Re: [linux-sunxi] [PATCH] media: sun6i-csi: Fix incorrect HSYNC/VSYNC/PCLK polarity configuration

[Chen-Yu Tsai]

On Thu, Nov 28, 2019 at 11:51 AM OndÅej Jirman <megous@xxxxxxxxxx> wrote:
>
> On Thu, Nov 28, 2019 at 11:26:24AM +0800, Chen-Yu Tsai wrote:
> > On Thu, Nov 28, 2019 at 11:06 AM OndÅej Jirman <megous@xxxxxxxxxx> wrote:
> > >
> > > Hi,
> > >
> > > On Thu, Nov 28, 2019 at 10:26:08AM +0800, Yong wrote:
> > > > Hi Ondrej,
> > > >
> > > > This has been discussed.
> > > > And Maxime sent a patch for this:
> > > > https://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg127149.html
> > >
> > > Thanks for pointing to the previous patch. But that patch doesn't make any
> > > sense, and breaks things for me, and doesn't even match BSP code, which
> > > has no such reversal, and works fine with about 30 cam drivers.
> > >
> > > Also how do you explain my findings?
> > >
> > > My camera is sending correct signals, verified by looking at them actually (see
> > > below), and CSI is not receiving the image. I have to flip HSYNC/VSYNC to be
> > > oposite of that what CSI driver expects and I get a noisy image and if I fix
> > > PCLK polarity too, the noise goes away, which means now I'm also sampling when
> > > the data are stable and not when they're changing.
> > >
> > > Here: (output from my cam, that I configured to have VSYNC ACTIVE LOW, HSYNC
> > > ACTIVE LOW) And the signal is clearly that, as you can see yourself:
> > >
> > >   https://megous.com/dl/tmp/98df81b7ed0126ec.png
> >
> > From the looks of things you have active-high VSYNC with active-low HREF.
> > HREF is not the same as HSYNC, in fact quite the opposite. V/H SYNC are
> > pulses, active only when there should be no data and the line/frame switch
> > happens, while V/H REF are held active when there is data. I personally
> > find these terms very confusing. :(
> >
> > Now the timing diagrams in the Allwinner manuals would suggest that when
> > they are talking about H/V SYNC, they are actually referring to H/V REF.
> > The HSYNC line is high/active when there is valid data, and the VSYNC line
> > is high/active for the duration of the frame.
> >
> > I think both sides need to be checked that they are using the correct
> > polarity, and maybe also have the media maintainers clarify how the
> > polarity should be interpreted when the hardware uses H/V ref instead
> > of H/V sync.
>
> Oh my, so it's just a terminology issue? :)
>
> This probably should be docummented somewhere. I just thought xSYNC_ACTIVE_HIGH
> meant the respective signals are supposed to be HIGH during active phase of data
> transmission: that is VSYNC HIGH during entire frame, and HSYNC high during row.

Unfortunately I'm having a hard time finding a definitive source for this. My
rationale is that since the sync signal is a pulse, the active part would refer
to the pulsing part, not the at rest part.

> DT bindings documentation doesn't help much either.

Yeah. I think this should be sorted out for the whole subsystem, as this not
only affects platform drivers, but the sensor drivers as well.

> And obviously manufacturers are confused too.
>
>   https://megous.com/dl/tmp/fae07dfb4897bbb3.png

It seems at least OmniVision uses VSYNC + HREF. GalaxyCore seems to use VSYNC +
HREF as well, but they call it HSYNC, and VSYNC polarity is inverted. :(

The OV7670 sensor I was testing had an option to switch from HREF to HSYNC,
and another one to invert HREF. Talk about confusing. And HSYNC != inverted
HREF. They will be some PCLK cycles apart.

> HSYNC/VSYNC "low valid" produces what you see on the previous signal capture
> I posted. ;)

Thanks. I don't have a scope or logic analyzer. I'll wait for the people who
do to figure this out.


Regards
ChenYu

> regards,
>         o.
>
> >
> > ChenYu
> >
> > > The above signals are received with CSI driver configured with
> > > V4L2_MBUS_VSYNC_ACTIVE_HIGH V4L2_MBUS_HSYNC_ACTIVE_HIGH. So CSI driver is
> > > clearly wrong.
> > >
> > > I think this is pretty clear the driver is buggy. At least for A83T SoC.
> > >
> > > I'm not sure what Maxime found out, but he should probably re-check his
> > > findings. Maxime, can you comment on this?
> > >
> > > regards,
> > >         o.
> > >
> > > > On Thu, 28 Nov 2019 03:02:59 +0100
> > > > Ondrej Jirman <megous@xxxxxxxxxx> wrote:
> > > >
> > > > > This was discovered by writing a new camera driver and wondering, why
> > > > > hsync/vsync polarity setting behaves in reverse to what would be
> > > > > expected. Verified by looking at the actual signals and the SoC
> > > > > user manual.
> > > > >
> > > > > Fixes: 5cc7522d8965 ("media: sun6i: Add support for Allwinner CSI V3s")
> > > > > Signed-off-by: Ondrej Jirman <megous@xxxxxxxxxx>
> > > > > ---
> > > > >  drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c | 6 +++---
> > > > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > > >
> > > > > diff --git a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > > > index f17e5550602d..98bbcca59a90 100644
> > > > > --- a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > > > +++ b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
> > > > > @@ -417,12 +417,12 @@ static void sun6i_csi_setup_bus(struct sun6i_csi_dev *sdev)
> > > > >             if (flags & V4L2_MBUS_FIELD_EVEN_LOW)
> > > > >                     cfg |= CSI_IF_CFG_FIELD_POSITIVE;
> > > > >
> > > > > -           if (flags & V4L2_MBUS_VSYNC_ACTIVE_LOW)
> > > > > +           if (flags & V4L2_MBUS_VSYNC_ACTIVE_HIGH)
> > > > >                     cfg |= CSI_IF_CFG_VREF_POL_POSITIVE;
> > > > > -           if (flags & V4L2_MBUS_HSYNC_ACTIVE_LOW)
> > > > > +           if (flags & V4L2_MBUS_HSYNC_ACTIVE_HIGH)
> > > > >                     cfg |= CSI_IF_CFG_HREF_POL_POSITIVE;
> > > > >
> > > > > -           if (flags & V4L2_MBUS_PCLK_SAMPLE_RISING)
> > > > > +           if (flags & V4L2_MBUS_PCLK_SAMPLE_FALLING)
> > > > >                     cfg |= CSI_IF_CFG_CLK_POL_FALLING_EDGE;
> > > > >             break;
> > > > >     case V4L2_MBUS_BT656:
> > > > > --
> > > > > 2.24.0
> > > > >
> > > > > --
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> > > >
> > > >
> > > > Thanks,
> > > > Yong
> > >
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