Re: [PATCH v2 1/5] media: mt9p031: Add support for 8 bit and 10 bit formats

["Stefan Riedmüller" <s.riedmueller@phytec.de>]

Hi Laurent,

On 02.10.20 01:53, Laurent Pinchart wrote:
> Hi Stefan,
> 
> On Thu, Oct 01, 2020 at 11:07:00AM +0200, Stefan Riedmüller wrote:
>> On 30.09.20 13:42, Laurent Pinchart wrote:
>>> On Wed, Sep 30, 2020 at 12:51:29PM +0200, Stefan Riedmueller wrote:
>>>> From: Christian Hemp <c.hemp@phytec.de>
>>>>
>>>> Aside from 12 bit monochrome or color format the sensor implicitly
>>>> supports 10 and 8 bit formats as well by simply dropping the
>>>> corresponding LSBs.
>>>
>>> That's not how it should work though. If you set the format on
>>> MEDIA_BUS_FMT_SGRBG8_1X8 through the pipeline for instance, you will end
>>> up capturing the 8 LSB, not the 8 MSB.
>>>
>>> What's your use case for this ?
>>
>> I use this sensor in combination with an i.MX 6 and i.MX 6UL. When the
>> sensor is connected with 12 bit (or 10 bit on the i.MX 6UL) and I set
>> MEDIA_BUS_FMT_SGRBG8_1X8 through the pipeline the CSI interface drops the
>> unused 4 LSB (or 2 LSB on the i.MX 6UL) so I get the 8 MSB from my 12 bit
>> sensor.
> 
> Is that the PIXEL_BIT bit in CSI_CSICR1 for the i.MX6UL ? If so I think
> this should be handled in the imx7-media-csi driver. You could set the
> format to MEDIA_BUS_FMT_SGRBG10_1X10 on the sink pad of the CSI and to
> MEDIA_BUS_FMT_SGRBG8_1X8 on the source pad to configure this. I don't
> think the sensor driver should be involved, otherwise we'd have to patch
> all sensor drivers. From a sensor point of view, it outputs 12-bit
> Bayer, not 8-bit.

Ah, I had it wrong. What you say makes total sense. I will take another look 
at it and also try to work your suggestion from below in.

