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

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Message-ID: <57d929cf-4458-dae4-36d4-4e89170eba4a@micronovasrl.com>
Date:   Thu, 6 Dec 2018 12:00:11 +0100
From:   Giulio Benetti <giulio.benetti@...ronovasrl.com>
To:     Jonathan Liu <net147@...il.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 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.

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.
Best regards
-- 
Giulio Benetti
CTO

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