linux-kernel - Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline

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Date:   Sat, 11 Mar 2017 19:31:18 -0800
From:   Steve Longerbeam <slongerbeam@...il.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     mark.rutland@....com, andrew-ct.chen@...iatek.com,
        minghsiu.tsai@...iatek.com, nick@...anahar.org,
        songjun.wu@...rochip.com, Hans Verkuil <hverkuil@...all.nl>,
        pavel@....cz, shuah@...nel.org, devel@...verdev.osuosl.org,
        markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, robert.jarzmik@...e.fr,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        geert@...ux-m68k.org, p.zabel@...gutronix.de,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        kernel@...gutronix.de, arnd@...db.de, tiffany.lin@...iatek.com,
        bparrot@...com, robh+dt@...nel.org, horms+renesas@...ge.net.au,
        mchehab@...nel.org, linux-arm-kernel@...ts.infradead.org,
        niklas.soderlund+renesas@...natech.se, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, Sakari Ailus <sakari.ailus@....fi>,
        jean-christophe.trotin@...com, sakari.ailus@...ux.intel.com,
        fabio.estevam@....com, shawnguo@...nel.org,
        sudipm.mukherjee@...il.com
Subject: Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit
 controls from a pipeline



On 03/11/2017 10:59 AM, Russell King - ARM Linux wrote:
> On Sat, Mar 11, 2017 at 10:54:55AM -0800, Steve Longerbeam wrote:
>>
>>
>> On 03/11/2017 10:45 AM, Russell King - ARM Linux wrote:
>>> I really don't think expecting the user to understand and configure
>>> the pipeline is a sane way forward.  Think about it - should the
>>> user need to know that, because they have a bayer-only CSI data
>>> source, that there is only one path possible, and if they try to
>>> configure a different path, then things will just error out?
>>>
>>> For the case of imx219 connected to iMX6, it really is as simple as
>>> "there is only one possible path" and all the complexity of the media
>>> interfaces/subdevs is completely unnecessary.  Every other block in
>>> the graph is just noise.
>>>
>>> The fact is that these dot graphs show a complex picture, but reality
>>> is somewhat different - there's only relatively few paths available
>>> depending on the connected source and the rest of the paths are
>>> completely useless.
>>>
>>
>> I totally disagree there. Raw bayer requires passthrough yes, but for
>> all other media bus formats on a mipi csi-2 bus, and all other media
>> bus formats on 8-bit parallel buses, the conersion pipelines can be
>> used for scaling, CSC, rotation, and motion-compensated de-interlacing.
>
> ... which only makes sense _if_ your source can produce those formats.
> We don't actually disagree on that.

...and there are lots of those sources! You should try getting out of
your imx219 shell some time, and have a look around! :)

>
> Let me re-state.  If the source can _only_ produce bayer, then there is
> _only_ _one_ possible path, and all the overhead of the media controller
> stuff is totally unnecessary.
>
> Or, are you going to tell me that the user should have the right to
> configure paths through the iMX6 hardware that are not permitted by the
> iMX6 manuals for the data format being produced by the sensor?

Anyway, no the user is not allowed to configure a path that is not
allowed by the hardware, such as attempting to pass raw bayer through
an Image Converter path.

I guess you are simply commenting that for users of bayer sensors, the
other pipelines can be "confusing". But I trust you're not saying those
other pipelines should therefore not be present, which would be a
completely nutty argument.

Steve