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

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Message-Id: <20250507-ov9282-flash-strobe-v4-10-72b299c1b7c9@linux.dev>
Date: Wed, 07 May 2025 09:51:39 +0200
From: Richard Leitner <richard.leitner@...ux.dev>
To: 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>, 
 Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org, 
 Richard Leitner <richard.leitner@...ux.dev>
Subject: [PATCH v4 10/10] media: i2c: ov9282: implement try_ctrl for
 strobe_duration

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++;
+	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))
+			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