[PATCH 02/10] media: i2c: ov9282: fix line time and exposure time calculation

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

ov9282_exposure_to_us() divided the line length by the pixel rate control,
which is the MIPI rate and not the clock HTS is counted in. The right
clock is PLL2's system clock. With the PLL2 dividers left at their reset
values the chain

SYS_CLK = XVCLK  / pre_div0 / pre_div * loop_div / sys_pre_div / sys_div
        =    24  /    1     /    3    * loop_div /     4       /    2

collapses to SYS_CLK = loop_div MHz.

Fix this by introducing a new static function to calculate the current
line time and use it in ov9282_exposure_to_us().

Signed-off-by: Richard Leitner <richard.leitner@linux.dev>
---
 drivers/media/i2c/ov9282.c | 46 +++++++++++++++++++++++++++++++++++++---------
 1 file changed, 37 insertions(+), 9 deletions(-)

diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
index c10b2e205834e..3f83a6cf338d8 100644
--- a/drivers/media/i2c/ov9282.c
+++ b/drivers/media/i2c/ov9282.c
@@ -10,10 +10,12 @@
 #include <linux/delay.h>
 #include <linux/i2c.h>
 #include <linux/math.h>
+#include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
 #include <linux/regmap.h>
 #include <linux/regulator/consumer.h>
+#include <linux/time64.h>
 
 #include <media/v4l2-cci.h>
 #include <media/v4l2-ctrls.h>
@@ -472,6 +474,41 @@ static inline struct ov9282 *to_ov9282(struct v4l2_subdev *subdev)
 	return container_of(subdev, struct ov9282, sd);
 }
 
+/**
+ * ov9282_line_time_ns() - Calculate duration of one sensor line.
+ * @ov9282: pointer to ov9282 device
+ *
+ * The line time and therefore OV9282_REG_TIMING_HTS and the strobe frame span
+ * are counted in PLL2's system clock. We assume the PLL2 dividers are at their
+ * reset values, so the formula reduces to SYS_CLK = loop_div MHz.
+ *
+ * Return: line time in nanoseconds.
+ */
+static u32 ov9282_line_time_ns(struct ov9282 *ov9282)
+{
+	u32 hts = ov9282->cur_mode->width + ov9282->hblank_ctrl->val;
+	u32 sclk_rate_mhz = ov9282->code == MEDIA_BUS_FMT_Y10_1X10 ?
+		OV9282_PLL_CTRL_0D_RAW10 : OV9282_PLL_CTRL_0D_RAW8;
+
+	/*
+	 * OV9282_REG_TIMING_HTS counts 2-pixel units
+	 */
+	return DIV_ROUND_CLOSEST(hts * (u32)NSEC_PER_USEC, 2 * sclk_rate_mhz);
+}
+
+/**
+ * ov9282_exposure_to_us() - Convert an exposure register value to microseconds
+ * @ov9282: pointer to ov9282 device
+ * @exposure: exposure register value to convert
+ *
+ * Return: microsecond represenation of the given exposure register value.
+ */
+static u32 ov9282_exposure_to_us(struct ov9282 *ov9282, u32 exposure)
+{
+	return div_u64((u64)exposure * ov9282_line_time_ns(ov9282),
+		       NSEC_PER_USEC);
+}
+
 /**
  * ov9282_update_controls() - Update control ranges based on streaming mode
  * @ov9282: pointer to ov9282 device
@@ -510,15 +547,6 @@ static int ov9282_update_controls(struct ov9282 *ov9282,
 					mode->vblank_max, 1, mode->vblank);
 }
 
-static u32 ov9282_exposure_to_us(struct ov9282 *ov9282, u32 exposure)
-{
-	/* calculate exposure time in µs */
-	u32 frame_width = ov9282->cur_mode->width + ov9282->hblank_ctrl->val;
-	u32 trow_us = frame_width / (ov9282->pixel_rate->val / 1000000UL);
-
-	return exposure * trow_us;
-}
-
 /**
  * ov9282_update_exp_gain() - Set updated exposure and gain
  * @ov9282: pointer to ov9282 device

-- 
2.53.0