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

[Dave Stevenson]

Hi Jacopo

On Thu, 7 May 2026 at 15:29, Jacopo Mondi <jacopo.mondi@xxxxxxxxxxxxxxxx> wrote:
>
> 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

It's not the minimum value for the FFL register though as that
includes the image height.
It could be IMX355_VBLANK_MIN if preferred.

  Dave

> 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
> >
> >