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

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Message-ID: <92396880-edb5-d8e0-4fcf-54aeaa2b40d7@gmail.com>
Date:   Sun, 13 Aug 2023 02:23:22 +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>
Subject: Re: [PATCH 02/11] drm/bridge: tc358768: Fix bit updates

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. 

Best regards,
Maxim