diff mbox series

[v2,08/13] media: i2c: imx214: Add vblank and hblank controls

Message ID 20241021-imx214-v2-8-fbd23e99541e@apitzsch.eu (mailing list archive)
State New
Headers show
Series media: i2c: imx214: Miscellaneous cleanups and improvements | expand

Commit Message

André Apitzsch via B4 Relay Oct. 20, 2024, 10:13 p.m. UTC
From: André Apitzsch <git@apitzsch.eu>

Add vblank control to allow changing the framerate /
higher exposure values.

The vblank and hblank controls are needed for libcamera support.

While at it, fix the minimal exposure time according to the datasheet.

Signed-off-by: André Apitzsch <git@apitzsch.eu>
---
 drivers/media/i2c/imx214.c | 119 ++++++++++++++++++++++++++++++++++++---------
 1 file changed, 97 insertions(+), 22 deletions(-)

Comments

Ricardo Ribalda Delgado Oct. 30, 2024, 11:57 a.m. UTC | #1
On Mon, Oct 21, 2024 at 12:14 AM André Apitzsch via B4 Relay
<devnull+git.apitzsch.eu@kernel.org> wrote:
>
> From: André Apitzsch <git@apitzsch.eu>
>
> Add vblank control to allow changing the framerate /
> higher exposure values.
>
> The vblank and hblank controls are needed for libcamera support.
>
> While at it, fix the minimal exposure time according to the datasheet.
>
> Signed-off-by: André Apitzsch <git@apitzsch.eu>
> ---
>  drivers/media/i2c/imx214.c | 119 ++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 97 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/media/i2c/imx214.c b/drivers/media/i2c/imx214.c
> index 497baad616ad7374a92a3da2b7c1096b1d72a0c7..cb443d8bee6fe72dc9378b2c2d3caae09f8642c5 100644
> --- a/drivers/media/i2c/imx214.c
> +++ b/drivers/media/i2c/imx214.c
> @@ -34,11 +34,18 @@
>
>  /* V-TIMING internal */
>  #define IMX214_REG_FRM_LENGTH_LINES    CCI_REG16(0x0340)
> +#define IMX214_VTS_MAX                 0xffff
> +
> +#define IMX214_VBLANK_MIN              890
> +
> +/* HBLANK control - read only */
> +#define IMX214_PPL_DEFAULT             5008
>
>  /* Exposure control */
>  #define IMX214_REG_EXPOSURE            CCI_REG16(0x0202)
> -#define IMX214_EXPOSURE_MIN            0
> -#define IMX214_EXPOSURE_MAX            3184
> +#define IMX214_EXPOSURE_OFFSET         10
> +#define IMX214_EXPOSURE_MIN            1
> +#define IMX214_EXPOSURE_MAX            (IMX214_VTS_MAX - IMX214_EXPOSURE_OFFSET)
this definition is never used
>  #define IMX214_EXPOSURE_STEP           1
>  #define IMX214_EXPOSURE_DEFAULT                3184
>  #define IMX214_REG_EXPOSURE_RATIO      CCI_REG8(0x0222)
> @@ -187,6 +194,8 @@ struct imx214 {
>         struct v4l2_ctrl_handler ctrls;
>         struct v4l2_ctrl *pixel_rate;
>         struct v4l2_ctrl *link_freq;
> +       struct v4l2_ctrl *vblank;
> +       struct v4l2_ctrl *hblank;
>         struct v4l2_ctrl *exposure;
>         struct v4l2_ctrl *unit_size;
>
> @@ -202,8 +211,6 @@ static const struct cci_reg_sequence mode_4096x2304[] = {
>         { IMX214_REG_HDR_MODE, IMX214_HDR_MODE_OFF },
>         { IMX214_REG_HDR_RES_REDUCTION, IMX214_HDR_RES_REDU_THROUGH },
>         { IMX214_REG_EXPOSURE_RATIO, 1 },
> -       { IMX214_REG_FRM_LENGTH_LINES, 3194 },
> -       { IMX214_REG_LINE_LENGTH_PCK, 5008 },
>         { IMX214_REG_X_ADD_STA, 56 },
>         { IMX214_REG_Y_ADD_STA, 408 },
>         { IMX214_REG_X_ADD_END, 4151 },
> @@ -274,8 +281,6 @@ static const struct cci_reg_sequence mode_1920x1080[] = {
>         { IMX214_REG_HDR_MODE, IMX214_HDR_MODE_OFF },
>         { IMX214_REG_HDR_RES_REDUCTION, IMX214_HDR_RES_REDU_THROUGH },
>         { IMX214_REG_EXPOSURE_RATIO, 1 },
> -       { IMX214_REG_FRM_LENGTH_LINES, 3194 },
> -       { IMX214_REG_LINE_LENGTH_PCK, 5008 },
>         { IMX214_REG_X_ADD_STA, 1144 },
>         { IMX214_REG_Y_ADD_STA, 1020 },
>         { IMX214_REG_X_ADD_END, 3063 },
> @@ -359,6 +364,7 @@ static const struct cci_reg_sequence mode_table_common[] = {
>         { IMX214_REG_ORIENTATION, 0 },
>         { IMX214_REG_MASK_CORR_FRAMES, IMX214_CORR_FRAMES_MASK },
>         { IMX214_REG_FAST_STANDBY_CTRL, 1 },
> +       { IMX214_REG_LINE_LENGTH_PCK, IMX214_PPL_DEFAULT },
>         { CCI_REG8(0x4550), 0x02 },
>         { CCI_REG8(0x4601), 0x00 },
>         { CCI_REG8(0x4642), 0x05 },
> @@ -462,18 +468,24 @@ static const struct cci_reg_sequence mode_table_common[] = {
>  static const struct imx214_mode {
>         u32 width;
>         u32 height;
> +
> +       /* V-timing */
> +       unsigned int vts_def;
> +
>         unsigned int num_of_regs;
>         const struct cci_reg_sequence *reg_table;
>  } imx214_modes[] = {
>         {
>                 .width = 4096,
>                 .height = 2304,
> +               .vts_def = 3194,
>                 .num_of_regs = ARRAY_SIZE(mode_4096x2304),
>                 .reg_table = mode_4096x2304,
>         },
>         {
>                 .width = 1920,
>                 .height = 1080,
> +               .vts_def = 3194,
>                 .num_of_regs = ARRAY_SIZE(mode_1920x1080),
>                 .reg_table = mode_1920x1080,
>         },
> @@ -629,9 +641,39 @@ static int imx214_set_format(struct v4l2_subdev *sd,
>         __crop->width = mode->width;
>         __crop->height = mode->height;
>
> -       if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE)
> +       if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE) {
> +               int exposure_max;
> +               int exposure_def;
> +               int hblank;
> +
>                 imx214->cur_mode = mode;
>
> +               /* Update limits and set FPS to default */
> +               __v4l2_ctrl_modify_range(imx214->vblank, IMX214_VBLANK_MIN,
> +                                        IMX214_VTS_MAX - mode->height, 2,
> +                                        mode->vts_def - mode->height);
> +               __v4l2_ctrl_s_ctrl(imx214->vblank,
> +                                  mode->vts_def - mode->height);

