linux-kernel - Re: [PATCH 02/11] drm/bridge: tc358768: Fix bit updates

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Message-ID: <5ffb773d-5a3e-cb88-db3b-522423f2b834@ideasonboard.com>
Date:   Wed, 16 Aug 2023 11:14:43 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Maxim Schwalm <maxim.schwalm@...il.com>,
        Péter Ujfalusi <peter.ujfalusi@...il.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Francesco Dolcini <francesco@...cini.it>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Aradhya Bhatia <a-bhatia1@...com>,
        Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Svyatoslav Ryhel <clamor95@...il.com>
Subject: Re: [PATCH 02/11] drm/bridge: tc358768: Fix bit updates

On 15/08/2023 20:21, Maxim Schwalm wrote:
> On 14.08.23 08:34, Tomi Valkeinen wrote:
>> On 13/08/2023 03:23, Maxim Schwalm wrote:
>>> Hi,
>>>
>>> On 11.08.23 19:02, Tomi Valkeinen wrote:
>>>> On 11/08/2023 19:23, Péter Ujfalusi wrote:
>>>>>
>>>>>
>>>>> On 04/08/2023 13:44, Tomi Valkeinen wrote:
>>>>>> The driver has a few places where it does:
>>>>>>
>>>>>> if (thing_is_enabled_in_config)
>>>>>> 	update_thing_bit_in_hw()
>>>>>>
>>>>>> This means that if the thing is _not_ enabled, the bit never gets
>>>>>> cleared. This affects the h/vsyncs and continuous DSI clock bits.
>>>>>
>>>>> I guess the idea was to keep the reset value unless it needs to be flipped.
>>>>>
>>>>>>
>>>>>> Fix the driver to always update the bit.
>>>>>>
>>>>>> Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
>>>>>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>>>>>> ---
>>>>>>     drivers/gpu/drm/bridge/tc358768.c | 13 +++++++------
>>>>>>     1 file changed, 7 insertions(+), 6 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
>>>>>> index bc97a837955b..b668f77673c3 100644
>>>>>> --- a/drivers/gpu/drm/bridge/tc358768.c
>>>>>> +++ b/drivers/gpu/drm/bridge/tc358768.c
>>>>>> @@ -794,8 +794,8 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
>>>>>>     		val |= BIT(i + 1);
>>>>>>     	tc358768_write(priv, TC358768_HSTXVREGEN, val);
>>>>>>     
>>>>>> -	if (!(mode_flags & MIPI_DSI_CLOCK_NON_CONTINUOUS))
>>>>>> -		tc358768_write(priv, TC358768_TXOPTIONCNTRL, 0x1);
>>>>>> +	tc358768_write(priv, TC358768_TXOPTIONCNTRL,
>>>>>> +		       (mode_flags & MIPI_DSI_CLOCK_NON_CONTINUOUS) ? 0 : BIT(0));
>>>>>>     
>>>>>>     	/* TXTAGOCNT[26:16] RXTASURECNT[10:0] */
>>>>>>     	val = tc358768_to_ns((lptxcnt + 1) * dsibclk_nsk * 4);
>>>>>> @@ -861,11 +861,12 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
>>>>>>     	tc358768_write(priv, TC358768_DSI_HACT, hact);
>>>>>>     
>>>>>>     	/* VSYNC polarity */
>>>>>> -	if (!(mode->flags & DRM_MODE_FLAG_NVSYNC))
>>>>>> -		tc358768_update_bits(priv, TC358768_CONFCTL, BIT(5), BIT(5));
>>>>>> +	tc358768_update_bits(priv, TC358768_CONFCTL, BIT(5),
>>>>>> +			     (mode->flags & DRM_MODE_FLAG_PVSYNC) ? BIT(5) : 0);
>>>>>
>>>>> Was this the reverse before and should be:
>>>>> (mode->flags & DRM_MODE_FLAG_PVSYNC) ? 0 : BIT(5)
>>>>
>>>> Bit 5 is 1 for active high vsync polarity. The test was previously
>>>> !nvsync, i.e. the same as pvsync.
>>>
>>> this statement doesn't seem to be true, since this change causes a
>>> regression on the Asus TF700T. Apparently, !nvsync is true and pvsync is
>>> false in the present case.
>>
>> panasonic_vvx10f004b00_mode in panel_simple.c doesn't seem to have mode
>> flags set. I would say that means the panel doesn't care about the sync
>> polarities (which obviously is not the case), but maybe there's an
>> assumption that if sync polarities are not set, the default is...
>> positive? But I can't find any mention about this.
>>
>> Does it work for you if you set the polarities in
>> panasonic_vvx10f004b00_mode?
> 
> The panel seems to work with either negative or positive H-/Vsync in
> conjunction with the attached patch from Thierry. Currently, the display
> controller is unconditionally programmed for positive H-/Vsync though.
> What should be done in this case?
> 
> BTW, the vendor kernel configures the display controller as well as the
> bridge for negative H-/Vsync.

Ah, of course, I wasn't thinking. It's a DSI panel (obviously...), so it 
doesn't have sync polarities and as such it doesn't really make sense to 
define them in the panel-simple.c.

But we still need an agreed sync polarity between the tegra and the 
tc358768, as that is a parallel video bus. And that polarity is not 
defined anywhere, as it is expected to come from the panel.

Maybe tc358768 should have a mode-fixup, where it sets the polarities if 
they are not defined? I'll have to look at this a bit more.

  Tomi