[PATCH v10 7/8] media: i2c: ov9282: implement try_ctrl for strobe_duration

[Richard Leitner <richard.leitner@linux.dev>]

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 | 55 +++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 52 insertions(+), 3 deletions(-)

diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
index 790d421157e54..4c25b3e11afc0 100644
--- a/drivers/media/i2c/ov9282.c
+++ b/drivers/media/i2c/ov9282.c
@@ -9,6 +9,7 @@
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/i2c.h>
+#include <linux/math.h>
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
 #include <linux/regulator/consumer.h>
@@ -128,6 +129,8 @@
 #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 +694,8 @@ 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 +705,27 @@ 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)
+{
+	/*
+	 * Calculate back to microseconds from "strobe_frame_span" increments.
+	 * As the calculation in ov9282_us_to_flash_duration uses an integer
+	 * divison round up here.
+	 */
+	u32 frame_width = ov9282->cur_mode->width + ov9282->hblank_ctrl->val;
+
+	return DIV_ROUND_UP(value * frame_width, OV9282_STROBE_SPAN_FACTOR);
+}
+
+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);
@@ -807,9 +829,36 @@ 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,
 };
 
 /**

-- 
2.47.3