drivers: media: imx708: Adjust broken line correction parameter

In full-resolution mode, the LPF_INTENSITY_EN and LPF_INTENSITY
registers control Quad Bayer Re-mosaic broken line correction.
Expose this as a module parameter "qbc_adjust": zero disables
the correction and values in the range 2 to 5 set its strength.

There is a trade-off between coloured and monochrome patterns.
The previous fixed value 4 could produce ladder/spots artefacts
in coloured textures. The new default value 2 may suit a wider
range of scenes.

Signed-off-by: Nick Hollinghurst <[email protected]>

drivers/media/i2c/imx708.c

@@ -20,6 +20,14 @@
 #include <media/v4l2-fwnode.h>
 #include <media/v4l2-mediabus.h>
 
+/*
+ * Parameter to adjust Quad Bayer re-mosaic broken line correction
+ * strength, used in full-resolution mode only. Set zero to disable.
+ */
+static int qbc_adjust = 2;
+module_param(qbc_adjust, int, 0644);
+MODULE_PARM_DESC(qbc_adjust, "Quad Bayer broken line correction strength [0,2-5]");
+
 #define IMX708_REG_VALUE_08BIT		1
 #define IMX708_REG_VALUE_16BIT		2
 
@@ -99,11 +107,17 @@
 
 /* HDR exposure ratio (long:med == med:short) */
 #define IMX708_HDR_EXPOSURE_RATIO       4
-#define IMX708_REG_MID_EXPOSURE	0x3116
-#define IMX708_REG_SHT_EXPOSURE	0x0224
+#define IMX708_REG_MID_EXPOSURE		0x3116
+#define IMX708_REG_SHT_EXPOSURE		0x0224
 #define IMX708_REG_MID_ANALOG_GAIN	0x3118
 #define IMX708_REG_SHT_ANALOG_GAIN	0x0216
 
+/* QBC Re-mosaic broken line correction registers */
+#define IMX708_LPF_INTENSITY_EN		0xC428
+#define IMX708_LPF_INTENSITY_ENABLED	0x00
+#define IMX708_LPF_INTENSITY_DISABLED	0x01
+#define IMX708_LPF_INTENSITY		0xC429
+
 /*
  * Metadata buffer holds a variety of data, all sent with the same VC/DT (0x12).
  * It comprises two scanlines (of up to 5760 bytes each, for 4608 pixels)
@@ -171,6 +185,9 @@ struct imx708_mode {
 
 	/* HDR flag, used for checking if the current mode is HDR */
 	bool hdr;
+
+	/* Quad Bayer Re-mosaic flag */
+	bool remosaic;
 };
 
 /* Default PDAF pixel correction gains */
@@ -363,8 +380,6 @@ static const struct imx708_reg mode_4608x2592_regs[] = {
 	{0x341f, 0x20},
 	{0x3420, 0x00},
 	{0x3421, 0xd8},
-	{0xC428, 0x00},
-	{0xC429, 0x04},
 	{0x3366, 0x00},
 	{0x3367, 0x00},
 	{0x3368, 0x00},
@@ -677,7 +692,8 @@ static const struct imx708_mode supported_modes_10bit_no_hdr[] = {
 		.pixel_rate = 595200000,
 		.exposure_lines_min = 8,
 		.exposure_lines_step = 1,
-		.hdr = false
+		.hdr = false,
+		.remosaic = true
 	},
 	{
 		/* regular 2x2 binned. */
@@ -699,7 +715,8 @@ static const struct imx708_mode supported_modes_10bit_no_hdr[] = {
 		.pixel_rate = 585600000,
 		.exposure_lines_min = 4,
 		.exposure_lines_step = 2,
-		.hdr = false
+		.hdr = false,
+		.remosaic = false
 	},
 	{
 		/* 2x2 binned and cropped for 720p. */
@@ -721,7 +738,8 @@ static const struct imx708_mode supported_modes_10bit_no_hdr[] = {
 		.pixel_rate = 566400000,
 		.exposure_lines_min = 4,
 		.exposure_lines_step = 2,
-		.hdr = false
+		.hdr = false,
+		.remosaic = false
 	},
 };
 
@@ -746,7 +764,8 @@ static const struct imx708_mode supported_modes_10bit_hdr[] = {
 		.pixel_rate = 777600000,
 		.exposure_lines_min = 8 * IMX708_HDR_EXPOSURE_RATIO * IMX708_HDR_EXPOSURE_RATIO,
 		.exposure_lines_step = 2 * IMX708_HDR_EXPOSURE_RATIO * IMX708_HDR_EXPOSURE_RATIO,
-		.hdr = true
+		.hdr = true,
+		.remosaic = false
 	}
 };
 
@@ -1515,6 +1534,21 @@ static int imx708_start_streaming(struct imx708 *imx708)
 		return ret;
 	}
 
+	/* Quad Bayer re-mosaic adjustments (for full-resolution mode only) */
+	if (imx708->mode->remosaic && qbc_adjust > 0) {
+		imx708_write_reg(imx708, IMX708_LPF_INTENSITY,
+				 IMX708_REG_VALUE_08BIT, qbc_adjust);
+		imx708_write_reg(imx708,
+				 IMX708_LPF_INTENSITY_EN,
+				 IMX708_REG_VALUE_08BIT,
+				 IMX708_LPF_INTENSITY_ENABLED);
+	} else {
+		imx708_write_reg(imx708,
+				 IMX708_LPF_INTENSITY_EN,
+				 IMX708_REG_VALUE_08BIT,
+				 IMX708_LPF_INTENSITY_DISABLED);
+	}
+
 	/* Apply customized values from user */
 	ret =  __v4l2_ctrl_handler_setup(imx708->sd.ctrl_handler);
 	if (ret)