, 23 Nov 2021 12:23:56 +0200
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Jammy Huang <jammy_huang@...eedtech.com>
Cc:     "eajames@...ux.ibm.com" <eajames@...ux.ibm.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "hverkuil-cisco@...all.nl" <hverkuil-cisco@...all.nl>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 05/10] media: v4l: Add definition for the Aspeed JPEG
 format

Hi Jammy,

On Fri, Nov 19, 2021 at 10:02:40AM +0800, Jammy Huang wrote:
> Hi Sakari,
> 
> On 2021/11/18 下午 08:33, Sakari Ailus wrote:
> > Hi Jammy,
> > 
> > On Thu, Nov 18, 2021 at 03:40:26PM +0800, Jammy Huang wrote:
> > > This introduces support for the Aspeed JPEG format, where the new frame
> > > can refer to previous frame to reduce the amount of compressed data. The
> > > concept is similar to I/P frame of video compression. I will compare the
> > > new frame with previous one to decide which macroblock's data is
> > > changed, and only the changed macroblocks will be compressed.
> > > 
> > > This Aspeed JPEG format is used by the video engine on Aspeed platforms,
> > > which is generally adapted for remote KVM.
> > > 
> > > Signed-off-by: Jammy Huang <jammy_huang@...eedtech.com>
> > > ---
> > > v5:
> > >    - no update
> > > v4:
> > >    - new
> > > ---
> > >   Documentation/media/uapi/v4l/pixfmt-reserved.rst | 12 ++++++++++++
> > >   drivers/media/v4l2-core/v4l2-ioctl.c             |  1 +
> > >   include/uapi/linux/videodev2.h                   |  1 +
> > >   3 files changed, 14 insertions(+)
> > > 
> > > diff --git a/Documentation/media/uapi/v4l/pixfmt-reserved.rst b/Documentation/media/uapi/v4l/pixfmt-reserved.rst
> > > index b2cd155e691b..23c05063133d 100644
> > > --- a/Documentation/media/uapi/v4l/pixfmt-reserved.rst
> > > +++ b/Documentation/media/uapi/v4l/pixfmt-reserved.rst
> > > @@ -264,6 +264,18 @@ please make a proposal on the linux-media mailing list.
> > >   	of tiles, resulting in 32-aligned resolutions for the luminance plane
> > >   	and 16-aligned resolutions for the chrominance plane (with 2x2
> > >   	subsampling).
> > > +    * .. _V4L2-PIX-FMT-AJPG:
> > > +
> > > +      - ``V4L2_PIX_FMT_AJPG``
> > > +      - 'AJPG'
> > > +      - ASPEED JPEG format used by the aspeed-video driver on Aspeed platforms,
> > > +        which is generally adapted for remote KVM.
> > > +        On each frame compression, I will compare the new frame with previous
> > > +        one to decide which macroblock's data is changed, and only the changed
> > > +        macroblocks will be compressed.
> > > +
> > > +        You could reference to chapter 36, Video Engine, of AST2600's datasheet
> > > +        for more information.
> > Is this datasheet publicly available? Do you have a URL?
> 
> Sorry, this datasheet is not publicly available.
> Hans mentioned this as well in the discussion below:
> 
> https://lkml.org/lkml/2021/11/10/101

If the vendor documentation is not publicly available, you'll need to have
the format documented here. Alternatively an open source implementation
(e.g. LGPL) is presumably fine, too.

-- 
Regards,

Sakari Ailus