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@linux.dev>
---
 drivers/media/i2c/ov9282.c | 54 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 2 deletions(-)

diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
index 9efc82a1929a76c6fb245e7dbfb5276a133d1c5d..b104ae77f00e9e7777342e48b7bf3caa6d297f69 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_hw_strobe_signal(struct ov9282 *ov9282, bool en
 				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)
 {
 	/*
 	 * Calculate "strobe_frame_span" increments from a given value (µs).
@@ -702,7 +704,27 @@ 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);
+}
+
+static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, u32 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 +814,37 @@ 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;
+
+		/* 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,
 };
 
 /**

-- 
2.47.2

Hi Richard,

kernel test robot noticed the following build errors:

[auto build test ERROR on d9946fe286439c2aeaa7953b8c316efe5b83d515]

url:    https://github.com/intel-lab-lkp/linux/commits/Richard-Leitner/media-v4l-ctrls-add-a-control-for-flash-strobe-duration/20250901-231141
base:   d9946fe286439c2aeaa7953b8c316efe5b83d515
patch link:    https://lore.kernel.org/r/20250901-ov9282-flash-strobe-v7-9-d58d5a694afc%40linux.dev
patch subject: [PATCH v7 09/10] media: i2c: ov9282: implement try_ctrl for strobe_duration
config: sh-randconfig-002-20250905 (https://download.01.org/0day-ci/archive/20250906/202509060108.kK81M3GB-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250906/202509060108.kK81M3GB-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509060108.kK81M3GB-lkp@intel.com/

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: "__udivdi3" [drivers/media/i2c/ov9282.ko] undefined!

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Hi Richard,

On Mon, Sep 01, 2025 at 05:05:14PM +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@linux.dev>
> ---
>  drivers/media/i2c/ov9282.c | 54 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 52 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
> index 9efc82a1929a76c6fb245e7dbfb5276a133d1c5d..b104ae77f00e9e7777342e48b7bf3caa6d297f69 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_hw_strobe_signal(struct ov9282 *ov9282, bool en
>  				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)
>  {
>  	/*
>  	 * Calculate "strobe_frame_span" increments from a given value (µs).
> @@ -702,7 +704,27 @@ 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);
> +}
> +
> +static int ov9282_set_ctrl_flash_duration(struct ov9282 *ov9282, u32 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 +814,37 @@ 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);

container_of_const(), please.

> +
> +	if (ctrl->id == V4L2_CID_FLASH_DURATION) {
> +		u32 fd = ov9282_us_to_flash_duration(ov9282, ctrl->val);
> +		u32 us = ctrl->val;

You could use us as argument to ov9282_us_to_flash_duration() if you switch
the order.

> +
> +		/* get nearest strobe_duration value */
> +		u32 us0 = ov9282_flash_duration_to_us(ov9282, fd);
> +		u32 us1 = ov9282_flash_duration_to_us(ov9282, (fd + 1));

Redundant parentheses.

> +
> +		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);
> +		}

Redundant braces.

> +	}
> +
> +	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,
>  };
>  
>  /**
> 

-- 
Kind regards,

Sakari Ailus