linux-kernel - RE: [PATCH RESEND v3 3/5] drm/bridge: it6505: modify DP link auto training

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Message-ID: <e25dfcb49f5949ab9952c46a2984bbf5@ite.com.tw>
Date: Thu, 18 Sep 2025 02:23:35 +0000
From: <Hermes.Wu@....com.tw>
To: <dmitry.baryshkov@....qualcomm.com>
CC: <andrzej.hajda@...el.com>, <neil.armstrong@...aro.org>, <rfoss@...nel.org>,
        <Laurent.pinchart@...asonboard.com>, <jonas@...boo.se>,
        <jernej.skrabec@...il.com>, <maarten.lankhorst@...ux.intel.com>,
        <mripard@...nel.org>, <tzimmermann@...e.de>, <airlied@...il.com>,
        <simona@...ll.ch>, <Pet.Weng@....com.tw>, <Kenneth.Hung@....com.tw>,
        <treapking@...omium.org>, <dri-devel@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RESEND v3 3/5] drm/bridge: it6505: modify DP link auto
 training

>
>
>-----Original Message-----
>From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com> 
>Sent: Wednesday, September 17, 2025 9:47 PM
>To: Hermes Wu (吳佳宏) <Hermes.Wu@....com.tw>
>Cc: andrzej.hajda@...el.com; neil.armstrong@...aro.org; rfoss@...nel.org; Laurent.pinchart@...asonboard.com; jonas@...boo.se; jernej.skrabec@...il.com; maarten.lankhorst@...ux.intel.com; mripard@...nel.org; tzimmermann@...e.de; airlied@...il.com; simona@...ll.ch; Pet Weng (翁玉芬) <Pet.Weng@....com.tw>; Kenneth Hung (洪家倫) <Kenneth.Hung@....com.tw>; treapking@...omium.org; dri-devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org
>Subject: Re: [PATCH RESEND v3 3/5] drm/bridge: it6505: modify DP link auto training
>
>On Wed, Sep 17, 2025 at 08:37:10AM +0000, Hermes.Wu@....com.tw wrote:
>> 
>> >-----Original Message-----
>> >From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com> 
>> >Sent: Tuesday, September 16, 2025 6:49 PM
>> >To: Hermes Wu (吳佳宏) <Hermes.Wu@....com.tw>
>> >Cc: 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>; Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>; Maxime Ripard <mripard@...nel.org>; Thomas Zimmermann <tzimmermann@...e.de>; David Airlie <airlied@...il.com>; Simona Vetter <simona@...ll.ch>; Pet Weng (翁玉芬) <Pet.Weng@....com.tw>; Kenneth Hung (洪家倫) <Kenneth.Hung@....com.tw>; treapking@...omium.org; dri-devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org
>> >Subject: Re: [PATCH RESEND v3 3/5] drm/bridge: it6505: modify DP link auto training
>> >
>> >On Tue, Sep 16, 2025 at 12:47:43PM +0800, Hermes Wu via B4 Relay wrote:
>> >> From: Hermes Wu <Hermes.wu@....com.tw>
>> >> 
>> >> IT6505 supports HW link training which will write DPCD and check
>> >> training status automatically.
>> >> 
>> >> In the case that driver set link rate at 2.7G and HW fail to training,
>> >> it will change link configuration and try 1.65G. And this will cause
>> >> INT_VID_FIFO_ERROR triggered when link clock is changed.
>> >> 
>> >> When video error occurs, video logic is reset and link training restart,
>> >> this will cause endless auto link training.
>> >> 
>> >> Modify link auto training with disable INT_VID_FIFO_ERROR to avoid loop
>> >> and check INT_LINK_TRAIN_FAIL event to abort wait training done.
>> >> 
>> >> Signed-off-by: Hermes Wu <Hermes.wu@....com.tw>
>> >> ---
>> >>  drivers/gpu/drm/bridge/ite-it6505.c | 14 +++++++++++++-
>> >>  1 file changed, 13 insertions(+), 1 deletion(-)
>> >> 
>> >> diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