Do we need to set FPS to default?

> +
> +               /* Update max exposure while meeting expected vblanking */
> +               exposure_max = mode->vts_def - IMX214_EXPOSURE_OFFSET;
> +               exposure_def = (exposure_max < IMX214_EXPOSURE_DEFAULT) ?
> +                       exposure_max : IMX214_EXPOSURE_DEFAULT;
exposure_def = min(exposure_max, IMX214_EXPOSURE_DEFAULT);
> +               __v4l2_ctrl_modify_range(imx214->exposure,
> +                                        imx214->exposure->minimum,
> +                                        exposure_max, imx214->exposure->step,
> +                                        exposure_def);
> +
> +               /*
> +                * Currently PPL is fixed to IMX214_PPL_DEFAULT, so hblank
> +                * depends on mode->width only, and is not changeble in any
> +                * way other than changing the mode.
> +                */
> +               hblank = IMX214_PPL_DEFAULT - mode->width;
> +               __v4l2_ctrl_modify_range(imx214->hblank, hblank, hblank, 1,
> +                                        hblank);
> +       }
> +
>         return 0;
>  }
>
> @@ -681,8 +723,25 @@ static int imx214_set_ctrl(struct v4l2_ctrl *ctrl)
>  {
>         struct imx214 *imx214 = container_of(ctrl->handler,
>                                              struct imx214, ctrls);
> +       const struct v4l2_mbus_framefmt *format;
> +       struct v4l2_subdev_state *state;
>         int ret;
>
> +       state = v4l2_subdev_get_locked_active_state(&imx214->sd);
> +       format = v4l2_subdev_state_get_format(state, 0);
> +
> +       if (ctrl->id == V4L2_CID_VBLANK) {
> +               int exposure_max, exposure_def;
Not sure if the compiler will like it, but have you tried to set state
and format under this if?

