linux-kernel - Re: [PATCH 1/4] media: mt9m111: add V4L2_CID_PIXEL

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Message-ID: <20220819075615.a3nuakrac54kn7t3@pengutronix.de>
Date:   Fri, 19 Aug 2022 09:56:15 +0200
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     Jacopo Mondi <jacopo@...ndi.org>
Cc:     mchehab@...nel.org, sakari.ailus@...ux.intel.com,
        laurent.pinchart+renesas@...asonboard.com,
        jacopo+renesas@...ndi.org, akinobu.mita@...il.com,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH 1/4] media: mt9m111: add V4L2_CID_PIXEL_RATE support

Hi Jacopo,

On 22-08-18, Jacopo Mondi wrote:
> Hi Marco
> 
> On Thu, Aug 18, 2022 at 04:47:09PM +0200, Marco Felsch wrote:
> > Add support to report the PIXEL_RATE so a host or bridge device can ask
> > the sensor.
> >
> > Signed-off-by: Marco Felsch <m.felsch@...gutronix.de>
> > ---
> >  drivers/media/i2c/mt9m111.c | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/i2c/mt9m111.c b/drivers/media/i2c/mt9m111.c
> > index afc86efa9e3e..cdaf283e1309 100644
> > --- a/drivers/media/i2c/mt9m111.c
> > +++ b/drivers/media/i2c/mt9m111.c
> > @@ -908,6 +908,8 @@ static int mt9m111_s_ctrl(struct v4l2_ctrl *ctrl)
> >  		return mt9m111_set_test_pattern(mt9m111, ctrl->val);
> >  	case V4L2_CID_COLORFX:
> >  		return mt9m111_set_colorfx(mt9m111, ctrl->val);
> > +	case V4L2_CID_PIXEL_RATE:
> > +		return 0;
> 
> By default PIXEL_RATE is read-only.
> Do you get a call to s_ctrl for it ?

You're absolutly right, we don't need to do this.

> >  	}
> >
> >  	return -EINVAL;
> > @@ -1249,6 +1251,7 @@ static int mt9m111_probe(struct i2c_client *client)
> >  {
> >  	struct mt9m111 *mt9m111;
> >  	struct i2c_adapter *adapter = client->adapter;
> > +	unsigned long mclk_rate;
> >  	int ret;
> >
> >  	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WORD_DATA)) {
> > @@ -1271,6 +1274,13 @@ static int mt9m111_probe(struct i2c_client *client)
> >  	if (IS_ERR(mt9m111->clk))
> >  		return PTR_ERR(mt9m111->clk);
> >
> > +	ret = clk_prepare_enable(mt9m111->clk);
> > +	if (ret < 0)
> > +		return ret;
> > +
> 
> Do you need to enable clock to read its rate ?

Yes, accroding the API [1].

[1] https://elixir.bootlin.com/linux/v6.0-rc1/source/include/linux/clk.h#L682

> > +	mclk_rate = clk_get_rate(mt9m111->clk);
> > +	clk_disable_unprepare(mt9m111->clk);
> > +
> >  	mt9m111->regulator = devm_regulator_get(&client->dev, "vdd");
> >  	if (IS_ERR(mt9m111->regulator)) {
> >  		dev_err(&client->dev, "regulator not found: %ld\n",
> > @@ -1285,7 +1295,7 @@ static int mt9m111_probe(struct i2c_client *client)
> >  	mt9m111->subdev.flags |= V4L2_SUBDEV_FL_HAS_DEVNODE |
> >  				 V4L2_SUBDEV_FL_HAS_EVENTS;
> >
> > -	v4l2_ctrl_handler_init(&mt9m111->hdl, 7);
> > +	v4l2_ctrl_handler_init(&mt9m111->hdl, 8);
> >  	v4l2_ctrl_new_std(&mt9m111->hdl, &mt9m111_ctrl_ops,
> >  			V4L2_CID_VFLIP, 0, 1, 1, 0);
> >  	v4l2_ctrl_new_std(&mt9m111->hdl, &mt9m111_ctrl_ops,
> > @@ -1309,6 +1319,9 @@ static int mt9m111_probe(struct i2c_client *client)
> >  				BIT(V4L2_COLORFX_NEGATIVE) |
> >  				BIT(V4L2_COLORFX_SOLARIZATION)),
> >  			V4L2_COLORFX_NONE);
> > +	v4l2_ctrl_new_std(&mt9m111->hdl, &mt9m111_ctrl_ops, V4L2_CID_PIXEL_RATE,
> > +			  mclk_rate, mclk_rate, 1, mclk_rate);
> > +
> 
> I don't have a datasheet but it seems a little weird that the mclk
> frequency is the same as the pixel clock rate ?

I see your confusion here. I can only speak for the MT9M131 device which
is covered by this driver as well. This device is composed of a
internal-sensor and a internal-isp. The internal-sensor is clocked by
mclk/2 but the final image device/sensor output-fifo is clocked by mclk.
There are options to devide the output clock as well, but these options
are not enabled yet. So yes, the pixel clock rate == mclk rate. To avoid
confusion I could rename the mclk_rate to extclk_rate but then clock
request is not 100% correct since we are requesting a "mclk", this
should be "extclk".

Regards,
  Marco

> >  	mt9m111->subdev.ctrl_handler = &mt9m111->hdl;
> >  	if (mt9m111->hdl.error) {
> >  		ret = mt9m111->hdl.error;
> > --
> > 2.30.2
> >
>