[PATCH 6/8] media: ov2740: add manual white balance controls

[Maurizio Casciano <mauriziocasciano7@gmail.com>]

The sensor has separate red, green and blue manual white-balance gain
registers, but the driver currently writes the same digital-gain value
to all three channels. This prevents userspace from correcting the
strong color cast of raw Bayer capture.

Expose red- and blue-balance controls relative to the digital gain,
update all three channels under group hold, and always release and
launch the group even when a channel write fails.

Tested on the Yoga Book OV2740 with live gain changes and continuous raw
capture.

Signed-off-by: Maurizio Casciano <mauriziocasciano7@gmail.com>
Assisted-by: Codex:gpt-5.6-sol sparse
---
 drivers/media/i2c/ov2740.c | 71 +++++++++++++++++++++++++++-----------
 1 file changed, 50 insertions(+), 21 deletions(-)

diff --git a/drivers/media/i2c/ov2740.c b/drivers/media/i2c/ov2740.c
index b760d4dc0e68..7651443b28c1 100644
--- a/drivers/media/i2c/ov2740.c
+++ b/drivers/media/i2c/ov2740.c
@@ -607,6 +607,9 @@ struct ov2740 {
 	struct v4l2_ctrl *vblank;
 	struct v4l2_ctrl *hblank;
 	struct v4l2_ctrl *exposure;
+	struct v4l2_ctrl *digital_gain;
+	struct v4l2_ctrl *red_balance;
+	struct v4l2_ctrl *blue_balance;
 
 	/* GPIOs, clocks, regulators */
 	struct gpio_desc *reset_gpio;
@@ -736,35 +739,46 @@ static int ov2740_identify_module(struct ov2740 *ov2740)
 	return 0;
 }
 
-static int ov2740_update_digital_gain(struct ov2740 *ov2740, u32 d_gain)
+static int ov2740_update_mwb_gains(struct ov2740 *ov2740)
 {
-	int ret;
+	u32 green_gain = ov2740->digital_gain->val;
+	u32 red_gain, blue_gain;
+	int end_ret, launch_ret, ret;
+
+	/* Balance controls use 1024 as unity relative to the digital gain. */
+	red_gain = min_t(u64,
+			 DIV_ROUND_CLOSEST_ULL((u64)green_gain *
+					       ov2740->red_balance->val,
+					       OV2740_DGTL_GAIN_DEFAULT),
+			 OV2740_DGTL_GAIN_MAX);
+	blue_gain = min_t(u64,
+			  DIV_ROUND_CLOSEST_ULL((u64)green_gain *
+						ov2740->blue_balance->val,
+						OV2740_DGTL_GAIN_DEFAULT),
+			  OV2740_DGTL_GAIN_MAX);
 
 	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);
+	ret = ov2740_write_reg(ov2740, OV2740_REG_MWB_R_GAIN, 2, red_gain);
 	if (ret)
-		return ret;
+		goto release_group;
 
-	ret = ov2740_write_reg(ov2740, OV2740_REG_MWB_G_GAIN, 2, d_gain);
+	ret = ov2740_write_reg(ov2740, OV2740_REG_MWB_G_GAIN, 2, green_gain);
 	if (ret)
-		return ret;
+		goto release_group;
 
-	ret = ov2740_write_reg(ov2740, OV2740_REG_MWB_B_GAIN, 2, d_gain);
-	if (ret)
-		return ret;
+	ret = ov2740_write_reg(ov2740, OV2740_REG_MWB_B_GAIN, 2, blue_gain);
 
-	ret = ov2740_write_reg(ov2740, OV2740_REG_GROUP_ACCESS, 1,
-			       OV2740_GROUP_HOLD_END);
-	if (ret)
-		return ret;
+release_group:
+	end_ret = ov2740_write_reg(ov2740, OV2740_REG_GROUP_ACCESS, 1,
+				   OV2740_GROUP_HOLD_END);
+	launch_ret = ov2740_write_reg(ov2740, OV2740_REG_GROUP_ACCESS, 1,
+				      OV2740_GROUP_HOLD_LAUNCH);
 
-	ret = ov2740_write_reg(ov2740, OV2740_REG_GROUP_ACCESS, 1,
-			       OV2740_GROUP_HOLD_LAUNCH);
-	return ret;
+	return ret ?: end_ret ?: launch_ret;
 }
 
 static int ov2740_test_pattern(struct ov2740 *ov2740, u32 pattern)
@@ -805,7 +819,9 @@ static int ov2740_set_ctrl(struct v4l2_ctrl *ctrl)
 		break;
 
 	case V4L2_CID_DIGITAL_GAIN:
-		ret = ov2740_update_digital_gain(ov2740, ctrl->val);
+	case V4L2_CID_RED_BALANCE:
+	case V4L2_CID_BLUE_BALANCE:
+		ret = ov2740_update_mwb_gains(ov2740);
 		break;
 
 	case V4L2_CID_EXPOSURE:
@@ -846,7 +862,7 @@ static int ov2740_init_controls(struct ov2740 *ov2740)
 	int ret;
 
 	ctrl_hdlr = &ov2740->ctrl_handler;
-	ret = v4l2_ctrl_handler_init(ctrl_hdlr, 10);
+	ret = v4l2_ctrl_handler_init(ctrl_hdlr, 12);
 	if (ret)
 		return ret;
 
@@ -881,9 +897,22 @@ static int ov2740_init_controls(struct ov2740 *ov2740)
 	v4l2_ctrl_new_std(ctrl_hdlr, &ov2740_ctrl_ops, V4L2_CID_ANALOGUE_GAIN,
 			  OV2740_ANAL_GAIN_MIN, OV2740_ANAL_GAIN_MAX,
 			  OV2740_ANAL_GAIN_STEP, OV2740_ANAL_GAIN_MIN);
-	v4l2_ctrl_new_std(ctrl_hdlr, &ov2740_ctrl_ops, V4L2_CID_DIGITAL_GAIN,
-			  OV2740_DGTL_GAIN_MIN, OV2740_DGTL_GAIN_MAX,
-			  OV2740_DGTL_GAIN_STEP, OV2740_DGTL_GAIN_DEFAULT);
+	ov2740->digital_gain =
+		v4l2_ctrl_new_std(ctrl_hdlr, &ov2740_ctrl_ops,
+				  V4L2_CID_DIGITAL_GAIN,
+				  OV2740_DGTL_GAIN_MIN, OV2740_DGTL_GAIN_MAX,
+				  OV2740_DGTL_GAIN_STEP,
+				  OV2740_DGTL_GAIN_DEFAULT);
+	ov2740->red_balance =
+		v4l2_ctrl_new_std(ctrl_hdlr, &ov2740_ctrl_ops,
+				  V4L2_CID_RED_BALANCE,
+				  1, OV2740_DGTL_GAIN_MAX, 1,
+				  OV2740_DGTL_GAIN_DEFAULT);
+	ov2740->blue_balance =
+		v4l2_ctrl_new_std(ctrl_hdlr, &ov2740_ctrl_ops,
+				  V4L2_CID_BLUE_BALANCE,
+				  1, OV2740_DGTL_GAIN_MAX, 1,
+				  OV2740_DGTL_GAIN_DEFAULT);
 	exposure_max = ov2740->cur_mode->vts_def - OV2740_EXPOSURE_MAX_MARGIN;
 	ov2740->exposure = v4l2_ctrl_new_std(ctrl_hdlr, &ov2740_ctrl_ops,
 					     V4L2_CID_EXPOSURE,
-- 
2.53.0