> +
> +               /* Update max exposure while meeting expected vblanking */
> +               exposure_max = format->height + ctrl->val - IMX214_EXPOSURE_OFFSET;
> +               exposure_def = min(exposure_max, IMX214_EXPOSURE_DEFAULT);
> +               __v4l2_ctrl_modify_range(imx214->exposure,
> +                                        imx214->exposure->minimum,
> +                                        exposure_max, imx214->exposure->step,
> +                                        exposure_def);
> +       }
> +
>         /*
>          * Applying V4L2 control value only happens
>          * when power is up for streaming
> @@ -694,7 +753,10 @@ static int imx214_set_ctrl(struct v4l2_ctrl *ctrl)
>         case V4L2_CID_EXPOSURE:
>                 cci_write(imx214->regmap, IMX214_REG_EXPOSURE, ctrl->val, &ret);
>                 break;
> -
> +       case V4L2_CID_VBLANK:
> +               cci_write(imx214->regmap, IMX214_REG_FRM_LENGTH_LINES,
> +                         format->height + ctrl->val, &ret);
> +               break;
>         default:
>                 ret = -EINVAL;
>         }
> @@ -717,8 +779,11 @@ static int imx214_ctrls_init(struct imx214 *imx214)
>                 .width = 1120,
>                 .height = 1120,
>         };
> +       const struct imx214_mode *mode = &imx214_modes[0];
>         struct v4l2_fwnode_device_properties props;
>         struct v4l2_ctrl_handler *ctrl_hdlr;
> +       int exposure_max, exposure_def;
> +       int hblank;
>         int ret;
>
>         ret = v4l2_fwnode_device_parse(imx214->dev, &props);
> @@ -726,7 +791,7 @@ static int imx214_ctrls_init(struct imx214 *imx214)
>                 return ret;
>
>         ctrl_hdlr = &imx214->ctrls;
> -       ret = v4l2_ctrl_handler_init(&imx214->ctrls, 6);
> +       ret = v4l2_ctrl_handler_init(&imx214->ctrls, 8);
>         if (ret)
>                 return ret;
>
> @@ -742,22 +807,26 @@ static int imx214_ctrls_init(struct imx214 *imx214)
>         if (imx214->link_freq)
>                 imx214->link_freq->flags |= V4L2_CTRL_FLAG_READ_ONLY;
>
> -       /*
> -        * WARNING!
> -        * Values obtained reverse engineering blobs and/or devices.
> -        * Ranges and functionality might be wrong.
> -        *
> -        * Sony, please release some register set documentation for the
> -        * device.
> -        *
> -        * Yours sincerely, Ricardo.
> -        */
Please keep my message ;)


> +       /* Initial vblank/hblank/exposure parameters based on current mode */
> +       imx214->vblank = v4l2_ctrl_new_std(ctrl_hdlr, &imx214_ctrl_ops,
> +                                          V4L2_CID_VBLANK, IMX214_VBLANK_MIN,
> +                                          IMX214_VTS_MAX - mode->height, 2,
> +                                          mode->vts_def - mode->height);
> +
> +       hblank = IMX214_PPL_DEFAULT - mode->width;
> +       imx214->hblank = v4l2_ctrl_new_std(ctrl_hdlr, &imx214_ctrl_ops,
> +                                          V4L2_CID_HBLANK, hblank, hblank,
> +                                          1, hblank);
> +       if (imx214->hblank)
> +               imx214->hblank->flags |= V4L2_CTRL_FLAG_READ_ONLY;
> +
> +       exposure_max = mode->vts_def - IMX214_EXPOSURE_OFFSET;
> +       exposure_def = min(exposure_max, IMX214_EXPOSURE_DEFAULT);
>         imx214->exposure = v4l2_ctrl_new_std(ctrl_hdlr, &imx214_ctrl_ops,
>                                              V4L2_CID_EXPOSURE,
> -                                            IMX214_EXPOSURE_MIN,
> -                                            IMX214_EXPOSURE_MAX,
> +                                            IMX214_EXPOSURE_MIN, exposure_max,
>                                              IMX214_EXPOSURE_STEP,
> -                                            IMX214_EXPOSURE_DEFAULT);
> +                                            exposure_def);
>
>         imx214->unit_size = v4l2_ctrl_new_std_compound(ctrl_hdlr,
>                                 NULL,
> @@ -879,6 +948,12 @@ static int imx214_get_frame_interval(struct v4l2_subdev *subdev,
>         return 0;
>  }
>
> +/*
> + * Raw sensors should be using the VBLANK and HBLANK controls to determine
> + * the frame rate. However this driver was initially added using the
> + * [S|G|ENUM]_FRAME_INTERVAL ioctls with a fixed rate of 30fps.
> + * Retain the frame_interval ops for backwards compatibility, but they do nothing.
> + */
>  static int imx214_enum_frame_interval(struct v4l2_subdev *subdev,
>                                 struct v4l2_subdev_state *sd_state,
>                                 struct v4l2_subdev_frame_interval_enum *fie)
>
> --
> 2.47.0
>
>
diff mbox series

