media: imx258: add vblank control to support wide frame rate range

Current imx258 driver enable the automatic frame length tracking control
by default and did not support VBLANK change, it's always working at 30fps.
However, in reality we need a wider frame rate range from 15 to 30.
This patch disable the automatic frame length tracking control and enable
the v4l2 VBLANK control to allow user changing frame rate per requirement.

Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>

drivers/media/i2c/imx258.c

@@ -29,6 +29,7 @@
 #define IMX258_VTS_MAX			0xffff
 
 /*Frame Length Line*/
+#define IMX258_REG_FLL			0x0340
 #define IMX258_FLL_MIN			0x08a6
 #define IMX258_FLL_MAX			0xffff
 #define IMX258_FLL_STEP			1
@@ -241,7 +242,7 @@ static const struct imx258_reg mode_4208x3118_regs[] = {
 	{ 0x034D, 0x70 },
 	{ 0x034E, 0x0C },
 	{ 0x034F, 0x30 },
-	{ 0x0350, 0x01 },
+	{ 0x0350, 0x00 },
 	{ 0x0202, 0x0C },
 	{ 0x0203, 0x46 },
 	{ 0x0204, 0x00 },
@@ -360,7 +361,7 @@ static const struct imx258_reg mode_2104_1560_regs[] = {
 	{ 0x034D, 0x38 },
 	{ 0x034E, 0x06 },
 	{ 0x034F, 0x18 },
-	{ 0x0350, 0x01 },
+	{ 0x0350, 0x00 },
 	{ 0x0202, 0x06 },
 	{ 0x0203, 0x2E },
 	{ 0x0204, 0x00 },
@@ -479,7 +480,7 @@ static const struct imx258_reg mode_1048_780_regs[] = {
 	{ 0x034D, 0x18 },
 	{ 0x034E, 0x03 },
 	{ 0x034F, 0x0C },
-	{ 0x0350, 0x01 },
+	{ 0x0350, 0x00 },
 	{ 0x0202, 0x03 },
 	{ 0x0203, 0x42 },
 	{ 0x0204, 0x00 },
@@ -753,8 +754,18 @@ static int imx258_set_ctrl(struct v4l2_ctrl *ctrl)
 	struct imx258 *imx258 =
 		container_of(ctrl->handler, struct imx258, ctrl_handler);
 	struct i2c_client *client = v4l2_get_subdevdata(&imx258->sd);
+	s64 max;
 	int ret = 0;
 
+	if (ctrl->id == V4L2_CID_VBLANK) {
+		/* Update max exposure to meet expected vblanking */
+		max = imx258->cur_mode->height + ctrl->val - 10;
+		__v4l2_ctrl_modify_range(imx258->exposure,
+					 imx258->exposure->minimum,
+					 max, imx258->exposure->step, max);
+		break;
+	}
+
 	/*
 	 * Applying V4L2 control value only happens
 	 * when power is up for streaming
@@ -773,6 +784,10 @@ static int imx258_set_ctrl(struct v4l2_ctrl *ctrl)
 				IMX258_REG_VALUE_16BIT,
 				ctrl->val);
 		break;
+	case V4L2_CID_VBLANK:
+		ret = imx258_write_reg(imx258, IMX258_REG_FLL, 2,
+				       imx258->cur_mode->height + ctrl->val);
+		break;
 	case V4L2_CID_DIGITAL_GAIN:
 		ret = imx258_update_digital_gain(imx258, IMX258_REG_VALUE_16BIT,
 				ctrl->val);
@@ -1189,9 +1204,6 @@ static int imx258_init_controls(struct imx258 *imx258)
 				IMX258_VTS_MAX - imx258->cur_mode->height, 1,
 				vblank_def);
 
-	if (imx258->vblank)
-		imx258->vblank->flags |= V4L2_CTRL_FLAG_READ_ONLY;
-
 	imx258->hblank = v4l2_ctrl_new_std(
 				ctrl_hdlr, &imx258_ctrl_ops, V4L2_CID_HBLANK,
 				IMX258_PPL_DEFAULT - imx258->cur_mode->width,