Thanks,
Stefan

> 
> Now there's a caveat. When used with the i.MX6UL, I assume you connected
> D[11:2] of the sensor to D[9:0] of the i.MX6UL, right ? The i.MX6UL
> doesn't support 12-bit inputs, so it should accept
> MEDIA_BUS_FMT_SGRBG12_1X12 on its sink pad. In this case, as D[1:0] of
> the sensor are left unconnected, I think you should set data-shift to 2
> and bus-width to 10 in DT on the sensor side. The MT9P031 driver should
> parse that, and output MEDIA_BUS_FMT_SGRBG10_1X10 instead of
> MEDIA_BUS_FMT_SGRBG12_1X12 in that case.
> 
>> Does this clarify things? Maybe the description in the commit message is not
>> accurate enough or did I get something wrong?
>>
>>>> Signed-off-by: Christian Hemp <c.hemp@phytec.de>
>>>> [jlu@pengutronix.de: simplified by dropping v4l2_colorspace handling]
>>>> Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
>>>> Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
>>>> ---
>>>> Changes in v2:
>>>>    - Use unsigned int for num_fmts and loop variable in find_datafmt
>>>>    - Remove superfluous const qualifier from find_datafmt
>>>> ---
>>>>    drivers/media/i2c/mt9p031.c | 50 +++++++++++++++++++++++++++++--------
>>>>    1 file changed, 40 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/media/i2c/mt9p031.c b/drivers/media/i2c/mt9p031.c
>>>> index dc23b9ed510a..2e6671ef877c 100644
>>>> --- a/drivers/media/i2c/mt9p031.c
>>>> +++ b/drivers/media/i2c/mt9p031.c
>>>> @@ -116,6 +116,18 @@ enum mt9p031_model {
>>>>    	MT9P031_MODEL_MONOCHROME,
>>>>    };
>>>>    
>>>> +static const u32 mt9p031_color_fmts[] = {
>>>> +	MEDIA_BUS_FMT_SGRBG8_1X8,
>>>> +	MEDIA_BUS_FMT_SGRBG10_1X10,
>>>> +	MEDIA_BUS_FMT_SGRBG12_1X12,
>>>> +};
>>>> +
>>>> +static const u32 mt9p031_monochrome_fmts[] = {
>>>> +	MEDIA_BUS_FMT_Y8_1X8,
>>>> +	MEDIA_BUS_FMT_Y10_1X10,
>>>> +	MEDIA_BUS_FMT_Y12_1X12,
>>>> +};
>>>> +
>>>>    struct mt9p031 {
>>>>    	struct v4l2_subdev subdev;
>>>>    	struct media_pad pad;
>>>> @@ -138,6 +150,9 @@ struct mt9p031 {
>>>>    	struct v4l2_ctrl *blc_auto;
>>>>    	struct v4l2_ctrl *blc_offset;
>>>>    
>>>> +	const u32 *fmts;
>>>> +	unsigned int num_fmts;
>>>> +
>>>>    	/* Registers cache */
>>>>    	u16 output_control;
>>>>    	u16 mode2;
>>>> @@ -148,6 +163,17 @@ static struct mt9p031 *to_mt9p031(struct v4l2_subdev *sd)
>>>>    	return container_of(sd, struct mt9p031, subdev);
>>>>    }
>>>>    
>>>> +static u32 mt9p031_find_datafmt(struct mt9p031 *mt9p031, u32 code)
>>>> +{
>>>> +	unsigned int i;
>>>> +
>>>> +	for (i = 0; i < mt9p031->num_fmts; i++)
>>>> +		if (mt9p031->fmts[i] == code)
>>>> +			return mt9p031->fmts[i];
>>>> +
>>>> +	return mt9p031->fmts[mt9p031->num_fmts-1];
>>>> +}
>>>> +
>>>>    static int mt9p031_read(struct i2c_client *client, u8 reg)
>>>>    {
>>>>    	return i2c_smbus_read_word_swapped(client, reg);
>>>> @@ -476,10 +502,11 @@ static int mt9p031_enum_mbus_code(struct v4l2_subdev *subdev,
>>>>    {
>>>>    	struct mt9p031 *mt9p031 = to_mt9p031(subdev);
>>>>    
>>>> -	if (code->pad || code->index)
>>>> +	if (code->pad || code->index >= mt9p031->num_fmts)
>>>>    		return -EINVAL;
>>>>    
>>>> -	code->code = mt9p031->format.code;
>>>> +	code->code = mt9p031->fmts[code->index];
>>>> +
>>>>    	return 0;
>>>>    }
>>>>    
>>>> @@ -573,6 +600,8 @@ static int mt9p031_set_format(struct v4l2_subdev *subdev,
>>>>    	__format->width = __crop->width / hratio;
>>>>    	__format->height = __crop->height / vratio;
>>>>    
>>>> +	__format->code = mt9p031_find_datafmt(mt9p031, format->format.code);
>>>> +
>>>>    	format->format = *__format;
>>>>    
>>>>    	return 0;
>>>> @@ -951,10 +980,7 @@ static int mt9p031_open(struct v4l2_subdev *subdev, struct v4l2_subdev_fh *fh)
>>>>    
>>>>    	format = v4l2_subdev_get_try_format(subdev, fh->pad, 0);
>>>>    
>>>> -	if (mt9p031->model == MT9P031_MODEL_MONOCHROME)
>>>> -		format->code = MEDIA_BUS_FMT_Y12_1X12;
>>>> -	else
>>>> -		format->code = MEDIA_BUS_FMT_SGRBG12_1X12;
>>>> +	format->code = mt9p031_find_datafmt(mt9p031, 0);
>>>>    
>>>>    	format->width = MT9P031_WINDOW_WIDTH_DEF;
>>>>    	format->height = MT9P031_WINDOW_HEIGHT_DEF;
>>>> @@ -1121,10 +1147,14 @@ static int mt9p031_probe(struct i2c_client *client,
>>>>    	mt9p031->crop.left = MT9P031_COLUMN_START_DEF;
>>>>    	mt9p031->crop.top = MT9P031_ROW_START_DEF;
>>>>    
>>>> -	if (mt9p031->model == MT9P031_MODEL_MONOCHROME)
>>>> -		mt9p031->format.code = MEDIA_BUS_FMT_Y12_1X12;
>>>> -	else
>>>> -		mt9p031->format.code = MEDIA_BUS_FMT_SGRBG12_1X12;
>>>> +	if (mt9p031->model == MT9P031_MODEL_MONOCHROME) {
>>>> +		mt9p031->fmts = mt9p031_monochrome_fmts;
>>>> +		mt9p031->num_fmts = ARRAY_SIZE(mt9p031_monochrome_fmts);
>>>> +	} else {
>>>> +		mt9p031->fmts = mt9p031_color_fmts;
>>>> +		mt9p031->num_fmts = ARRAY_SIZE(mt9p031_color_fmts);
>>>> +	}
>>>> +	mt9p031->format.code = mt9p031_find_datafmt(mt9p031, 0);
>>>>    
>>>>    	mt9p031->format.width = MT9P031_WINDOW_WIDTH_DEF;
>>>>    	mt9p031->format.height = MT9P031_WINDOW_HEIGHT_DEF;
>