media: ov2740: use group write for digital gain

As the RGB digital gains of ov2740 were not applied as group, some
artifacts were observed in low light environment, use group write for
digital gain can make the RGB digital can be guaranteed to 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+huawei@kernel.org>

drivers/media/i2c/ov2740.c

@@ -51,7 +51,7 @@
 #define OV2740_REG_MWB_R_GAIN		0x500a
 #define OV2740_REG_MWB_G_GAIN		0x500c
 #define OV2740_REG_MWB_B_GAIN		0x500e
-#define OV2740_DGTL_GAIN_MIN		0
+#define OV2740_DGTL_GAIN_MIN		1024
 #define OV2740_DGTL_GAIN_MAX		4095
 #define OV2740_DGTL_GAIN_STEP		1
 #define OV2740_DGTL_GAIN_DEFAULT	1024
@@ -61,6 +61,12 @@
 #define OV2740_TEST_PATTERN_ENABLE	BIT(7)
 #define OV2740_TEST_PATTERN_BAR_SHIFT	2
 
+/* Group Access */
+#define OV2740_REG_GROUP_ACCESS		0x3208
+#define OV2740_GROUP_HOLD_START		0x0
+#define OV2740_GROUP_HOLD_END		0x10
+#define OV2740_GROUP_HOLD_LAUNCH	0xa0
+
 /* ISP CTRL00 */
 #define OV2740_REG_ISP_CTRL00		0x5000
 /* ISP CTRL01 */
@@ -438,6 +444,11 @@ static int ov2740_update_digital_gain(struct ov2740 *ov2740, u32 d_gain)
 {
 	int ret = 0;
 
+	ret = ov2740_write_reg(ov2740, OV2740_REG_GROUP_ACCESS, 1,
+			       OV2740_GROUP_HOLD_START);
+	if (ret)
+		return ret;
+
 	ret = ov2740_write_reg(ov2740, OV2740_REG_MWB_R_GAIN, 2, d_gain);
 	if (ret)
 		return ret;
@@ -446,7 +457,18 @@ static int ov2740_update_digital_gain(struct ov2740 *ov2740, u32 d_gain)
 	if (ret)
 		return ret;
 
-	return ov2740_write_reg(ov2740, OV2740_REG_MWB_B_GAIN, 2, d_gain);
+	ret = ov2740_write_reg(ov2740, OV2740_REG_MWB_B_GAIN, 2, d_gain);
+	if (ret)
+		return ret;
+
+	ret = ov2740_write_reg(ov2740, OV2740_REG_GROUP_ACCESS, 1,
+			       OV2740_GROUP_HOLD_END);
+	if (ret)
+		return ret;
+
+	ret = ov2740_write_reg(ov2740, OV2740_REG_GROUP_ACCESS, 1,
+			       OV2740_GROUP_HOLD_LAUNCH);
+	return ret;
 }
 
 static int ov2740_test_pattern(struct ov2740 *ov2740, u32 pattern)