Subject: Re: [PATCH v5 38/39] media: imx: csi: fix crop rectangle reset in
 sink set_fmt
To: Philipp Zabel <p.zabel@pengutronix.de>,
        Russell King - ARM Linux <linux@armlinux.org.uk>
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 <1490018451.2917.86.camel@pengutronix.de>
Cc: robh+dt@kernel.org, mark.rutland@arm.com, shawnguo@kernel.org,
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        sakari.ailus@linux.intel.com, pavel@ucw.cz, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-media@vger.kernel.org, devel@driverdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@mentor.com>
From: Steve Longerbeam <slongerbeam@gmail.com>
Message-ID: <709728d3-83ab-90cf-44d4-dcf41e6fbee7@gmail.com>
Date: Mon, 20 Mar 2017 12:48:11 -0700
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On 03/20/2017 07:00 AM, Philipp Zabel wrote:
> On Mon, 2017-03-20 at 12:08 +0000, Russell King - ARM Linux wrote:
>> On Mon, Mar 20, 2017 at 12:55:26PM +0100, Philipp Zabel wrote:
>>> The above paragraph suggests we skip any rectangles that are not
>>> supported. In our case that would be 3. and 4., since the CSI can't
>>> compose into a larger frame. I hadn't realised that the crop selection
>>> currently happens on the source pad.
>> I'd recommend viewing the documentation in its post-processed version,
>> because then you get the examples as pictures, and they say that a
>> picture is worth 1000 words.  See
>>
>>    https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/dev-subdev.html
>>
>> There is almost an exact example of what we're trying to do - it's
>> figure 4.6.  Here, we have a sink pad with a cropping rectangle on
>> the input, which is then scaled to a composition rectangle (there's
>> no bounds rectangle, and it's specified that in such a case the
>> top,left of the composition rectangle will always be 0,0 - see quote
>> below).
>>
>> Where it differs is that the example also supports source cropping
>> for two source pads.  We don't support that.
>>
>> The same document says:
>>
>>    Scaling support is optional. When supported by a subdev, the crop
>>    rectangle on the subdev's sink pad is scaled to the size configured
>>    using the
>>    :ref:`VIDIOC_SUBDEV_S_SELECTION <VIDIOC_SUBDEV_G_SELECTION>` IOCTL
>>    using ``V4L2_SEL_TGT_COMPOSE`` selection target on the same pad. If the
>>    subdev supports scaling but not composing, the top and left values are
>>    not used and must always be set to zero.
> Right, this sentence does imply that when scaling is supported, there
> must be a sink compose rectangle, even when composing is not.

Ok, this all makes consistent sense to me too. So:

- the CSI hardware cropping rectangle should be specified via the
   sink pad crop selection.

- the CSI hardware /2 downscaler should be specified via the
   sink pad compose selection.

- the final source pad rectangle is the same as the sink pad
   compose rectangle.

So that leaves only step 4 (source pad crop selection) as
unsupported.

Steve


> I have previously set up scaling like this:
>
> media-ctl --set-v4l2 "'ipu1_csi0_mux':2[fmt:UYVY2X8/1920x1080@1/60]"
> media-ctl --set-v4l2 "'ipu1_csi0':2[fmt:AYUV32/960x540@1/30]"
>
> Does this mean, it should work like this instead?
>
> media-ctl --set-v4l2 "'ipu1_csi0_mux':2[fmt:UYVY2X8/1920x1080@1/60]"
> media-ctl --set-v4l2 "'ipu1_csi0':0[fmt:UYVY2X8/1920x1080@1/60,compose:(0,0)/960x540]"
> media-ctl --set-v4l2 "'ipu1_csi0':2[fmt:AYUV32/960x540@1/30]"
>
> I suppose setting the source pad format should not be allowed to modify
> the sink compose rectangle.
>
> regards
> Philipp
>