>> >> index 7f6227c278a51358c70a3de93454aafeef64f2bb..f9b99c70789eea6beb3c6513155c9a4ca103d219 100644
>> >> --- a/drivers/gpu/drm/bridge/ite-it6505.c
>> >> +++ b/drivers/gpu/drm/bridge/ite-it6505.c
>> >> @@ -1806,6 +1806,13 @@ static bool it6505_link_start_auto_train(struct it6505 *it6505)
>> >>  	struct device *dev = it6505->dev;
>> >>  
>> >>  	mutex_lock(&it6505->aux_lock);
>> >> +
>> >> +	/* Disable FIFO error interrupt trigger  */
>> >> +	/* to prevent training fail loop issue   */
>> >> +	it6505_set_bits(it6505, INT_MASK_03, BIT(INT_VID_FIFO_ERROR), 0);
>> >> +
>> >> +	it6505_write(it6505, INT_STATUS_03,
>> >> +		     BIT(INT_LINK_TRAIN_FAIL) | BIT(INT_VID_FIFO_ERROR));
>> >>  	it6505_set_bits(it6505, REG_TRAIN_CTRL0,
>> >>  			FORCE_CR_DONE | FORCE_EQ_DONE, 0x00);
>> >>  	/* reset link state machine and re start training*/
>> >> @@ -1818,8 +1825,10 @@ static bool it6505_link_start_auto_train(struct it6505 *it6505)
>> >>  		link_training_state = it6505_read(it6505, REG_LINK_TRAIN_STS);
>> >>  		int03 = it6505_read(it6505, INT_STATUS_03);
>> >>  		if (int03 & BIT(INT_LINK_TRAIN_FAIL)) {
>> >> +			/* Ignore INT_VID_FIFO_ERROR when auto training fail*/
>> >>  			it6505_write(it6505, INT_STATUS_03,
>> >> -				     BIT(INT_LINK_TRAIN_FAIL));
>> >> +				     BIT(INT_LINK_TRAIN_FAIL) |
>> >> +				     BIT(INT_VID_FIFO_ERROR));
>> >
>> >I'm really unusure about this change. Judging by the description of the
>> >problem, it's fix for the issue, but the issue gets introduced in the
>> >previous patch.
>> In this patch serious?
>> 
>> This patch serious fix this FIFO error issue, it change link training algorithm first then fix wrong FIFO error status.
>> 
>> The link training process start after video status is stable, and when video FIFO error occurs,
>> video stable status will also lost, link training will reset to idle and wait until video stable again.
>> 
>> IT6505 HW auto training will process link training automatically, which include CR/EQ DPCD setting, link status check,
>> and try lower link rate is the 2.7G cannot pass training.
>> 
>> In some case, DP connect to a DP sink device which cannot pass IT6505 HW auto training. 
>> when link auto training fail on 2.7G and IT6505 HW change link rate to 1.65G and retry training automatically,
>> at this time video FIFO error will occur because of the link rate change(chip issue), the video signal from SOC is not lost actually.
>
>We seems to be misunderstanding each other. I pointed out that your are
>fixing the code that was introduced in the previous patch. Would it make
>more sense to reoder or to squash the patches?

this patch can squash to previous one. they are part of auto link training fail check.

I will update in next patch serious

>> 
>> >>  
>> >>  			DRM_DEV_DEBUG_DRIVER(dev,
>> >>  					     "INT_LINK_TRAIN_FAIL(%x)!",
>> >> @@ -1837,6 +1846,9 @@ static bool it6505_link_start_auto_train(struct it6505 *it6505)
>> >>  		timeout--;
>> >>  	}
>> >>  unlock:
>> >> +	/* recover interrupt trigger*/
>> >> +	it6505_set_bits(it6505, INT_MASK_03,
>> >> +			BIT(INT_VID_FIFO_ERROR), BIT(INT_VID_FIFO_ERROR));
>> >>  	mutex_unlock(&it6505->aux_lock);
>> >>  
>> >>  	return state;
>> >> 
>> >> -- 
>> >> 2.34.1
>> >> 
>> >> 
>> >
>> >-- 
>> >With best wishes
>> >Dmitry
>> >
>> BR.
>> Hermes Wu
>
>-- 
>With best wishes
>Dmitry
>