Patch

diff --git a/drivers/media/i2c/imx214.c b/drivers/media/i2c/imx214.c
index 497baad616ad7374a92a3da2b7c1096b1d72a0c7..cb443d8bee6fe72dc9378b2c2d3caae09f8642c5 100644
--- a/drivers/media/i2c/imx214.c
+++ b/drivers/media/i2c/imx214.c
@@ -34,11 +34,18 @@ 
 
 /* V-TIMING internal */
 #define IMX214_REG_FRM_LENGTH_LINES	CCI_REG16(0x0340)
+#define IMX214_VTS_MAX			0xffff
+
+#define IMX214_VBLANK_MIN		890
+
+/* HBLANK control - read only */
+#define IMX214_PPL_DEFAULT		5008
 
 /* Exposure control */
 #define IMX214_REG_EXPOSURE		CCI_REG16(0x0202)
-#define IMX214_EXPOSURE_MIN		0
-#define IMX214_EXPOSURE_MAX		3184
+#define IMX214_EXPOSURE_OFFSET		10
+#define IMX214_EXPOSURE_MIN		1
+#define IMX214_EXPOSURE_MAX		(IMX214_VTS_MAX - IMX214_EXPOSURE_OFFSET)
 #define IMX214_EXPOSURE_STEP		1
 #define IMX214_EXPOSURE_DEFAULT		3184
 #define IMX214_REG_EXPOSURE_RATIO	CCI_REG8(0x0222)
@@ -187,6 +194,8 @@  struct imx214 {
 	struct v4l2_ctrl_handler ctrls;
 	struct v4l2_ctrl *pixel_rate;
 	struct v4l2_ctrl *link_freq;
+	struct v4l2_ctrl *vblank;
+	struct v4l2_ctrl *hblank;
 	struct v4l2_ctrl *exposure;
 	struct v4l2_ctrl *unit_size;
 
