linux-kernel - Re: [PATCH v1] drm/msm/dp: do not reinitialize phy unless retry during link training

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Message-ID: <ZRvaoz7CbNncM3t6@hovoldconsulting.com>
Date:   Tue, 3 Oct 2023 11:10:59 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc:     robdclark@...il.com, sean@...rly.run, swboyd@...omium.org,
        dianders@...omium.org, vkoul@...nel.org, daniel@...ll.ch,
        airlied@...il.com, agross@...nel.org, dmitry.baryshkov@...aro.org,
        andersson@...nel.org, marijn.suijten@...ainline.org,
        quic_abhinavk@...cinc.com, quic_jesszhan@...cinc.com,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] drm/msm/dp: do not reinitialize phy unless retry
 during link training

On Tue, Aug 08, 2023 at 03:19:50PM -0700, Kuogee Hsieh wrote:
> DP PHY re-initialization done using dp_ctrl_reinitialize_mainlink() will
> cause PLL unlocked initially and then PLL gets locked at the end of
> initialization. PLL_UNLOCKED interrupt will fire during this time if the
> interrupt mask is enabled.
> However currently DP driver link training implementation incorrectly
> re-initializes PHY unconditionally during link training as the PHY was
> already configured in dp_ctrl_enable_mainlink_clocks().
> 
> Fix this by re-initializing the PHY only if the previous link training
> failed.
> 
> [drm:dp_aux_isr] *ERROR* Unexpected DP AUX IRQ 0x01000000 when not busy
> 
> Fixes: c943b4948b58 ("drm/msm/dp: add displayPort driver support")
> Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/30
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>

This fixes the above warning and avoids the unnecessary PHY power-off
and power-on during boot of the ThinkPad X13s:

Reviewed-by: Johan Hovold <johan+linaro@...nel.org>
Tested-by: Johan Hovold <johan+linaro@...nel.org>

I guess this one should go to stable as well:

Cc: stable@...r.kernel.org	# 5.10

Is anyone planning on getting this fixed in 6.6-rc? I noticed that this
one still hasn't shown up linux-next.

> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index a7a5c7e..77a8d93 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1774,13 +1774,6 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
>  		return rc;
>  
>  	while (--link_train_max_retries) {
> -		rc = dp_ctrl_reinitialize_mainlink(ctrl);
> -		if (rc) {
> -			DRM_ERROR("Failed to reinitialize mainlink. rc=%d\n",
> -					rc);
> -			break;
> -		}
> -
>  		training_step = DP_TRAINING_NONE;
>  		rc = dp_ctrl_setup_main_link(ctrl, &training_step);
>  		if (rc == 0) {
> @@ -1832,6 +1825,12 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
>  			/* stop link training before start re training  */
>  			dp_ctrl_clear_training_pattern(ctrl);
>  		}
> +
> +		rc = dp_ctrl_reinitialize_mainlink(ctrl);
> +		if (rc) {
> +			DRM_ERROR("Failed to reinitialize mainlink. rc=%d\n", rc);
> +			break;
> +		}
>  	}
>  
>  	if (ctrl->link->sink_request & DP_TEST_LINK_PHY_TEST_PATTERN)

Johan