Message-ID: <9bd93a9c-27c6-335e-1c2f-23e12dba6c5f@xs4all.nl>
Date:   Mon, 8 May 2017 12:12:30 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Steve Longerbeam <slongerbeam@...il.com>, robh+dt@...nel.org,
        mark.rutland@....com, shawnguo@...nel.org, kernel@...gutronix.de,
        fabio.estevam@....com, linux@...linux.org.uk, mchehab@...nel.org,
        nick@...anahar.org, markus.heiser@...marIT.de,
        laurent.pinchart+renesas@...asonboard.com, bparrot@...com,
        geert@...ux-m68k.org, arnd@...db.de, sudipm.mukherjee@...il.com,
        minghsiu.tsai@...iatek.com, tiffany.lin@...iatek.com,
        jean-christophe.trotin@...com, horms+renesas@...ge.net.au,
        niklas.soderlund+renesas@...natech.se, robert.jarzmik@...e.fr,
        songjun.wu@...rochip.com, andrew-ct.chen@...iatek.com,
        gregkh@...uxfoundation.org, shuah@...nel.org,
        sakari.ailus@...ux.intel.com, pavel@....cz,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH] [media] imx: csi: retain current field order and
 colorimetry setting as default

On 05/08/2017 11:36 AM, Philipp Zabel wrote:
> Hi Hans,
> 
> On Mon, 2017-05-08 at 10:27 +0200, Hans Verkuil wrote:
>> Hi Philipp,
>>
>> Sorry for the very long delay, but I finally had some time to think about this.
> 
> Thank you for your thoughts.
> 
>> On 04/06/2017 03:55 PM, Philipp Zabel wrote:
>>> If the the field order is set to ANY in set_fmt, choose the currently
>>> set field order. If the colorspace is set to DEFAULT, choose the current
>>> colorspace.  If any of xfer_func, ycbcr_enc or quantization are set to
>>> DEFAULT, either choose the current setting, or the default setting for the
>>> new colorspace, if non-DEFAULT colorspace was given.
>>>
>>> This allows to let field order and colorimetry settings be propagated
>>> from upstream by calling media-ctl on the upstream entity source pad,
>>> and then call media-ctl on the sink pad to manually set the input frame
>>> interval, without changing the already set field order and colorimetry
>>> information.
>>>
>>> Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
>>> ---
>>> This is based on imx-media-staging-md-v14, and it is supposed to allow
>>> configuring the pipeline with media-ctl like this:
>>>
>>> 1) media-ctl --set-v4l2 "'tc358743 1-000f':0[fmt:UYVY8_1X16/1920x1080]"
>>> 2) media-ctl --set-v4l2 "'imx6-mipi-csi2':1[fmt:UYVY8_1X16/1920x108]"
>>> 3) media-ctl --set-v4l2 "'ipu1_csi0_mux':2[fmt:UYVY8_1X16/1920x1080]"
>>> 4) media-ctl --set-v4l2 "'ipu1_csi0':0[fmt:UYVY8_1X16/1920x1080@...0]"
>>> 5) media-ctl --set-v4l2 "'ipu1_csi0':2[fmt:AYUV32/1920x1080@...0]"
>>>
>>> Without having step 4) overwrite the colorspace and field order set on
>>> 'ipu1_csi0':0 by the propagation in step 3).
>>> ---
>>>  drivers/staging/media/imx/imx-media-csi.c | 34 +++++++++++++++++++++++++++++++
>>>  1 file changed, 34 insertions(+)
>>>
>>> diff --git a/drivers/staging/media/imx/imx-media-csi.c b/drivers/staging/media/imx/imx-media-csi.c
>>> index 64dc454f6b371..d94ce1de2bf05 100644
>>> --- a/drivers/staging/media/imx/imx-media-csi.c
>>> +++ b/drivers/staging/media/imx/imx-media-csi.c
>>> @@ -1325,6 +1325,40 @@ static int csi_set_fmt(struct v4l2_subdev *sd,
>>>  	csi_try_fmt(priv, sensor, cfg, sdformat, crop, compose, &cc);
>>>  
>>>  	fmt = __csi_get_fmt(priv, cfg, sdformat->pad, sdformat->which);
>>> +
>>> +	/* Retain current field setting as default */
>>> +	if (sdformat->format.field == V4L2_FIELD_ANY)
>>> +		sdformat->format.field = fmt->field;
>>
>> This is OK.
> 
> Would this be a "may" or a "should"? As in,
> "If SUBDEV_S_FMT is called with field == ANY, the driver may/should set
> field to the previously configured interlacing field order".

To quote the FIELD_ANY documentation:

file:///home/hans/work/src/v4l/media-git/Documentation/output/html/uapi/v4l/field-order.html#field-order

"Drivers must never return V4L2_FIELD_ANY."

How a driver replaces FIELD_ANY is something that I am not sure should be explicitly
stated in the documentation. In many cases there is only one choice (usually FIELD_NONE).

In cases like this I think your proposed rule is a good recommendation. I would probably
phrase it like that.

> What would be the correct place to document this behaviour?
> Documentation/media/uapi/v4l/vidioc-subdev-g-fmt.rst?

Yes.

