linux-kernel - Re: [PATCH v7 06/10] media: i2c: ov9282: add hardware strobe signal v4l2 control

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Message-ID: <czhubfkhxayxbmn7hpgxjjqpylgo5c7jbrzobzxq65ruza2zfx@fhlxv2q63a5a>
Date: Mon, 8 Sep 2025 14:09:06 +0200
From: Richard Leitner <richard.leitner@...ux.dev>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Dave Stevenson <dave.stevenson@...pberrypi.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org, Hans Verkuil <hverkuil@...nel.org>
Subject: Re: [PATCH v7 06/10] media: i2c: ov9282: add hardware strobe signal
 v4l2 control


Hi Laurent,

thanks for your review!

On Sun, Sep 07, 2025 at 10:08:11PM +0200, Laurent Pinchart wrote:
> On Wed, Sep 03, 2025 at 08:58:04AM +0200, Richard Leitner wrote:
> > On Mon, Sep 01, 2025 at 11:57:15PM +0300, Sakari Ailus wrote:
> > > On Mon, Sep 01, 2025 at 05:05:11PM +0200, Richard Leitner wrote:
> > > > Add V4L2_CID_FLASH_HW_STROBE_SIGNAL enable/disable support using the
> > > > "strobe output enable" feature of the sensor.
> > > > 
> > > > All values are based on the OV9281 datasheet v1.53 (january 2019) and
> > > > tested using an ov9281 VisionComponents module.
> > > > 
> > > > Signed-off-by: Richard Leitner <richard.leitner@...ux.dev>
> > > > ---
> > > >  drivers/media/i2c/ov9282.c | 25 ++++++++++++++++++++++++-
> > > >  1 file changed, 24 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
> > > > index f42e0d439753e74d14e3a3592029e48f49234927..ff0f69f0dc3a2d0518806b9ea65c1b520b5c55fb 100644
> > > > --- a/drivers/media/i2c/ov9282.c
> > > > +++ b/drivers/media/i2c/ov9282.c
> > > > @@ -670,6 +670,23 @@ static int ov9282_set_ctrl_vflip(struct ov9282 *ov9282, int value)
> > > >  				current_val);
> > > >  }
> > > >  
> > > > +static int ov9282_set_ctrl_flash_hw_strobe_signal(struct ov9282 *ov9282, bool enable)
> > > > +{
> > > > +	u32 current_val;
> > > > +	int ret = ov9282_read_reg(ov9282, OV9282_REG_OUTPUT_ENABLE6, 1,
> > > > +				  &current_val);
> > > > +	if (ret)
> > > > +		return ret;
> > > 
> > > Please don't do assignments in variable declaration if that involves error
> > > handling.
> > 
> > Sure. Will fix that!
> > 
> > > > +
> > > > +	if (enable)
> > > > +		current_val |= OV9282_OUTPUT_ENABLE6_STROBE;
> > > > +	else
> > > > +		current_val &= ~OV9282_OUTPUT_ENABLE6_STROBE;
> > > > +
> > > > +	return ov9282_write_reg(ov9282, OV9282_REG_OUTPUT_ENABLE6, 1,
> > > > +				current_val);
> 
> It would be nice to cache the register value instead of reading it back.
> Regmap may help (and then the driver should use the CCI helpers). This
> can be done separately.
> 

Currently all set_ctrl calls in the ov9282 driver have this
read/modify/write pattern. As mentioned in the cover letter I'm planning
to migrate to cci helpers in a future series to keep the set smaller.
But if you prefer the migration in this series I can try to rebase on
it?

> > > > +}
> > > > +
> > > >  /**
> > > >   * ov9282_set_ctrl() - Set subdevice control
> > > >   * @ctrl: pointer to v4l2_ctrl structure
> > > > @@ -736,6 +753,9 @@ static int ov9282_set_ctrl(struct v4l2_ctrl *ctrl)
> > > >  		ret = ov9282_write_reg(ov9282, OV9282_REG_TIMING_HTS, 2,
> > > >  				       (ctrl->val + ov9282->cur_mode->width) >> 1);
> > > >  		break;
> > > > +	case V4L2_CID_FLASH_HW_STROBE_SIGNAL:
> > > > +		ret = ov9282_set_ctrl_flash_hw_strobe_signal(ov9282, ctrl->val);
> > > > +		break;
> > > >  	default:
> > > >  		dev_err(ov9282->dev, "Invalid control %d", ctrl->id);
> > > >  		ret = -EINVAL;
> > > > @@ -1326,7 +1346,7 @@ static int ov9282_init_controls(struct ov9282 *ov9282)
> > > >  	u32 lpfr;
> > > >  	int ret;
> > > >  
> > > > -	ret = v4l2_ctrl_handler_init(ctrl_hdlr, 10);
> > > > +	ret = v4l2_ctrl_handler_init(ctrl_hdlr, 11);
> > > >  	if (ret)
> > > >  		return ret;
> > > >  
> > > > @@ -1391,6 +1411,9 @@ static int ov9282_init_controls(struct ov9282 *ov9282)
> > > >  						OV9282_TIMING_HTS_MAX - mode->width,
> > > >  						1, hblank_min);
> > > >  
> > > > +	/* Flash/Strobe controls */
> > > > +	v4l2_ctrl_new_std(ctrl_hdlr, &ov9282_ctrl_ops, V4L2_CID_FLASH_HW_STROBE_SIGNAL, 0, 1, 1, 0);
> > > 
> > > This seems rather long.
> > 
> > It's exactly 100 chars wide, so from a policy point of view it should be
> > fine ;-). But I'm also fine with breaking it to 80 if you prefer?
> 
> That's the usual policy in V4L2, yes. 80 columns is the preferred soft
> limit.

So I should break this line in this case? Tbh I'm often unsure on
breaking on 80 or 100... Personally 100 is fine for me, but that's
"your" subsystem/driver, so I guess it's your descision ;-)

> 
> > > > +
> > > >  	ret = v4l2_fwnode_device_parse(ov9282->dev, &props);
> > > >  	if (!ret) {
> > > >  		/* Failure sets ctrl_hdlr->error, which we check afterwards anyway */
> > > > 
> 
> -- 
> Regards,
> 
> Laurent Pinchart

regards;rl