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

From: Jacopo Mondi

Date: Thu May 07 2026 - 10:32:19 EST

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@xxxxxxxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxxx>

>
> #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
>
>