@@ -202,8 +211,6 @@  static const struct cci_reg_sequence mode_4096x2304[] = {
 	{ IMX214_REG_HDR_MODE, IMX214_HDR_MODE_OFF },
 	{ IMX214_REG_HDR_RES_REDUCTION, IMX214_HDR_RES_REDU_THROUGH },
 	{ IMX214_REG_EXPOSURE_RATIO, 1 },
-	{ IMX214_REG_FRM_LENGTH_LINES, 3194 },
-	{ IMX214_REG_LINE_LENGTH_PCK, 5008 },
 	{ IMX214_REG_X_ADD_STA, 56 },
 	{ IMX214_REG_Y_ADD_STA, 408 },
 	{ IMX214_REG_X_ADD_END, 4151 },
@@ -274,8 +281,6 @@  static const struct cci_reg_sequence mode_1920x1080[] = {
 	{ IMX214_REG_HDR_MODE, IMX214_HDR_MODE_OFF },
 	{ IMX214_REG_HDR_RES_REDUCTION, IMX214_HDR_RES_REDU_THROUGH },
 	{ IMX214_REG_EXPOSURE_RATIO, 1 },
-	{ IMX214_REG_FRM_LENGTH_LINES, 3194 },
-	{ IMX214_REG_LINE_LENGTH_PCK, 5008 },
 	{ IMX214_REG_X_ADD_STA, 1144 },
 	{ IMX214_REG_Y_ADD_STA, 1020 },
 	{ IMX214_REG_X_ADD_END, 3063 },
@@ -359,6 +364,7 @@  static const struct cci_reg_sequence mode_table_common[] = {
 	{ IMX214_REG_ORIENTATION, 0 },
 	{ IMX214_REG_MASK_CORR_FRAMES, IMX214_CORR_FRAMES_MASK },
 	{ IMX214_REG_FAST_STANDBY_CTRL, 1 },
+	{ IMX214_REG_LINE_LENGTH_PCK, IMX214_PPL_DEFAULT },
 	{ CCI_REG8(0x4550), 0x02 },
 	{ CCI_REG8(0x4601), 0x00 },
 	{ CCI_REG8(0x4642), 0x05 },
@@ -462,18 +468,24 @@  static const struct cci_reg_sequence mode_table_common[] = {
 static const struct imx214_mode {
 	u32 width;
 	u32 height;
+
+	/* V-timing */
+	unsigned int vts_def;
+
 	unsigned int num_of_regs;
 	const struct cci_reg_sequence *reg_table;
 } imx214_modes[] = {
 	{
 		.width = 4096,
 		.height = 2304,
+		.vts_def = 3194,
 		.num_of_regs = ARRAY_SIZE(mode_4096x2304),
 		.reg_table = mode_4096x2304,
 	},
 	{
 		.width = 1920,
 		.height = 1080,
+		.vts_def = 3194,
 		.num_of_regs = ARRAY_SIZE(mode_1920x1080),
 		.reg_table = mode_1920x1080,
 	},
@@ -629,9 +641,39 @@  static int imx214_set_format(struct v4l2_subdev *sd,
 	__crop->width = mode->width;
 	__crop->height = mode->height;
 
-	if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE)
+	if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE) {
+		int exposure_max;
+		int exposure_def;
+		int hblank;
+
 		imx214->cur_mode = mode;
 
+		/* Update limits and set FPS to default */
+		__v4l2_ctrl_modify_range(imx214->vblank, IMX214_VBLANK_MIN,
+					 IMX214_VTS_MAX - mode->height, 2,
+					 mode->vts_def - mode->height);
+		__v4l2_ctrl_s_ctrl(imx214->vblank,
+				   mode->vts_def - mode->height);
+
+		/* Update max exposure while meeting expected vblanking */
+		exposure_max = mode->vts_def - IMX214_EXPOSURE_OFFSET;
+		exposure_def = (exposure_max < IMX214_EXPOSURE_DEFAULT) ?
+			exposure_max : IMX214_EXPOSURE_DEFAULT;
+		__v4l2_ctrl_modify_range(imx214->exposure,
+					 imx214->exposure->minimum,
+					 exposure_max, imx214->exposure->step,
+					 exposure_def);
+
+		/*
+		 * Currently PPL is fixed to IMX214_PPL_DEFAULT, so hblank
+		 * depends on mode->width only, and is not changeble in any
+		 * way other than changing the mode.
+		 */
+		hblank = IMX214_PPL_DEFAULT - mode->width;
+		__v4l2_ctrl_modify_range(imx214->hblank, hblank, hblank, 1,
+					 hblank);
+	}
+
 	return 0;
 }
 
@@ -681,8 +723,25 @@  static int imx214_set_ctrl(struct v4l2_ctrl *ctrl)
 {
 	struct imx214 *imx214 = container_of(ctrl->handler,
 					     struct imx214, ctrls);
+	const struct v4l2_mbus_framefmt *format;
+	struct v4l2_subdev_state *state;
 	int ret;
 
+	state = v4l2_subdev_get_locked_active_state(&imx214->sd);
+	format = v4l2_subdev_state_get_format(state, 0);
+
+	if (ctrl->id == V4L2_CID_VBLANK) {
+		int exposure_max, exposure_def;
+
+		/* Update max exposure while meeting expected vblanking */
+		exposure_max = format->height + ctrl->val - IMX214_EXPOSURE_OFFSET;
+		exposure_def = min(exposure_max, IMX214_EXPOSURE_DEFAULT);
+		__v4l2_ctrl_modify_range(imx214->exposure,
+					 imx214->exposure->minimum,
+					 exposure_max, imx214->exposure->step,
+					 exposure_def);
+	}
+
 	/*
 	 * Applying V4L2 control value only happens
 	 * when power is up for streaming
@@ -694,7 +753,10 @@  static int imx214_set_ctrl(struct v4l2_ctrl *ctrl)
 	case V4L2_CID_EXPOSURE:
 		cci_write(imx214->regmap, IMX214_REG_EXPOSURE, ctrl->val, &ret);
 		break;
-
+	case V4L2_CID_VBLANK:
+		cci_write(imx214->regmap, IMX214_REG_FRM_LENGTH_LINES,
+			  format->height + ctrl->val, &ret);
+		break;
 	default:
 		ret = -EINVAL;
 	}
@@ -717,8 +779,11 @@  static int imx214_ctrls_init(struct imx214 *imx214)
 		.width = 1120,
 		.height = 1120,
 	};
+	const struct imx214_mode *mode = &imx214_modes[0];
 	struct v4l2_fwnode_device_properties props;
 	struct v4l2_ctrl_handler *ctrl_hdlr;
+	int exposure_max, exposure_def;
+	int hblank;
 	int ret;
 
 	ret = v4l2_fwnode_device_parse(imx214->dev, &props);
@@ -726,7 +791,7 @@  static int imx214_ctrls_init(struct imx214 *imx214)
 		return ret;
 
 	ctrl_hdlr = &imx214->ctrls;
-	ret = v4l2_ctrl_handler_init(&imx214->ctrls, 6);
+	ret = v4l2_ctrl_handler_init(&imx214->ctrls, 8);
 	if (ret)
 		return ret;
 
@@ -742,22 +807,26 @@  static int imx214_ctrls_init(struct imx214 *imx214)
 	if (imx214->link_freq)
 		imx214->link_freq->flags |= V4L2_CTRL_FLAG_READ_ONLY;
 
-	/*
-	 * WARNING!
-	 * Values obtained reverse engineering blobs and/or devices.
-	 * Ranges and functionality might be wrong.
-	 *
-	 * Sony, please release some register set documentation for the
-	 * device.
-	 *
-	 * Yours sincerely, Ricardo.
-	 */
+	/* Initial vblank/hblank/exposure parameters based on current mode */
+	imx214->vblank = v4l2_ctrl_new_std(ctrl_hdlr, &imx214_ctrl_ops,
+					   V4L2_CID_VBLANK, IMX214_VBLANK_MIN,
+					   IMX214_VTS_MAX - mode->height, 2,
+					   mode->vts_def - mode->height);
+
+	hblank = IMX214_PPL_DEFAULT - mode->width;
+	imx214->hblank = v4l2_ctrl_new_std(ctrl_hdlr, &imx214_ctrl_ops,
+					   V4L2_CID_HBLANK, hblank, hblank,
+					   1, hblank);
+	if (imx214->hblank)
+		imx214->hblank->flags |= V4L2_CTRL_FLAG_READ_ONLY;
+
+	exposure_max = mode->vts_def - IMX214_EXPOSURE_OFFSET;
+	exposure_def = min(exposure_max, IMX214_EXPOSURE_DEFAULT);
 	imx214->exposure = v4l2_ctrl_new_std(ctrl_hdlr, &imx214_ctrl_ops,
 					     V4L2_CID_EXPOSURE,
-					     IMX214_EXPOSURE_MIN,
-					     IMX214_EXPOSURE_MAX,
+					     IMX214_EXPOSURE_MIN, exposure_max,
 					     IMX214_EXPOSURE_STEP,
-					     IMX214_EXPOSURE_DEFAULT);
+					     exposure_def);
 
 	imx214->unit_size = v4l2_ctrl_new_std_compound(ctrl_hdlr,
 				NULL,
@@ -879,6 +948,12 @@  static int imx214_get_frame_interval(struct v4l2_subdev *subdev,
 	return 0;
 }
 
+/*
+ * Raw sensors should be using the VBLANK and HBLANK controls to determine
+ * the frame rate. However this driver was initially added using the
+ * [S|G|ENUM]_FRAME_INTERVAL ioctls with a fixed rate of 30fps.
+ * Retain the frame_interval ops for backwards compatibility, but they do nothing.
+ */
 static int imx214_enum_frame_interval(struct v4l2_subdev *subdev,
 				struct v4l2_subdev_state *sd_state,
 				struct v4l2_subdev_frame_interval_enum *fie)