[PATCH 10/21] media: i2c: imx258: Follow normal V4L2 behaviours for clipping exposure

[Dave Stevenson <dave.stevenson@raspberrypi.com>]

V4L2 sensor drivers are expected are expected to clip the supported
exposure range based on the VBLANK configured.
IMX258 wasn't doing that as register 0x350 (FRM_LENGTH_CTL)
switches it to a mode where frame length tracks coarse exposure time.

Disable this mode and clip the range for V4L2_CID_EXPOSURE appropriately
based on V4L2_CID_VBLANK.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
---
 drivers/media/i2c/imx258.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/media/i2c/imx258.c b/drivers/media/i2c/imx258.c
index 433dff7f1fa0..82ffe09e3bdc 100644
--- a/drivers/media/i2c/imx258.c
+++ b/drivers/media/i2c/imx258.c
@@ -37,10 +37,11 @@
 
 /* Exposure control */
 #define IMX258_REG_EXPOSURE		0x0202
+#define IMX258_EXPOSURE_OFFSET		10
 #define IMX258_EXPOSURE_MIN		4
 #define IMX258_EXPOSURE_STEP		1
 #define IMX258_EXPOSURE_DEFAULT		0x640
-#define IMX258_EXPOSURE_MAX		65535
+#define IMX258_EXPOSURE_MAX		(IMX258_VTS_MAX - IMX258_EXPOSURE_OFFSET)
 
 /* Analog gain control */
 #define IMX258_REG_ANALOG_GAIN		0x0204
@@ -366,7 +367,7 @@ static const struct imx258_reg mode_common_regs[] = {
 	{ 0x303A, 0x00 },
 	{ 0x303B, 0x10 },
 	{ 0x300D, 0x00 },
-	{ 0x0350, 0x01 },
+	{ 0x0350, 0x00 },
 	{ 0x0204, 0x00 },
 	{ 0x0205, 0x00 },
 	{ 0x020E, 0x01 },
@@ -739,6 +740,19 @@ static int imx258_update_digital_gain(struct imx258 *imx258, u32 len, u32 val)
 	return 0;
 }
 
+static void imx258_adjust_exposure_range(struct imx258 *imx258)
+{
+	int exposure_max, exposure_def;
+
+	/* Honour the VBLANK limits when setting exposure. */
+	exposure_max = imx258->cur_mode->height + imx258->vblank->val -
+		       IMX258_EXPOSURE_OFFSET;
+	exposure_def = min(exposure_max, imx258->exposure->val);
+	__v4l2_ctrl_modify_range(imx258->exposure, imx258->exposure->minimum,
+				 exposure_max, imx258->exposure->step,
+				 exposure_def);
+}
+
 static int imx258_set_ctrl(struct v4l2_ctrl *ctrl)
 {
 	struct imx258 *imx258 =
@@ -746,6 +760,13 @@ static int imx258_set_ctrl(struct v4l2_ctrl *ctrl)
 	struct i2c_client *client = v4l2_get_subdevdata(&imx258->sd);
 	int ret = 0;
 
+	/*
+	 * The VBLANK control may change the limits of usable exposure, so check
+	 * and adjust if necessary.
+	 */
+	if (ctrl->id == V4L2_CID_VBLANK)
+		imx258_adjust_exposure_range(imx258);
+
 	/*
 	 * Applying V4L2 control value only happens
 	 * when power is up for streaming
-- 
2.25.1