From: Steve Longerbeam <slongerbeam@gmail.com>
Subject: Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit
 controls from a pipeline
To: Russell King - ARM Linux <linux@armlinux.org.uk>
References: <20170303230645.GR21222@n2100.armlinux.org.uk>
 <20170304131329.GV3220@valkosipuli.retiisi.org.uk>
 <a7b8e095-a95c-24bd-b1e9-e983f18061c4@xs4all.nl>
 <20170310120902.1daebc7b@vento.lan>
 <5e1183f4-774f-413a-628a-96e0df321faf@xs4all.nl>
 <20170311101408.272a9187@vento.lan>
 <20170311153229.yrdjmggb3p2suhdw@ihha.localdomain>
 <acfb5eca-ff00-6d57-339a-3322034cbdb3@gmail.com>
 <20170311184551.GD21222@n2100.armlinux.org.uk>
 <1f1b350a-5523-34bc-07b7-f3cd2d1fd4c1@gmail.com>
 <20170311185959.GF21222@n2100.armlinux.org.uk>
Cc: mark.rutland@arm.com, andrew-ct.chen@mediatek.com,
        minghsiu.tsai@mediatek.com, nick@shmanahar.org,
        songjun.wu@microchip.com, Hans Verkuil <hverkuil@xs4all.nl>,
        pavel@ucw.cz, shuah@kernel.org, devel@driverdev.osuosl.org,
        markus.heiser@darmarIT.de, laurent.pinchart+renesas@ideasonboard.com,
        robert.jarzmik@free.fr,
        Mauro Carvalho Chehab <mchehab@s-opensource.com>, geert@linux-m68k.org,
        p.zabel@pengutronix.de, linux-media@vger.kernel.org,
        devicetree@vger.kernel.org, kernel@pengutronix.de, arnd@arndb.de,
        tiffany.lin@mediatek.com, bparrot@ti.com, robh+dt@kernel.org,
        horms+renesas@verge.net.au, mchehab@kernel.org,
        linux-arm-kernel@lists.infradead.org,
        niklas.soderlund+renesas@ragnatech.se, gregkh@linuxfoundation.org,
        linux-kernel@vger.kernel.org, Sakari Ailus <sakari.ailus@iki.fi>,
        jean-christophe.trotin@st.com, sakari.ailus@linux.intel.com,
        fabio.estevam@nxp.com, shawnguo@kernel.org, sudipm.mukherjee@gmail.com
Message-ID: <4917d7fb-2f48-17cd-aa2f-d54b0f19ed6e@gmail.com>
Date: Sat, 11 Mar 2017 19:31:18 -0800
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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