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

From: "Stefan Riedmüller" <s.riedmueller@phytec.de>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
	Christian Hemp <c.hemp@phytec.de>,
	Jan Luebbe <jlu@pengutronix.de>
Subject: Re: [PATCH v2 1/5] media: mt9p031: Add support for 8 bit and 10 bit formats
Date: Thu, 1 Oct 2020 11:07:00 +0200	[thread overview]
Message-ID: <eacb7df5-bc68-3047-b893-4c1ba4975278@phytec.de> (raw)
In-Reply-To: <20200930114231.GH5689@pendragon.ideasonboard.com>

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@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.

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@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;
> 