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Subject: Re: [PATCH 2/2] drm/sun4i: Handle DRM_MODE_FLAG_**SYNC_POSITIVE
 correctly
To:     Maxime Ripard <maxime.ripard@free-electrons.com>
Cc:     airlied@linux.ie, wens@csie.org, dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
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From:   Giulio Benetti <giulio.benetti@micronovasrl.com>
Message-ID: <18ec71dc-a785-a771-76d4-176d95032c97@micronovasrl.com>
Date:   Fri, 26 Jan 2018 16:55:54 +0100
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Hi,

Il 26/01/2018 15:56, Maxime Ripard ha scritto:
> On Thu, Jan 25, 2018 at 05:50:18PM +0100, Giulio Benetti wrote:
>>>>>>> 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.
>>>>>>>>
>>>>>>>> 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.
>>>>>>>>
>>>>>>>> Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
>>>>>>>>
>>>>>>>> PVSYNC and PHSYNC only
>>>>>>>>
>>>>>>>> Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
>>>>>>>
>>>>>>> Checkpatch:
>>>>>>> WARNING: Duplicate signature
>>>>>>
>>>>>> Sorry I didn't use ./scripts/checkpatch.pl
>>>>>>
>>>>>>>
>>>>>>>> ---
>>>>>>>>   ? 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 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,
>>>>>>>>   ?????????????? 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;
>>>>>>>
>>>>>>> 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?
>>>>>>
>>>>>> 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=0 (giving me falling edge on dclk)
>>>>>> and
>>>>>> CONFIG_VIDEO_LCD_MODE="....,sync:3,..."
>>>>>> but digging into code, I see "sync:3" means H/VSYNC HIGH,
>>>>>> but I experience both LOW during their pulse.
>>>>>>
>>>>>>>
>>>>>>> Also, how was it tested? This seems quite weird that we haven't caught
>>>>>>> that one sooner, and I'm a bit worried about the possible regressions
>>>>>>> here.
>>>>>>
>>>>>> 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. :)
>>>>>
>>>>> Here I am with scope captures and tcon0 registers dump:
>>>>> tcon0_regs => https://pasteboard.co/H4r8Zcs.png
>>>>> dclk_d0 => https://pasteboard.co/H4r8QRe.png
>>>>> dclk_de => https://pasteboard.co/H4r8zh4R.png
>>>>> dclk_vsnc => https://pasteboard.co/H4r8Hye.png
>>>>>
>>>>> As you can see circled in reg on registers,
>>>>> TCON0_IO_POL_REG = 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.
>>>>>
>>>>> You can also check all the other registers about TCON0.
>>>>>
>>>>> 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.
>>>>
>>>> Here I am with A33 waveforms:
>>>> tcon0_regs => https://pasteboard.co/H4rXfN0M.png
>>>> dclk_d0 => https://pasteboard.co/H4rVXwy.png
>>>> dclk_de => https://pasteboard.co/H4rWDt8.png
>>>> dclk_vsnc => https://pasteboard.co/H4rWRACu.png
>>>> dclk_hsync => 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.
>>
>> Yes, so they should be inverted inside the driver.
> 
> Yep. And the LCD panels used on our boards as well in order to avoid
> any breakages.

Can you provide a list?
Or is there a way I can find it on my own?
I can create a whole patch-set providing this too on panel-simple.c
Ok?

> 
>>> 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.
>>
>> D0-D23 are correct.
>>
>> With that capture, I mean to show you instead dclk is inverted, as
>> dclk samples D0 on falling edge.
> 
> Ah right, DCLK being the first channel?

Yes, sorry I didn't place a label on channels

> 
>> So 0 is NEGEDGE and 1 is POSEDGE(1/3 of clock phase).
>> 1/3 clock phase seems enough to me to be considered POSEDGE,
>> 2/3 instead risks to go too much to the right of D0(even if it could work).
> 
> Do you have captures with both settings?

Not now, but asap I'm going to take.

> 
>>> 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.
>>
>> Yes, you're right, DE is data enable, and is asserted high as 0.
> 
> No, it is asserted high as 1

Sorry, I wanted to tell it is asserted high with IO_POL register bit 
cleared to 0. So we're saying same thing now.

> 
>> But it must be added.
>> I'm planning to send a new patchset with all these things corrected for
>> kernel.
> 
> Ok.
> 
>> A little out of thread but:
>> I'd like to send one for u-boot too,
>> but this means also to modify every sunxi "sync:3" to "sync:0" and
>> vice-versa.
>>
>> What do you think?
> 
> That it's going to be a nightmare... We've advertised since the very
> beginning something, and we're about to break it. I'm not sure we want
> to do that.

I can take care about that.
But I also think that a lot of displays work because they use only 
DE-mode, almost ignoring HSync and VSync signals(HV-mode).

In any case I have to produce these patches because of my company's 
board based on A20 and A33, and modify defconfig according to it.
The only technical nightmare I see is to produce a commit for every 
defconfig to be modified and copy-paste che commit-log substituing board 
name(1-2 days of work).
Problem is testing, but we're speaking about something that probably was 
badly working, but you couldn't see it on display.
So I think this is only an improvement at the end.

I'm sorry I've taken bad news.
Drink 1 glass of Spritz to go over! :)

> 
> Thanks!
> Maxime
> 


-- 
Giulio Benetti
R&D Manager &
Advanced Research

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