RE: [PATCH v7 1/5] media: i2c: imx334: modify link frequency as for the configureation

[Shravan.Chippa]

> -----Original Message-----
> From: Jacopo Mondi <jacopo@xxxxxxxxxx>
> Sent: 19 December 2022 08:14 PM
> To: shravan Chippa - I35088 <Shravan.Chippa@xxxxxxxxxxxxx>
> Cc: paul.j.murphy@xxxxxxxxx; daniele.alessandrelli@xxxxxxxxx;
> mchehab@xxxxxxxxxx; linux-media@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v7 1/5] media: i2c: imx334: modify link frequency as for
> the configureation
> 
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> 
> Hi Shravan
> 
> On Mon, Dec 19, 2022 at 11:45:22AM +0530, shravan kumar wrote:
> > From: Shravan Chippa <shravan.chippa@xxxxxxxxxxxxx>
> >
> > Currently imx334 sensor driver is configured for 1782Mbps/lane for
> > 3840x2160@60 resolution with reqired reg mode values but if we run the
> > command "v4l2-ctl --all -d /dev/v4l-subdevX" it is showing incorrect
> > link frequeny, This is because of the incorrect value of
> > IMX334_LINK_FREQ witch is 891000000. it should be 1782000000.
> >
> > In general with the value of 891000000 link frequency it is not
> > possible to configure 3840x2160@60 resolution.
> >
> > Fixes: 9746b11715c3 ("media: i2c: Add imx334 camera sensor driver")
> >
> > Signed-off-by: Shravan Chippa <shravan.chippa@xxxxxxxxxxxxx>
> > ---
> >  drivers/media/i2c/imx334.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/i2c/imx334.c b/drivers/media/i2c/imx334.c
> > index 7b0a9086447d..acc9f9f15e47 100644
> > --- a/drivers/media/i2c/imx334.c
> > +++ b/drivers/media/i2c/imx334.c
> > @@ -49,7 +49,7 @@
> >  #define IMX334_INCLK_RATE    24000000
> >
> >  /* CSI2 HW configuration */
> > -#define IMX334_LINK_FREQ     891000000
> > +#define IMX334_LINK_FREQ     1782000000
> 
> Is this your reasoning ?
> 
> width: 3840
> hblank: 560
> height: 2160
> vblank: 2340
> bpp: 12
> fps: 60
> lanes: 4
> 
> Total bandwidth: (3840 + 560) * (2160 + 2340) * 60 * 12 = 14.256.000.000
> Bandwidth per lane = Total / 4 = 3.564.000.000 mipi clock =
> Bandwidth_per_lane / 2 = 1.782.000.000
> 
> Two questions:
> 
> - Should you update the pixel clock as well ? It is currently set to
>   594000000 while as per the above reasoning it should be doubled too.
> 
> - Where is the sensor's clock tree programmed in the driver ?
>   It's kind of weird that the pixel_clock and link_freq in the driver
>   are half of what they theoretically should be...
> 
> 
As per my understanding.
the mode_3840x2160_regs[] array value which is written through the i2c bus is 4k resolution, 60fps,  link frequency 1782Mbps per lane 
but the vblank value is dynamic from user space. 
Min-90 to Max-130000, default value is 2340. With the default value, we will get 30fps.

if we set vblank value from user space it will change FPS.

Total bandwidth: (3840 + 560) * (2160 + 2340) * 30 * 12 = 7.128.000.000
Bandwidth per lane = Total / 4 = 1.782.000.000

Thanks,
Shravan

> 
> >  #define IMX334_NUM_DATA_LANES        4
> >
> >  #define IMX334_REG_MIN               0x00
> > --
> > 2.34.1
> >