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

From: Laurent Pinchart
Date: Thu Oct 01 2020 - 19:54:19 EST

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@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.

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.

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@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;

--
Regards,

Laurent Pinchart