media: imx290: Add module parameter to automatically switch to HCG mode

The sensor has Low Conversion Gain (HCG) and High Conversion Gain (HCG)
modes, with the supposedly the HCG mode having better noise performance
at high gains.

Based on other devices based on the same sensor, automatically switch
between LCG and HCG at a defined analog gain register threshold.
The threshold can be defined via a module parameter, and defaults to
80, representing 24dB of gain, matching other devices using this module.

Signed-off-by: Dave Stevenson <[email protected]>

drivers/media/i2c/imx290.c

@@ -13,6 +13,7 @@
 #include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/module.h>
+#include <linux/moduleparam.h>
 #include <linux/of.h>
 #include <linux/pm_runtime.h>
 #include <linux/regmap.h>
@@ -41,6 +42,8 @@
 #define IMX290_WINMODE_720P				(1 << 4)
 #define IMX290_WINMODE_CROP				(4 << 4)
 #define IMX290_FR_FDG_SEL				CCI_REG8(0x3009)
+#define IMX290_FDG_HCG					BIT(4)
+#define IMX290_FDG_LCG					0
 #define IMX290_BLKLEVEL					CCI_REG16_LE(0x300a)
 #define IMX290_GAIN					CCI_REG8(0x3014)
 #define IMX290_VMAX					CCI_REG24_LE(0x3018)
@@ -162,6 +165,10 @@
 
 #define IMX290_NUM_SUPPLIES				3
 
+static int hgc_threshold = 80;
+module_param(hgc_threshold, int, 0664);
+MODULE_PARM_DESC(hgc_threshold, "Analog gain threshold to enable HCG mode");
+
 enum imx290_colour_variant {
 	IMX290_VARIANT_COLOUR,
 	IMX290_VARIANT_MONO,
@@ -649,7 +656,6 @@ static int imx290_set_data_lanes(struct imx290 *imx290)
 		  &ret);
 	cci_write(imx290->regmap, IMX290_CSI_LANE_MODE, imx290->nlanes - 1,
 		  &ret);
-	cci_write(imx290->regmap, IMX290_FR_FDG_SEL, 0x01, &ret);
 
 	return ret;
 }
@@ -763,6 +769,10 @@ static int imx290_set_ctrl(struct v4l2_ctrl *ctrl)
 	switch (ctrl->id) {
 	case V4L2_CID_ANALOGUE_GAIN:
 		ret = cci_write(imx290->regmap, IMX290_GAIN, ctrl->val, NULL);
+
+		cci_write(imx290->regmap, IMX290_FR_FDG_SEL,
+			  0x01 | (ctrl->val >= hgc_threshold) ?
+					IMX290_FDG_HCG : IMX290_FDG_LCG, &ret);
 		break;
 
 	case V4L2_CID_VBLANK: