Re: [PATCH 09/13] media: imx355: Remove redundant fll_min, and implement fixed offset

[Jacopo Mondi <jacopo.mondi@ideasonboard.com>]

Hi Dave

On Wed, May 06, 2026 at 07:23:47PM +0100, Dave Stevenson wrote:
> fll_min (Frame Length Lines) is set to the same value as fll_def
> for all modes, which makes it redundant.
>
> The actual value is also erroneous as sensor works in all the
> defined modes with FLL set at the mode height + 20 lines, so
> set the vblank control minimum to 20 rather than varying it.
> This also improves the maximum frame rate achievable.
>
> Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
> ---
>  drivers/media/i2c/imx355.c | 27 +++++----------------------
>  1 file changed, 5 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/media/i2c/imx355.c b/drivers/media/i2c/imx355.c
> index 12005bc40f36..5a3bfcd0f51c 100644
> --- a/drivers/media/i2c/imx355.c
> +++ b/drivers/media/i2c/imx355.c
> @@ -33,6 +33,8 @@
>  /* V_TIMING internal */
>  #define IMX355_REG_FLL			0x0340
>  #define IMX355_FLL_MAX			0xffff
> +/* Number of lines above frame height that are required. */
> +#define IMX355_FLL_OFFSET		20

I would have called it FFL_MIN, but it's probably just a matter of
taste
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

>
>  #define IMX355_REG_LLP			0x0342
>  #define IMX355_LLP_MAX			0xffff
> @@ -105,7 +107,6 @@ struct imx355_mode {
>
>  	/* V-timing */
>  	u32 fll_def;
> -	u32 fll_min;
>
>  	/* H-timing */
>  	u32 llp;
> @@ -360,7 +361,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 3280,
>  		.height = 2464,
>  		.fll_def = 2615,
> -		.fll_min = 2615,
>  		.llp = 3672,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_3280x2464_regs),
> @@ -376,7 +376,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 3268,
>  		.height = 2448,
>  		.fll_def = 2615,
> -		.fll_min = 2615,
>  		.llp = 3672,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_3268x2448_regs),
> @@ -392,7 +391,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 3264,
>  		.height = 2448,
>  		.fll_def = 2615,
> -		.fll_min = 2615,
>  		.llp = 3672,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_3264x2448_regs),
> @@ -408,7 +406,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1940,
>  		.height = 1096,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 3672,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1940x1096_regs),
> @@ -424,7 +421,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1936,
>  		.height = 1096,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 3672,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1936x1096_regs),
> @@ -440,7 +436,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1924,
>  		.height = 1080,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 3672,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1924x1080_regs),
> @@ -456,7 +451,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1920,
>  		.height = 1080,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 3672,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1920x1080_regs),
> @@ -472,7 +466,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1640,
>  		.height = 1232,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 1836,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1640x1232_regs),
> @@ -488,7 +481,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1640,
>  		.height = 922,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 1836,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1640x922_regs),
> @@ -504,7 +496,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1300,
>  		.height = 736,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 1836,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1300x736_regs),
> @@ -520,7 +511,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1296,
>  		.height = 736,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 1836,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1296x736_regs),
> @@ -536,7 +526,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1284,
>  		.height = 720,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 1836,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1284x720_regs),
> @@ -552,7 +541,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 1280,
>  		.height = 720,
>  		.fll_def = 1306,
> -		.fll_min = 1306,
>  		.llp = 1836,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_1280x720_regs),
> @@ -568,7 +556,6 @@ static const struct imx355_mode supported_modes[] = {
>  		.width = 820,
>  		.height = 616,
>  		.fll_def = 652,
> -		.fll_min = 652,
>  		.llp = 3672,
>  		.reg_list = {
>  			.num_of_regs = ARRAY_SIZE(mode_820x616_regs),
> @@ -857,7 +844,6 @@ imx355_set_pad_format(struct v4l2_subdev *sd,
>  	const struct imx355_mode *mode;
>  	struct v4l2_mbus_framefmt *framefmt;
>  	s32 vblank_def;
> -	s32 vblank_min;
>  	s64 h_blank;
>  	u32 height;
>
> @@ -882,10 +868,9 @@ imx355_set_pad_format(struct v4l2_subdev *sd,
>  		/* Update limits and set FPS to default */
>  		height = imx355->cur_mode->height;
>  		vblank_def = imx355->cur_mode->fll_def - height;
> -		vblank_min = imx355->cur_mode->fll_min - height;
>  		height = IMX355_FLL_MAX - height;

re-using 'height' here is not nice, but I understand it was there
already

> -		__v4l2_ctrl_modify_range(imx355->vblank, vblank_min, height, 1,
> -					 vblank_def);
> +		__v4l2_ctrl_modify_range(imx355->vblank, IMX355_FLL_OFFSET,
> +					 height, 1, vblank_def);
>  		__v4l2_ctrl_s_ctrl(imx355->vblank, vblank_def);
>  		h_blank = mode->llp - imx355->cur_mode->width;
>  		/*
> @@ -1146,7 +1131,6 @@ static int imx355_init_controls(struct imx355 *imx355)
>  	struct v4l2_ctrl_handler *ctrl_hdlr;
>  	s64 exposure_max;
>  	s64 vblank_def;
> -	s64 vblank_min;
>  	s64 hblank;
>  	u64 pixel_rate;
>  	const struct imx355_mode *mode;
> @@ -1176,9 +1160,8 @@ static int imx355_init_controls(struct imx355 *imx355)
>  	/* Initialize vblank/hblank/exposure parameters based on current mode */
>  	mode = imx355->cur_mode;
>  	vblank_def = mode->fll_def - mode->height;
> -	vblank_min = mode->fll_min - mode->height;
>  	imx355->vblank = v4l2_ctrl_new_std(ctrl_hdlr, &imx355_ctrl_ops,
> -					   V4L2_CID_VBLANK, vblank_min,
> +					   V4L2_CID_VBLANK, IMX355_FLL_OFFSET,
>  					   IMX355_FLL_MAX - mode->height,
>  					   1, vblank_def);
>
>
> --
> 2.34.1
>
>