media: ov5675: use group write to update digital gain

MWB gain register are used to set gain for each mwb channel mannually.
However, it will involve some artifacts at low light environment as gain
cannot be applied to each channel synchronously. Update the driver to use
group write for digital gain to make the sure RGB digital gain be applied
together at frame boundary.
Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/i2c/ov5675.c

@@ -50,14 +50,21 @@
 #define	OV5675_ANAL_GAIN_STEP		1
 
 /* Digital gain controls from sensor */
+#define OV5675_REG_DIGITAL_GAIN		0x350a
 #define OV5675_REG_MWB_R_GAIN		0x5019
 #define OV5675_REG_MWB_G_GAIN		0x501b
 #define OV5675_REG_MWB_B_GAIN		0x501d
-#define OV5675_DGTL_GAIN_MIN		0
+#define OV5675_DGTL_GAIN_MIN		1024
 #define OV5675_DGTL_GAIN_MAX		4095
 #define OV5675_DGTL_GAIN_STEP		1
 #define OV5675_DGTL_GAIN_DEFAULT	1024
 
+/* Group Access */
+#define OV5675_REG_GROUP_ACCESS		0x3208
+#define OV5675_GROUP_HOLD_START		0x0
+#define OV5675_GROUP_HOLD_END		0x10
+#define OV5675_GROUP_HOLD_LAUNCH	0xa0
+
 /* Test Pattern Control */
 #define OV5675_REG_TEST_PATTERN		0x4503
 #define OV5675_TEST_PATTERN_ENABLE	BIT(7)
@@ -587,6 +594,12 @@ static int ov5675_update_digital_gain(struct ov5675 *ov5675, u32 d_gain)
 {
 	int ret;
 
+	ret = ov5675_write_reg(ov5675, OV5675_REG_GROUP_ACCESS,
+			       OV5675_REG_VALUE_08BIT,
+			       OV5675_GROUP_HOLD_START);
+	if (ret)
+		return ret;
+
 	ret = ov5675_write_reg(ov5675, OV5675_REG_MWB_R_GAIN,
 			       OV5675_REG_VALUE_16BIT, d_gain);
 	if (ret)
@@ -597,8 +610,21 @@ static int ov5675_update_digital_gain(struct ov5675 *ov5675, u32 d_gain)
 	if (ret)
 		return ret;
 
-	return ov5675_write_reg(ov5675, OV5675_REG_MWB_B_GAIN,
+	ret = ov5675_write_reg(ov5675, OV5675_REG_MWB_B_GAIN,
 			       OV5675_REG_VALUE_16BIT, d_gain);
+	if (ret)
+		return ret;
+
+	ret = ov5675_write_reg(ov5675, OV5675_REG_GROUP_ACCESS,
+			       OV5675_REG_VALUE_08BIT,
+			       OV5675_GROUP_HOLD_END);
+	if (ret)
+		return ret;
+
+	ret = ov5675_write_reg(ov5675, OV5675_REG_GROUP_ACCESS,
+			       OV5675_REG_VALUE_08BIT,
+			       OV5675_GROUP_HOLD_LAUNCH);
+	return ret;
 }
 
 static int ov5675_test_pattern(struct ov5675 *ov5675, u32 pattern)