linux-kernel - Re: [PATCH v7 07/10] media: i2c: ov9282: add strobe

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Message-ID: <aLYISb07ziGDmFGS@kekkonen.localdomain>
Date: Mon, 1 Sep 2025 23:55:37 +0300
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Richard Leitner <richard.leitner@...ux.dev>
Cc: Dave Stevenson <dave.stevenson@...pberrypi.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-leds@...r.kernel.org, Hans Verkuil <hverkuil@...nel.org>
Subject: Re: [PATCH v7 07/10] media: i2c: ov9282: add strobe_duration v4l2
 control

Hi Richard,

On Mon, Sep 01, 2025 at 05:05:12PM +0200, Richard Leitner wrote:
> Add V4L2_CID_FLASH_DURATION support using the "strobe_frame_span"
> feature of the sensor. This is implemented by transforming the given µs
> value by an interpolated formula to a "span step width" value and
> writing it to register PWM_CTRL_25, PWM_CTRL_26, PWM_CTRL_27,
> PWM_CTRL_28 (0x3925, 0x3926, 0x3927, 0x3928).
> 
> The maximum control value is set to the period of the current default
> framerate.
> 
> All register values are based on the OV9281 datasheet v1.53 (jan 2019)
> and tested using an ov9281 VisionComponents module.
> 
> Signed-off-by: Richard Leitner <richard.leitner@...ux.dev>
> ---
>  drivers/media/i2c/ov9282.c | 31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
> index ff0f69f0dc3a2d0518806b9ea65c1b520b5c55fb..c405e3411daf37cf98d5af3535702f8321394af5 100644
> --- a/drivers/media/i2c/ov9282.c
> +++ b/drivers/media/i2c/ov9282.c
> @@ -97,6 +97,10 @@
>  #define OV9282_REG_MIPI_CTRL00	0x4800
>  #define OV9282_GATED_CLOCK	BIT(5)
>  
> +/* Flash/Strobe control registers */
> +#define OV9282_REG_FLASH_DURATION	0x3925
> +#define OV9282_FLASH_DURATION_DEFAULT	0x0000001a
> +
>  /* Input clock rate */
>  #define OV9282_INCLK_RATE	24000000
>  
> @@ -687,6 +691,25 @@ static int ov9282_set_ctrl_flash_hw_strobe_signal(struct ov9282 *ov9282, bool en
>  				current_val);
>  }
>  
> +static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, u32 value)
> +{
> +	/*
> +	 * Calculate "strobe_frame_span" increments from a given value (µs).
> +	 * This is quite tricky as "The step width of shift and span is
> +	 * programmable under system clock domain.", but it's not documented
> +	 * how to program this step width (at least in the datasheet available
> +	 * to the author at time of writing).
> +	 * The formula below is interpolated from different modes/framerates
> +	 * and should work quite well for most settings.
> +	 */
> +	u32 val = value * 192 / (ov9282->cur_mode->width + ov9282->hblank_ctrl->val);
> +
> +	ov9282_write_reg(ov9282, OV9282_REG_FLASH_DURATION, 1, (val >> 24) & 0xff);
> +	ov9282_write_reg(ov9282, OV9282_REG_FLASH_DURATION + 1, 1, (val >> 16) & 0xff);
> +	ov9282_write_reg(ov9282, OV9282_REG_FLASH_DURATION + 2, 1, (val >> 8) & 0xff);
> +	return ov9282_write_reg(ov9282, OV9282_REG_FLASH_DURATION + 3, 1, val & 0xff);

The bitwise and operation is redundant.

Could you do this in a single write?

Also error handling is (largely) missing.

> +}
> +
>  /**
>   * ov9282_set_ctrl() - Set subdevice control
>   * @ctrl: pointer to v4l2_ctrl structure
> @@ -756,6 +779,9 @@ static int ov9282_set_ctrl(struct v4l2_ctrl *ctrl)
>  	case V4L2_CID_FLASH_HW_STROBE_SIGNAL:
>  		ret = ov9282_set_ctrl_flash_hw_strobe_signal(ov9282, ctrl->val);
>  		break;
> +	case V4L2_CID_FLASH_DURATION:
> +		ret = ov9282_set_ctrl_flash_duration(ov9282, ctrl->val);
> +		break;
>  	default:
>  		dev_err(ov9282->dev, "Invalid control %d", ctrl->id);
>  		ret = -EINVAL;
> @@ -1346,7 +1372,7 @@ static int ov9282_init_controls(struct ov9282 *ov9282)
>  	u32 lpfr;
>  	int ret;
>  
> -	ret = v4l2_ctrl_handler_init(ctrl_hdlr, 11);
> +	ret = v4l2_ctrl_handler_init(ctrl_hdlr, 12);
>  	if (ret)
>  		return ret;
>  
> @@ -1414,6 +1440,9 @@ static int ov9282_init_controls(struct ov9282 *ov9282)
>  	/* Flash/Strobe controls */
>  	v4l2_ctrl_new_std(ctrl_hdlr, &ov9282_ctrl_ops, V4L2_CID_FLASH_HW_STROBE_SIGNAL, 0, 1, 1, 0);
>  
> +	v4l2_ctrl_new_std(ctrl_hdlr, &ov9282_ctrl_ops, V4L2_CID_FLASH_DURATION,
> +			  0, 13900, 1, 8);
> +
>  	ret = v4l2_fwnode_device_parse(ov9282->dev, &props);
>  	if (!ret) {
>  		/* Failure sets ctrl_hdlr->error, which we check afterwards anyway */
> 

-- 
Regards,

Sakari Ailus