linux-kernel - Re: [PATCH v2 3/5] drm/bridge: it6505: modify DP link auto training

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Message-ID: <cyanpojalscyqlpvlefd5czuyd2prrstws73pmza3tecq2ha2g@aegoyfuf6na6>
Date: Sun, 30 Mar 2025 21:43:39 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: 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@....com.tw, Kenneth.Hung@....com.tw, treapking@...omium.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] drm/bridge: it6505: modify DP link auto training

On Wed, Mar 26, 2025 at 01:34:15PM +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 | 38 +++++++++++++++++++++++++++----------
>  1 file changed, 28 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
> index 0607f99446b37c82b41a376c2f4e10c7565d1b61..e0e13e737763fb801fd1cd803734a0d6ae1dd812 100644
> --- a/drivers/gpu/drm/bridge/ite-it6505.c
> +++ b/drivers/gpu/drm/bridge/ite-it6505.c
> @@ -1800,11 +1800,20 @@ static void it6505_link_training_setup(struct it6505 *it6505)
>  
>  static bool it6505_link_start_auto_train(struct it6505 *it6505)
>  {
> -	int timeout = 500, link_training_state;
> +	int link_training_state;
>  	bool state = false;
>  	int int03;
> +	struct device *dev = it6505->dev;
> +	unsigned long timeout;
> +
> +	guard(mutex)(&it6505->aux_lock);

Please don't mix functional changes and refactoring.

> +	/* 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));
>  
> -	mutex_lock(&it6505->aux_lock);
>  	it6505_set_bits(it6505, REG_TRAIN_CTRL0,
>  			FORCE_CR_DONE | FORCE_EQ_DONE, 0x00);
>  	/* reset link state machine and re start training*/
> @@ -1812,32 +1821,41 @@ static bool it6505_link_start_auto_train(struct it6505 *it6505)
>  		     FORCE_RETRAIN | MANUAL_TRAIN);
>  	it6505_write(it6505, REG_TRAIN_CTRL1, AUTO_TRAIN);
>  
> -	while (timeout > 0) {
> +	timeout = jiffies + msecs_to_jiffies(100) + 1;
> +	for (;;) {
>  		usleep_range(1000, 2000);
>  		link_training_state = it6505_read(it6505, REG_LINK_TRAIN_STS);
>  		int03 = it6505_read(it6505, INT_STATUS_03);
>  		if (int03 & BIT(INT_LINK_TRAIN_FAIL)) {
> -			it6505_write(it6505, INT_STATUS_03,
> -				     BIT(INT_LINK_TRAIN_FAIL));
> -
>  			DRM_DEV_DEBUG_DRIVER(dev,
>  					     "INT_LINK_TRAIN_FAIL(%x)!",
>  					      int03);
>  
> +			/* Ignore INT_VID_FIFO_ERROR when auto training fail*/
> +			it6505_write(it6505, INT_STATUS_03,
> +				     BIT(INT_LINK_TRAIN_FAIL) |
> +				     BIT(INT_VID_FIFO_ERROR));

Why can't it stay where it was?

> +
> +			if (int03 & BIT(INT_VID_FIFO_ERROR))
> +				DRM_DEV_DEBUG_DRIVER(dev,
> +						     "video fifo error when training fail");

Isn't the first message enough?

> +
>  			break;
>  		}
>  
>  		if (link_training_state > 0 &&
>  		    (link_training_state & LINK_STATE_NORP)) {
>  			state = true;
> -			goto unlock;
> +			break;
>  		}
>  
> -		timeout--;
> +		if (time_after(jiffies, timeout))
> +			break;
>  	}
> -unlock:
> -	mutex_unlock(&it6505->aux_lock);
>  
> +	/* recover interrupt trigger*/
> +	it6505_set_bits(it6505, INT_MASK_03,
> +			BIT(INT_VID_FIFO_ERROR), BIT(INT_VID_FIFO_ERROR));
>  	return state;
>  }
>  
> 
> -- 
> 2.34.1
> 
> 

-- 
With best wishes
Dmitry