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

[Kate Hsuan]

Hi Sakari,

On Tue, Jul 28, 2026 at 3:51 PM Sakari Ailus
<sakari.ailus@xxxxxxxxxxxxxxx> wrote:
>
> Hi Kate,
>
> On Tue, Jul 28, 2026 at 02:54:49PM +0800, Kate Hsuan wrote:
> > 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.
>
> My guess is that there's something wrong with the sensor configuration if
> there are obvious systematic image defects that don't exist on other
> sensor, given the same SoftISP. Something to check indeed is the horizontal
> blanking as you've already found out. Very likely the other parameters such
> as vertical blanking could still be changed without affecting the issue.

Good suggestion. I'll try to tune vblank and possible configs and hope it works.
I scratched my head trying to find the solutions and now I can focus
on tuning the parameter to fix the issue.

>
> >
> > >
> > > 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.
>
> The PIXEL_RATE control refers to the pixel read rate in the pixel array and
> configurations where pixel rate on the CSI-2 bus differs from that are
> possible on all but the most trivial sensors (typically VGA).
>
> In this case the PLL configuration could be used to find the actual
> PIXEL_RATE (on the pixel array) as Jai mentioned.

Got it. I'll try to find a pixel rate based on the PLL settings.
Perhaps that can resolve the issue.

Thank you :)

>
> --
> Regards,
>
> Sakari Ailus
>


-- 
BR,
Kate