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

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Date:   Tue, 11 Dec 2018 18:20:42 +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 11/12/2018 11:49, Jonathan Liu ha scritto:
> 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.

I don't think it is 0, because otherwise IO_POL_REG wouldn't be set to 
0x03000000 but to 0.
What is checked is exactly mode->flags, so the problem seems to be upstream.

This is my doubt, it seems mode->flags is not initialized or overriden 
at a certain point, this is why I want to debug it with Jtag tomorrow.

> 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.

0x03000000 as I've triple checked with scope means Positive H/Vsync,
and 0x00000000 Negative H/VSync.

Please check on the Thread I've pointed you above where there are all 
the links to the scope captures.

Are you completely sure you're using the correct panel?
This is because if with 0x03000000 it works correctly, it means that 
you're using Positive VS and HS but on datasheet on Figure 3.2 it shows 
that they must be negative.

Do you have any chance to measure those signals with a scope?

Tomorrow, while debugging, I'll re-check H/Vsync signals again.

Kind regards
-- 
Giulio Benetti
CTO

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