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

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Message-ID: <2bk6t2uibhbqtreavimigffzp746rnui4ohqk6sxcpolf4skjh@ddyma4omo6k7>
Date: Tue, 16 Sep 2025 13:48:34 +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 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.

>  
>  			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