media: i2c: imx219: make HBLANK r/w to allow longer exposures

The HBLANK control was read-only, and always configured such
that the sensor HTS register was 3448. This limited the maximum
exposure time that could be achieved to around 1.26 secs.

Make HBLANK read/write so that the line time can be extended,
and thereby allow longer exposures (and slower frame rates).
Retain the overall HTS setting when changing modes rather than
resetting it to a default.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

drivers/media/i2c/imx219.c

@@ -63,8 +63,10 @@
 #define IMX219_FLL_STEP			1
 #define IMX219_FLL_DEFAULT		0x0c98
 
-/* HBLANK control - read only */
-#define IMX219_PPL_DEFAULT		3448
+/* HBLANK control range */
+#define IMX219_PPL_MIN			3448
+#define IMX219_PPL_MAX			0x7ff0
+#define IMX219_REG_HTS			0x0162
 
 /* Exposure control */
 #define IMX219_REG_EXPOSURE		0x015a
@@ -191,8 +193,6 @@ static const struct imx219_reg imx219_common_regs[] = {
 	{0x479b, 0x0e},
 
 	/* Frame Bank Register Group "A" */
-	{0x0162, 0x0d},	/* Line_Length_A */
-	{0x0163, 0x78},
 	{0x0170, 0x01}, /* X_ODD_INC_A */
 	{0x0171, 0x01}, /* Y_ODD_INC_A */
 
@@ -679,6 +679,11 @@ static int imx219_set_ctrl(struct v4l2_ctrl *ctrl)
 				       IMX219_REG_VALUE_16BIT,
 				       imx219->mode->height + ctrl->val);
 		break;
+	case V4L2_CID_HBLANK:
+		ret = imx219_write_reg(imx219, IMX219_REG_HTS,
+				       IMX219_REG_VALUE_16BIT,
+				       imx219->mode->width + ctrl->val);
+		break;
 	case V4L2_CID_TEST_PATTERN_RED:
 		ret = imx219_write_reg(imx219, IMX219_REG_TESTP_RED,
 				       IMX219_REG_VALUE_16BIT, ctrl->val);
@@ -837,6 +842,8 @@ static int imx219_set_pad_format(struct v4l2_subdev *sd,
 		*framefmt = fmt->format;
 	} else if (imx219->mode != mode ||
 		   imx219->fmt.code != fmt->format.code) {
+		u32 prev_hts = imx219->mode->width + imx219->hblank->val;
+
 		imx219->fmt = fmt->format;
 		imx219->mode = mode;
 		/* Update limits and set FPS to default */
@@ -854,13 +861,19 @@ static int imx219_set_pad_format(struct v4l2_subdev *sd,
 					 exposure_max, imx219->exposure->step,
 					 exposure_def);
 		/*
-		 * Currently PPL is fixed to IMX219_PPL_DEFAULT, so hblank
-		 * depends on mode->width only, and is not changeble in any
-		 * way other than changing the mode.
+		 * Retain PPL setting from previous mode so that the
+		 * line time does not change on a mode change.
+		 * Limits have to be recomputed as the controls define
+		 * the blanking only, so PPL values need to have the
+		 * mode width subtracted.
 		 */
-		hblank = IMX219_PPL_DEFAULT - mode->width;
-		__v4l2_ctrl_modify_range(imx219->hblank, hblank, hblank, 1,
-					 hblank);
+		hblank = prev_hts - mode->width;
+		__v4l2_ctrl_modify_range(imx219->hblank,
+					 IMX219_PPL_MIN - mode->width,
+					 IMX219_PPL_MAX - mode->width,
+					 1,
+					 IMX219_PPL_MIN - mode->width);
+		__v4l2_ctrl_s_ctrl(imx219->hblank, hblank);
 	}
 
 	mutex_unlock(&imx219->mutex);
@@ -1263,12 +1276,10 @@ static int imx219_init_controls(struct imx219 *imx219)
 					   V4L2_CID_VBLANK, IMX219_VBLANK_MIN,
 					   IMX219_VTS_MAX - height, 1,
 					   imx219->mode->vts_def - height);
-	hblank = IMX219_PPL_DEFAULT - imx219->mode->width;
+	hblank = IMX219_PPL_MIN - imx219->mode->width;
 	imx219->hblank = v4l2_ctrl_new_std(ctrl_hdlr, &imx219_ctrl_ops,
 					   V4L2_CID_HBLANK, hblank, hblank,
 					   1, hblank);
-	if (imx219->hblank)
-		imx219->hblank->flags |= V4L2_CTRL_FLAG_READ_ONLY;
 	exposure_max = imx219->mode->vts_def - 4;
 	exposure_def = (exposure_max < IMX219_EXPOSURE_DEFAULT) ?
 		exposure_max : IMX219_EXPOSURE_DEFAULT;