linux-kernel - Re: [PATCH] drm/sun4i: fix HSYNC and VSYNC polarity

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Message-ID: <CANwerB1aUP4Rw-B_qmzOu0BWmkpr-LQ5b4FKQbzZeeYHPtGoqA@mail.gmail.com>
Date:   Tue, 11 Dec 2018 21:49:13 +1100
From:   Jonathan Liu <net147@...il.com>
To:     Giulio Benetti <giulio.benetti@...ronovasrl.com>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/sun4i: fix HSYNC and VSYNC polarity

Hi Giulio,

On Thu, 6 Dec 2018 at 22:00, Giulio Benetti
<giulio.benetti@...ronovasrl.com> wrote:
>
> Hi Jonathan,
>
> Il 06/12/2018 08:29, Jonathan Liu ha scritto:
> > Hi Giulio,
> >
> > On Thu, 15 Feb 2018 at 17:54, Giulio Benetti
> > <giulio.benetti@...ronovasrl.com> wrote:
> >>
> >> Differently from other Lcd signals, HSYNC and VSYNC signals
> >> result inverted if their bits are cleared to 0.
> >>
> >> Invert their settings of IO_POL register.
> >>
> >> Signed-off-by: Giulio Benetti <giulio.benetti@...ronovasrl.com>
> >> ---
> >>   drivers/gpu/drm/sun4i/sun4i_tcon.c | 4 ++--
> >>   1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> >> index 3c15cf2..aaf911a 100644
> >> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> >> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> >> @@ -389,10 +389,10 @@ static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
> >>                       SUN4I_TCON0_BASIC3_H_SYNC(hsync));
> >>
> >>          /* Setup the polarity of the various signals */
> >> -       if (!(mode->flags & DRM_MODE_FLAG_PHSYNC))
> >> +       if (mode->flags & DRM_MODE_FLAG_PHSYNC)
> >>                  val |= SUN4I_TCON0_IO_POL_HSYNC_POSITIVE;
> >>
> >> -       if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
> >> +       if (mode->flags & DRM_MODE_FLAG_PVSYNC)
> >>                  val |= SUN4I_TCON0_IO_POL_VSYNC_POSITIVE;
> >>
> >>          regmap_update_bits(tcon->regs, SUN4I_TCON0_IO_POL_REG,
> >
> > I am running Linux 4.19.6 and noticed with Olimex LCD-OLinuXino-7TS 7"
> > LCD touchscreen (Innolux AT070TN92) connected to Olimex
> > A20-OLinuXino-MICRO that the image does not display correctly after
> > this change.
> > The image is shifted to the right.
> >
> > Reverting the change results in the image being displayed correctly on
> > the screen.
> >
> > I have in the device tree a "panel" node with compatible =
> > "innolux,at070tn92" which uses the timings in
> > drivers/gpu/drm/panel/panel-simple.c.
> >
> > Any ideas?

>
> Checking Display Datasheet:
> https://www.olimex.com/Products/Retired/A13-LCD7-TS/resources/S700-AT070TN92.pdf
>
> Page 13 section 3.3.2 you can see it needs active low VS and HS.
>
> You can refer to this Thread and check scope captures about VS and HS
> versus TCON0_IOPOL register:
> https://lists.freedesktop.org/archives/dri-devel/2018-January/163874.html
>
> There should be something that wrongly sets one of these or both:
> mode->flags |= DRM_MODE_FLAG_PHSYNC;
> and/or
> mode->flags |= DRM_MODE_FLAG_PVSYNC;
>
> Checked in panel-simple.c but it's not there.

flags is 0 because it is not assigned in the struct definition for the panel.
Before this change, TCON0_IO_POL_REG would be 0x03000000 (both bits
set to 1) and image displays correctly.
After this change, TCON0_IO_POL_REG is 0x00000000 (both bits set to 0)
and image doesn't display correctly.

Checked using "devmem2 0x01c0c088" on A20-OLinuXino-MICRO Rev J.

>
> At the moment I don't have a board to check it with me, I'll try to do
> it soon, but I'm full with other work at the moment.
>
> If you have the chance to debug you could try to find in which point
> mode->flags gets changed with those 2 flags.
>
> When the problem came out I've noticed the same thing for u-boot too but
> it's been decided to not patch it because in that case every single
> sunxi defconfig had to be changed from:
> CONFIG_VIDEO_LCD_MODE="...,sync:3,..."
> to:
> CONFIG_VIDEO_LCD_MODE="...,sync:0,..."
> and it would have been a great mess, probably not worth it:
> https://lists.denx.de/pipermail/u-boot/2018-February/321405.html
>
> So keep in mind that TCON driver works differently for HS and
> VS(inverted) polarity in u-boot and linux.
>
> Hope to work this out soon.

Regards,
Jonathan