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Subject: Re: [PATCH v2 3/6] media: mt9m111: add support to select formats and
 fps for {Q,SXGA}
To: Sakari Ailus <sakari.ailus@iki.fi>,
        Marco Felsch <m.felsch@pengutronix.de>
Cc: mchehab@kernel.org, sakari.ailus@linux.intel.com,
        robh+dt@kernel.org, mark.rutland@arm.com,
        enrico.scholz@sigma-chemnitz.de, akinobu.mita@gmail.com,
        linux-media@vger.kernel.org, devicetree@vger.kernel.org,
        Michael Grzeschik <m.grzeschik@pengutronix.de>,
        graphics@pengutronix.de
References: <20181029182410.18783-1-m.felsch@pengutronix.de>
 <20181029182410.18783-4-m.felsch@pengutronix.de>
 <20181116132610.54elo2dqsrrlydlh@valkosipuli.retiisi.org.uk>
From: Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <e28d74c2-d2de-6450-d572-6d691b7416c7@xs4all.nl>
Date: Fri, 16 Nov 2018 14:31:01 +0100
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On 11/16/2018 02:26 PM, Sakari Ailus wrote:
> Hi Marco, Michael,
> 
> On Mon, Oct 29, 2018 at 07:24:07PM +0100, Marco Felsch wrote:
>> From: Michael Grzeschik <m.grzeschik@pengutronix.de>
>>
>> This patch implements the framerate selection using the skipping and
>> readout power-modi features. The power-modi cut the framerate by half
>> and each context has an independent selection bit. The same applies to
>> the 2x skipping feature.
>>
>> Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
>> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
>>
>> ---
>> Changelog
>>
>> v2:
>> - fix updating read mode register, use mt9m111_reg_mask() to update the
>>   relevant bits only. For this purpose add reg_mask field to
>>   struct mt9m111_mode_info.
>>
>>  drivers/media/i2c/mt9m111.c | 163 ++++++++++++++++++++++++++++++++++++
>>  1 file changed, 163 insertions(+)
>>
>> diff --git a/drivers/media/i2c/mt9m111.c b/drivers/media/i2c/mt9m111.c

<snip>

>> +static const struct mt9m111_mode_info *
>> +mt9m111_find_mode(struct mt9m111 *mt9m111, unsigned int req_fps,
>> +		  unsigned int width, unsigned int height)
>> +{
>> +	const struct mt9m111_mode_info *mode;
>> +	struct v4l2_rect *sensor_rect = &mt9m111->rect;
>> +	unsigned int gap, gap_best = (unsigned int) -1;
>> +	int i, best_gap_idx = 1;
>> +
>> +	/* find best matched fps */
>> +	for (i = 0; i < MT9M111_NUM_MODES; i++) {
>> +		unsigned int fps = mt9m111_mode_data[i].max_fps;
>> +
>> +		gap = abs(fps - req_fps);
>> +		if (gap < gap_best) {
>> +			best_gap_idx = i;
>> +			gap_best = gap;
>> +		}
> 
> Could you use v4l2_find_nearest_size() instead?
> 
> Also see below...
> 
>> +	}
>> +
>> +	/*
>> +	 * Use context a/b default timing values instead of calculate blanking
>> +	 * timing values.
>> +	 */
>> +	mode = &mt9m111_mode_data[best_gap_idx];
>> +	mt9m111->ctx = (best_gap_idx == MT9M111_MODE_QSXGA_30FPS) ? &context_a :
>> +								    &context_b;
>> +
>> +	/*
>> +	 * Check if current settings support the fps because fps selection is
>> +	 * based on the row/col skipping mechanism which has some restriction.
>> +	 */
>> +	if (sensor_rect->width != mode->sensor_w ||
>> +	    sensor_rect->height != mode->sensor_h ||
>> +	    width > mode->max_image_w ||
>> +	    height > mode->max_image_h) {
>> +		/* reset sensor window size */
>> +		mt9m111->rect.left = MT9M111_MIN_DARK_COLS;
>> +		mt9m111->rect.top = MT9M111_MIN_DARK_ROWS;
>> +		mt9m111->rect.width = mode->sensor_w;
>> +		mt9m111->rect.height = mode->sensor_h;
>> +
>> +		/* reset image size */
>> +		mt9m111->width = mode->max_image_w;
>> +		mt9m111->height = mode->max_image_h;
>> +
>> +		dev_warn(mt9m111->subdev.dev,
>> +			 "Warning: update image size %dx%d[%dx%d] -> %dx%d[%dx%d]\n",
>> +			 sensor_rect->width, sensor_rect->height, width, height,
>> +			 mode->sensor_w, mode->sensor_h, mode->max_image_w,
>> +			 mode->max_image_h);
> 
> I wouldn't expect requesting a particular frame rate to change the sensor
> format. The other way around is definitely fine though.
> 
> Cc Hans.

I agree with Sakari. Changing the framerate should never change the format.
When you enumerate framerates those framerates are the allowed framerates
for the mediabus format and the resolution. So changing the framerate should
never modify the format or resolution. Instead, the framerate should be
mapped to a framerate that is valid for the format/resolution combo.

Regards,

	Hans