> 
>>> +	/* Retain current colorspace setting as default */
>>> +	if (sdformat->format.colorspace == V4L2_COLORSPACE_DEFAULT) {
>>> +		sdformat->format.colorspace = fmt->colorspace;
>>> +		if (sdformat->format.xfer_func == V4L2_XFER_FUNC_DEFAULT)
>>> +			sdformat->format.xfer_func = fmt->xfer_func;
>>> +		if (sdformat->format.ycbcr_enc == V4L2_YCBCR_ENC_DEFAULT)
>>> +			sdformat->format.ycbcr_enc = fmt->ycbcr_enc;
>>> +		if (sdformat->format.quantization == V4L2_QUANTIZATION_DEFAULT)
>>> +			sdformat->format.quantization = fmt->quantization;
>>
>> If sdformat->format.colorspace == V4L2_COLORSPACE_DEFAULT, then you can just copy
>> all four fields from fmt to sdformat->format. The other three fields are meaningless
>> when colorspace == V4L2_COLORSPACE_DEFAULT.
> 
> Ok, good. Ignoring the transfer function / YCbCr encoding / quantization
> range fields when colorspace is DEFAULT would simplify this part to:
> 
> 	if (sdformat->format.colorspace == V4L2_COLORSPACE_DEFAULT) {
> 		sdformat->format.colorspace = fmt->colorspace;
> 		sdformat->format.xfer_func = fmt->xfer_func;
> 		sdformat->format.ycbcr_enc = fmt->ycbcr_enc;
> 		sdformat->format.quantization = fmt->quantization;
> 	}
> 
> Is that expectation already written down somewhere? If not, should we
> add it to Documentation/media/uapi/v4l/pixfmt-006.rst?

I don't think it is written down. It would be a good idea to make this
explicit.

> 
>>> +	} else {
>>> +		if (sdformat->format.xfer_func == V4L2_XFER_FUNC_DEFAULT) {
>>> +			sdformat->format.xfer_func =
>>> +				V4L2_MAP_XFER_FUNC_DEFAULT(
>>> +						sdformat->format.colorspace);
>>> +		}
>>> +		if (sdformat->format.ycbcr_enc == V4L2_YCBCR_ENC_DEFAULT) {
>>> +			sdformat->format.ycbcr_enc =
>>> +				V4L2_MAP_YCBCR_ENC_DEFAULT(
>>> +						sdformat->format.colorspace);
>>> +		}
>>> +		if (sdformat->format.quantization == V4L2_QUANTIZATION_DEFAULT) {
>>> +			sdformat->format.quantization =
>>> +				V4L2_MAP_QUANTIZATION_DEFAULT(
>>> +						cc->cs != IPUV3_COLORSPACE_YUV,
>>> +						sdformat->format.colorspace,
>>> +						sdformat->format.ycbcr_enc);
>>> +		}
>>
>> Is this needed for validation? Currently these fields play no role in the
>> default link validation. Which I think is actually the right thing to do,
>> unless the subdev can do actual colorspace conversion.
> 
> The CSI subdevice can't do colorspace conversion, but exactly the same
> applies to the IC subdevices, which can. Also I'd like this information
> to be correct, as the /dev/videoX capture device takes its colorspace
> information from the CSI source pad.
> 
> The problem I wanted to solve here initially was that if the colorspace
> information was previously set correctly:
> 
>   media-ctl --set-v4l2 "'ipu1_csi0':0[fmt:UYVY8_1X16/1920x1080@...0 colorspace:rec709 xfer:709 ycbcr:709 quantization:lim-range]"
>     ->
> 	V4L2_COLORSPACE_REC709
> 	V4L2_XFER_FUNC_709
> 	V4L2_YCBCR_ENC_709
> 	V4L2_QUANTIZATION_LIMITED_RANGE
> 
> A later media-ctl call to just change the frame interval would overwrite the colorspace information:
> 
>   media-ctl --set-v4l2 "'ipu1_csi0':0[fmt:UYVY8_1X16/1920x1080@...0]"
>     ->
> 	V4L2_COLORSPACE_DEFAULT
> 	V4L2_XFER_FUNC_DEFAULT
> 	V4L2_YCBCR_ENC_DEFAULT
> 	V4L2_QUANTIZATION_DEFAULT

Not anymore since if media-ctl sets colorspace to DEFAULT, then it will just copy
the last configuration.

If media-ctl sets colorspace to a non-DEFAULT value, then I assume that it is a
new explicitly defined colorspace.

> 
>> I would just drop the whole 'else' here.
> 
> That would allow to set the actual colorspace information reported by
> SUBDEV_G_FMT on both sink and source pads (and by extension, the
> colorspace information reported by G_FMT on /dev/videoX) to
> V4L2_{XFER_FUNC,YCBCR_ENC,QUANTIZATION}_DEFAULT.
> 
>   media-ctl --set-v4l2 "'ipu1_csi0':0[fmt:UYVY8_1X16/1920x1080 colorspace:rec709]"
>     ->
> 	V4L2_COLORSPACE_REC709
> 	V4L2_XFER_FUNC_DEFAULT
> 	V4L2_YCBCR_ENC_DEFAULT
> 	V4L2_QUANTIZATION_DEFAULT
> 
> I suppose that is acceptable as given the colorspace, the other DEFAULT
> values have a unique meaning, but wouldn't it be nicer to show userspace
> what these default inputs actually map to?

Good question. Right now this isn't done in other drivers.

I have been struggling with this question myself. My problem is that I don't like
to have to copy this code in every driver. Ideally this should be handled in the
v4l2 core, but I am not sure if all the required information is available there.

I would postpone this, and look at this in a separate patch.

>> Actually, wouldn't it be better to always just copy this information from
>> fmt? This subdev doesn't do any colorspace conversion, it just passes on
>> this information. I.e., you can't set it in any meaningful way.
> 
> csi_set_fmt on the sink pad is the function that actually sets fmt in
> the first place. If we always copy colorspace information from fmt, it
> can't be set to the correct value at all.

Yes, sorry about that. Ignore that comment.

Regards,

	Hans

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