linux-kernel - Re: [PATCH v4 10/10] media: i2c: ov9282: implement try_ctrl for strobe

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Message-ID: <aDTNd7sswLyBNbzd@kekkonen.localdomain>
Date: Mon, 26 May 2025 20:22:15 +0000
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>,
	Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: [PATCH v4 10/10] media: i2c: ov9282: implement try_ctrl for
 strobe_duration

Hi Richard,

Thanks for the update.

On Wed, May 07, 2025 at 09:51:39AM +0200, 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 | 56 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 54 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
> index 09d522d5977ec6fb82028ddb6015f05c9328191d..f75882dcb73bea0e00e2cb37ffc19ec3c3a8b126 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 */
> @@ -691,7 +693,7 @@ static int ov9282_set_ctrl_flash_led_mode(struct ov9282 *ov9282, int mode)
>  				current_val);
>  }
>  
> -static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, int value)
> +static u32 ov9282_us_to_flash_duration(struct ov9282 *ov9282, u32 value)
>  {
>  	/*
>  	 * Calculate "strobe_frame_span" increments from a given value (µs).
> @@ -702,7 +704,31 @@ static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, int 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;
> +	u32 us = ns / 1000;
> +	u32 remainder = ns % 1000;
> +
> +	if (remainder > 0)
> +		us++;

It looks like you're trying to round up here. Wouldn't

	return DIV_ROUND_UP(ns, 1000);

do the same?

> +	return us;
> +}
> +
> +static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, int value)
> +{
> +	u32 val = ov9282_us_to_flash_duration(ov9282, value);
>  
>  	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);
> @@ -792,9 +818,35 @@ 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(ctrl->handler, struct ov9282, ctrl_handler);
> +
> +	if (ctrl->id == V4L2_CID_FLASH_DURATION) {
> +		u32 fd = ov9282_us_to_flash_duration(ov9282, ctrl->val);
> +		u32 us = ctrl->val;
> +		u32 us0 = ov9282_flash_duration_to_us(ov9282, fd);
> +		u32 us1 = ov9282_flash_duration_to_us(ov9282, (fd + 1));
> +
> +		if ((us1 - us) < (us - us0))

Is this missing abs?

> +			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