Re: [PATCH] media: i2c: imx471: Add line length PCK setting

[Kate Hsuan]

Hi Jai,

Thank you for the review.

On Tue, Jul 28, 2026 at 1:27 PM Jai Luthra <jai.luthra@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Kate,
>
> Thank you for the patch.
>
> Quoting Kate Hsuan (2026-07-28 09:50:13)
> > Add the line length PCK setting to the IMX471 driver. This parameter
> > determines the horizontal line scan duration and is used for
> > controlling the frame rate.
> >
> > Signed-off-by: Kate Hsuan <hpa@xxxxxxxxxx>
> > ---
> >  drivers/media/i2c/imx471.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/media/i2c/imx471.c b/drivers/media/i2c/imx471.c
> > index 6d358b11e96d..e661f5b78dcc 100644
> > --- a/drivers/media/i2c/imx471.c
> > +++ b/drivers/media/i2c/imx471.c
> > @@ -91,6 +91,7 @@
> >  #define IMX471_CSI_2_LANE_MODE                 1
> >  #define IMX471_CSI_4_LANE_MODE                 3
> >
> > +#define IMX471_REG_LINE_LENGTH_PCK             CCI_REG16(0x0342)
> >  #define IMX471_REG_X_ADD_STA                   CCI_REG16(0x0344)
> >  #define IMX471_REG_Y_ADD_STA                   CCI_REG16(0x0346)
> >  #define IMX471_REG_X_ADD_END                   CCI_REG16(0x0348)
> > @@ -240,6 +241,7 @@ static const struct cci_reg_sequence mode_1928x1088_regs[] = {
> >         { CCI_REG8(0x030d), 0x02 },
> >         { CCI_REG8(0x030e), 0x00 },
> >         { CCI_REG8(0x030f), 0x53 },
> > +       { IMX471_REG_LINE_LENGTH_PCK, 5008 },
>
> This does not match the mode->llp value (2328) used for 1928x1088, any idea
> why?

I tried to resolve the horizontal line pattern on the moving objects
when the sensor runs with libcamera. (The image is better for 0.7.2
and more horizontal noise for 0.7.1)
https://bugzilla.redhat.com/show_bug.cgi?id=2502786
I guess the horizontal line pattern can be mitigated by reducing the
frame rate. (image is better but the issue still happens.) I'm trying
to figure out if the root cause is in the driver or SoftISP.
If this is not the right direction for the solution, this patch can be
drop. I'll try another way to resolve it.

>
> Aside from the patch, I also see that the value for the PIXEL_RATE control
> is derived using the link-frequency and output bit-depth.
>
> It is likely that the sensor's frame rate depends solely on the LLP and FLL
> timing registers, so it should be possible to derive a constant pixel rate
> value (for a given PLL configuration) that is independent of link-freq and
> bit-depth.
The datasheet mentioned the the link frequency determines the pixel
rate so that is why pixel rate is based on link frequency.



>
> Thanks,
>     Jai
>
> >         { IMX471_REG_PLL_MULT_DRIV, IMX471_PLL_DUAL },
> >         { CCI_REG8(0x3f4c), 0x81 },
> >         { CCI_REG8(0x3f4d), 0x81 },
> > --
> > 2.55.0
> >
> >
>


-- 
BR,
Kate