[PATCH v2 2/8] media: i2c: ov9282: fix pixel rate and line time calculation

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

The OV9282_PIXEL_RATE_8BIT is calculated incorrectly from the
OV9282_LINK_FREQ. The hardware scales the pixel rate by changing the
multiplier from 0x50 (for 10 bit) to 0x60 (for 8 bit). Resulting in a
x1.2 factor.

The current OV9282_PIXEL_RATE_8BIT calculation scales from /10
(for 10 bit) to /8 (for 8 bit). This results in a x1.25 factor.

As all the inputs to the pixel rate calculation are constant in this
driver also define the OV9282_PIXEL_RATE_{8,10}BIT as constants.
Additionally introduce a new function to calculate the current
line time in nanoseconds and use it in ov9282_exposure_to_us().

Kudos to Dave Stevenson for pointing me into the right direction!

Link: https://lore.kernel.org/linux-media/CAPY8ntBaSHjztuSLTOtv9KYvEbmcbinSMJ78ZDg+0sZg-1fz3Q@mail.gmail.com/
Fixes: df60764ea5210 ("media: i2c: ov9282: dynamic flash_duration maximum")
Fixes: 43ac0cac18f41 ("media: i2c: ov9282: Add support for 8bit readout")
Cc: stable@vger.kernel.org
Signed-off-by: Richard Leitner <richard.leitner@linux.dev>
---
 drivers/media/i2c/ov9282.c | 50 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 14 deletions(-)

diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c
index c10b2e205834e..5907f57b34523 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>
@@ -111,11 +113,14 @@
 #define OV9282_LINK_FREQ	400000000
 #define OV9282_NUM_DATA_LANES	2
 
-/* Pixel rate */
-#define OV9282_PIXEL_RATE_10BIT		(OV9282_LINK_FREQ * 2 * \
-					 OV9282_NUM_DATA_LANES / 10)
-#define OV9282_PIXEL_RATE_8BIT		(OV9282_LINK_FREQ * 2 * \
-					 OV9282_NUM_DATA_LANES / 8)
+/*
+ * Pixel rate: Derived from the PLL2 clock tree.
+ * For 10 bit it's exactly the same as the sample PLL configuration.
+ * For 8 bit the PLL2 multiplier (REG_PLL_CTRL_0D) is changed 0x50 -> 0x60,
+ * which results in x1.2 and therefore 160 MHz x 1.2 = 192 MHz.
+ */
+#define OV9282_PIXEL_RATE_10BIT	160000000
+#define OV9282_PIXEL_RATE_8BIT	192000000
 
 /*
  * OV9282 native and active pixel array size.
@@ -472,6 +477,32 @@ 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
+ *
+ * Return: line time in nanoseconds.
+ */
+static u32 ov9282_line_time_ns(struct ov9282 *ov9282)
+{
+	u64 hts = ov9282->cur_mode->width + ov9282->hblank_ctrl->val;
+
+	return div_u64(hts * NSEC_PER_SEC, *ov9282->pixel_rate->p_cur.p_s64);
+}
+
+/**
+ * ov9282_exposure_to_us() - Convert an exposure register value to microseconds
+ * @ov9282: pointer to ov9282 device
+ * @exposure: exposure register value to convert
+ *
+ * Return: microsecond representation 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 +541,6 @@ 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