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

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Date:   Fri, 25 Aug 2023 13:44:46 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, <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>
CC:     <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 8/8/2023 3:19 PM, 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.

There should be a line break here.

> 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>

I tested and confirm that without this patch, I see this spam atleast 
once per reboot but after this patch, I have not seen this for 5 
consecutive reboots.

Hence,

Tested-by: Abhinav Kumar <quic_abhinavk@...cinc.com> # sc7280

Looking at the code flow, the dp_ctrl_reinitialize_mainlink() certainly 
looks redundant where it is, considering that the clks were enabled just 
a couple of lines above in dp_ctrl_enable_mainlink_clocks().

Hence with the minor fix in the commit,

Reviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>

> ---
>   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)