linux-kernel - Re: [PATCH v8 7/8] media: i2c: ov9282: implement try_ctrl for strobe

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Message-ID: <aRGaZptpBRq_iga-@kekkonen.localdomain>
Date: Mon, 10 Nov 2025 09:55:18 +0200
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 v8 7/8] media: i2c: ov9282: implement try_ctrl for
 strobe_duration

Hi Richard,

On Tue, Nov 04, 2025 at 03:30:58PM +0100, Richard Leitner wrote:
> As the granularity of the hardware supported values is lower than the
> control value, implement a try_ctrl() function for
> V4L2_CID_FLASH_DURATION. This function calculates the nearest possible
> µs strobe duration for the given value and returns it back to the
> caller.
> 
> Signed-off-by: Richard Leitner <richard.leitner@...ux.dev>
> ---
>  drivers/media/i2c/ov9282.c | 55 +++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 52 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
> index 26296dc1d1b95..7aa74feb3ee44 100644
> --- a/drivers/media/i2c/ov9282.c
> +++ b/drivers/media/i2c/ov9282.c
> @@ -128,6 +128,8 @@
>  #define OV9282_REG_MIN		0x00
>  #define OV9282_REG_MAX		0xfffff
>  
> +#define OV9282_STROBE_SPAN_FACTOR	192
> +
>  static const char * const ov9282_supply_names[] = {
>  	"avdd",		/* Analog power */
>  	"dovdd",	/* Digital I/O power */
> @@ -691,9 +693,8 @@ static int ov9282_set_ctrl_flash_strobe_oe(struct ov9282 *ov9282, bool enable)
>  	return ov9282_write_reg(ov9282, OV9282_REG_OUTPUT_ENABLE6, 1, current_val);
>  }
>  
> -static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, u32 value)
> +static u32 ov9282_us_to_flash_duration(struct ov9282 *ov9282, u32 value)
>  {
> -	int ret;
>  	/*
>  	 * Calculate "strobe_frame_span" increments from a given value (µs).
>  	 * This is quite tricky as "The step width of shift and span is
> @@ -703,7 +704,28 @@ static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, u32 value)
>  	 * 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);
> +	u32 frame_width = ov9282->cur_mode->width + ov9282->hblank_ctrl->val;
> +
> +	return value * OV9282_STROBE_SPAN_FACTOR / frame_width;
> +}
> +
> +static u32 ov9282_flash_duration_to_us(struct ov9282 *ov9282, u32 value)
> +{
> +	/*
> +	 * As the calculation in ov9282_us_to_flash_duration uses an integer
> +	 * divison calculate in ns here to get more precision. Then check if
> +	 * we need to compensate that divison by incrementing the µs result.
> +	 */
> +	u32 frame_width = ov9282->cur_mode->width + ov9282->hblank_ctrl->val;
> +	u64 ns = value * 1000 * frame_width / OV9282_STROBE_SPAN_FACTOR;
> +
> +	return DIV_ROUND_UP(ns, 1000);

Can ns even exceed U32_MAX? It doesn't seem to be useful to multiply and
then divide by 1000.

I guess this warrants v9, please fix the other issue for that, too.

> +}
> +
> +static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, u32 value)
> +{
> +	int ret;
> +	u32 val = ov9282_us_to_flash_duration(ov9282, value);
>  
>  	ret = ov9282_write_reg(ov9282, OV9282_REG_STROBE_FRAME_SPAN, 1,
>  			       (val >> 24) & 0xff);
> @@ -798,9 +820,36 @@ static int ov9282_set_ctrl(struct v4l2_ctrl *ctrl)
>  	return ret;
>  }
>  
> +static int ov9282_try_ctrl(struct v4l2_ctrl *ctrl)
> +{
> +	struct ov9282 *ov9282 =
> +		container_of_const(ctrl->handler, struct ov9282, ctrl_handler);
> +
> +	if (ctrl->id == V4L2_CID_FLASH_DURATION) {
> +		u32 us = ctrl->val;
> +		u32 fd = ov9282_us_to_flash_duration(ov9282, us);
> +
> +		/* get nearest strobe_duration value */
> +		u32 us0 = ov9282_flash_duration_to_us(ov9282, fd);
> +		u32 us1 = ov9282_flash_duration_to_us(ov9282, fd + 1);
> +
> +		if (abs(us1 - us) < abs(us - us0))
> +			ctrl->val = us1;
> +		else
> +			ctrl->val = us0;
> +
> +		if (us != ctrl->val)
> +			dev_dbg(ov9282->dev, "using next valid strobe_duration %u instead of %u\n",
> +				ctrl->val, us);
> +	}
> +
> +	return 0;
> +}
> +
>  /* V4l2 subdevice control ops*/
>  static const struct v4l2_ctrl_ops ov9282_ctrl_ops = {
>  	.s_ctrl = ov9282_set_ctrl,
> +	.try_ctrl = ov9282_try_ctrl,
>  };
>  
>  /**
> 

-- 
Regards,

Sakari Ailus