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

[Stefan Riedmüller]

Hi Laurent,

On 30.09.20 13:42, Laurent Pinchart wrote:
> Hi Stefan,
>
> Thank you for the patch.
>
> On Wed, Sep 30, 2020 at 12:51:29PM +0200, Stefan Riedmueller wrote:
> > From: Christian Hemp <c.hemp@xxxxxxxxx>
> >
> > 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.

Does this clarify things? Maybe the description in the commit message is not 
accurate enough or did I get something wrong?

Thanks,
Stefan

> > Signed-off-by: Christian Hemp <c.hemp@xxxxxxxxx>
> > [jlu@xxxxxxxxxxxxxx: simplified by dropping v4l2_colorspace handling]
> > Signed-off-by: Jan Luebbe <jlu@xxxxxxxxxxxxxx>
> > Signed-off-by: Stefan Riedmueller <s.riedmueller@xxxxxxxxx>
> > ---
> > 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;