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Date:   Thu, 25 Jan 2018 16:21:17 +0100
From:   Maxime Ripard <maxime.ripard@free-electrons.com>
To:     Giulio Benetti <giulio.benetti@micronovasrl.com>
Cc:     airlied@linux.ie, wens@csie.org, dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] drm/sun4i: Handle DRM_MODE_FLAG_**SYNC_POSITIVE
 correctly
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Hi,

On Wed, Jan 24, 2018 at 08:37:28PM +0100, Giulio Benetti wrote:
> Hi,
>=20
> Il 24/01/2018 18:38, Giulio Benetti ha scritto:
> > Hi,
> >=20
> > Il 22/01/2018 21:27, Giulio Benetti ha scritto:
> > > Hi,
> > >=20
> > > Il 22/01/2018 09:51, Maxime Ripard ha scritto:
> > > > On Sat, Jan 20, 2018 at 07:50:21PM +0100, Giulio Benetti wrote:
> > > > > On previous handling, if specified DRM_MODE_FLAG_N*SYNC,
> > > > > it was ignored,
> > > > > because only PHSYNC and PVSYNC were taken into account.
> > > > > DRM_MODE_FLAG_P*SYNC and DRM_MODE_FLAG_N*SYNC are not exclusive.
> > > > >=20
> > > > > If flags contains PVSYNC, it doesn't mean it is NVSYNC.
> > > > > And it's true also the contrary.
> > > > > Also, as I've checked with scope on A20,
> > > > > if (flags & PVSYNC) then SUN4I_TCON0_IO_POL_VSYNC_POSITIVE
> > > > > must be set, as name suggests.
> > > > > It seems all display io polarities starts inverted if 0.
> > > > >=20
> > > > > Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
> > > > >=20
> > > > > PVSYNC and PHSYNC only
> > > > >=20
> > > > > Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
> > > >=20
> > > > Checkpatch:
> > > > WARNING: Duplicate signature
> > >=20
> > > Sorry I didn't use ./scripts/checkpatch.pl
> > >=20
> > > >=20
> > > > > ---
> > > > > =A0 drivers/gpu/drm/sun4i/sun4i_tcon.c | 4 ++--
> > > > > =A0 1 file changed, 2 insertions(+), 2 deletions(-)
> > > > >=20
> > > > > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > > > b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > > > index 6121210..e873a37 100644
> > > > > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > > > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > > > @@ -224,10 +224,10 @@ static void
> > > > > sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
> > > > > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 SUN4I_TCON0_BASIC3_H_S=
YNC(hsync));
> > > > > =A0=A0=A0=A0=A0 /* Setup the polarity of the various signals */
> > > > > -=A0=A0=A0 if (!(mode->flags & DRM_MODE_FLAG_PHSYNC))
> > > > > +=A0=A0=A0 if (mode->flags & DRM_MODE_FLAG_PHSYNC)
> > > > > =A0=A0=A0=A0=A0=A0=A0=A0=A0 val |=3D SUN4I_TCON0_IO_POL_HSYNC_POS=
ITIVE;
> > > > > -=A0=A0=A0 if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
> > > > > +=A0=A0=A0 if (mode->flags & DRM_MODE_FLAG_PVSYNC)
> > > > > =A0=A0=A0=A0=A0=A0=A0=A0=A0 val |=3D SUN4I_TCON0_IO_POL_VSYNC_POS=
ITIVE;
> > > >=20
> > > > I'm not sure why you were talking of the differences between NVSYNC
> > > > and PVSYNC if you're not making use of any of it here?
> > >=20
> > > Thinking about it more now, the point is that all Lcd IOs seem to be
> > > inverted by default(at least on A20).
> > > With inverted, I mean that if for example PVSYNC,
> > > I should see vsync line low and when asserted to give VSync,
> > > it goes high.
> > > This is what I've checked with oscilloscope on A20.
> > > Can someone give a try on A33? Otherwise I will,
> > > but I will take some time.
> > > On uboot, everything is treated equal to kernel,
> > > but to have my falling edge dclk and low h/vsync I had to specify:
> > > CONFIG_VIDEO_LCD_DCLK_PHASE=3D0 (giving me falling edge on dclk)
> > > and
> > > CONFIG_VIDEO_LCD_MODE=3D"....,sync:3,..."
> > > but digging into code, I see "sync:3" means H/VSYNC HIGH,
> > > but I experience both LOW during their pulse.
> > >=20
> > > >=20
> > > > Also, how was it tested? This seems quite weird that we haven't cau=
ght
> > > > that one sooner, and I'm a bit worried about the possible regressio=
ns
> > > > here.
> > >=20
> > > It sounds really strange to me too,
> > > because everybody under uboot use "sync:3"(HIGH).
> > > I will retry to measure,
> > > unfortunately at home I don't have a scope,
> > > but I think I'm going to have one soon, because of this. :)
> >=20
> > Here I am with scope captures and tcon0 registers dump:
> > tcon0_regs =3D> https://pasteboard.co/H4r8Zcs.png
> > dclk_d0 =3D> https://pasteboard.co/H4r8QRe.png
> > dclk_de =3D> https://pasteboard.co/H4r8zh4R.png
> > dclk_vsnc =3D> https://pasteboard.co/H4r8Hye.png
> >=20
> > As you can see circled in reg on registers,
> > TCON0_IO_POL_REG =3D 0x00000000.
> > But on all the waveforms you can see:
> > - dclk_d0: clock phase is 0, but it starts with falling edge, otherwise
> > the rising front overlaps dclk rising edge(not good), so to me this is
> > falling, then I mean it Negative.
> > - dclk_de: de pulse is clearly negative, even if register is 0 and its'
> > polarity bit is 0.
> > - dclk_vsnc: same as dclk_de
> > - dclk_hsync: I didn't take scope screenshot but I can assure you it's
> > negative.
> >=20
> > You can also check all the other registers about TCON0.
> >=20
> > Now I proceed testing it on A33, maybe the peripheral is slightly
> > different between Axx SoCs, if I find it that way,
> > it should be only a check about SoC or peripheral ID,
> > and treat polarity as it should be done.
>=20
> Here I am with A33 waveforms:
> tcon0_regs =3D> https://pasteboard.co/H4rXfN0M.png
> dclk_d0 =3D> https://pasteboard.co/H4rVXwy.png
> dclk_de =3D> https://pasteboard.co/H4rWDt8.png
> dclk_vsnc =3D> https://pasteboard.co/H4rWRACu.png
> dclk_hsync =3D> https://pasteboard.co/H4rWK6I.png

Thanks, that's really helpful.

> It behaves the same way as A20, so as I mean IO polarity,
> all signals(except D0-D23), are inverted.
> For A33 I've used A33-OLinuXino.
> For A20 our LiNova1.

Indeed, HSYNC and VSYNC look inverted. I don't really know what the
polarity of D0 would be just by judging at that capture, but we would
have noticed if the colors were inverted for quite some time now.

DE seems to be active high though, since it's only going to be at a
logical low level when data are not transmitted, so during the blank
periods.

Maxime

--=20
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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