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

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Date:   Tue, 15 Aug 2023 19:21:37 +0200
From:   Maxim Schwalm <maxim.schwalm@...il.com>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.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 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.

Best regards,
Maxim
View attachment "0001-drm-tegra-rgb-Parameterize-V-and-H-sync-polarities.patch" of type "text/x-patch" (1921 bytes)