linux-kernel - Re: [PATCH] drm/msm/dp: cleared DP_DOWNSPREAD_CTRL register before start link training

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Message-ID: <e7f08898-b967-f1fb-6067-5243622dd7be@quicinc.com>
Date:   Wed, 7 Sep 2022 10:42:05 -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@...ux.ie>,
        <agross@...nel.org>, <dmitry.baryshkov@...aro.org>,
        <bjorn.andersson@...aro.org>
CC:     <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] drm/msm/dp: cleared DP_DOWNSPREAD_CTRL register before
 start link training



On 9/7/2022 10:21 AM, Kuogee Hsieh wrote:
> DOWNSPREAD_CTRL (0x107) shall be cleared to 0 upon power-on reset or an
> upstream device disconnect. This patch will enforce this rule by always
> cleared DOWNPREAD_CTRL register to 0 before start link training. At rare
> case that DP MSA timing parameters may be mis-interpreted by the sinker
sinker--->sink
> which causes audio sampling rate be calculated wrongly and cause audio
> did not work at sinker if DOWNSPREAD_CTRL register is not cleared to 0.
same here
> This patch also make sure bring sinker out of D3 power-down mode into D0
> (normal operation mode) successfully by retrying 3 times.
> 
here too
> Fixes: 154b5a7da0fd ("drm/msm/dp: add displayPort driver support")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>   drivers/gpu/drm/msm/dp/dp_ctrl.c |  5 ++---
>   drivers/gpu/drm/msm/dp/dp_link.c | 17 +++++++++++------
>   2 files changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index ab6aa13..e864a6e 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1245,7 +1245,7 @@ static int dp_ctrl_link_train(struct dp_ctrl_private *ctrl,
>   {
>   	int ret = 0;
>   	const u8 *dpcd = ctrl->panel->dpcd;
> -	u8 encoding = DP_SET_ANSI_8B10B;
> +	u8 encoding[2] = {0, DP_SET_ANSI_8B10B};
>   	u8 ssc;
>   	u8 assr;
>   	struct dp_link_info link_info = {0};
> @@ -1263,8 +1263,7 @@ static int dp_ctrl_link_train(struct dp_ctrl_private *ctrl,
>   		drm_dp_dpcd_write(ctrl->aux, DP_DOWNSPREAD_CTRL, &ssc, 1);
>   	}
>   
> -	drm_dp_dpcd_write(ctrl->aux, DP_MAIN_LINK_CHANNEL_CODING_SET,
> -				&encoding, 1);
> +	drm_dp_dpcd_write(ctrl->aux, DP_DOWNSPREAD_CTRL, encoding, 2);
>   

This seems wrong.

This will override the value programmed by the above piece of code.

         if (drm_dp_max_downspread(dpcd)) {
                 ssc = DP_SPREAD_AMP_0_5;
                 drm_dp_dpcd_write(ctrl->aux, DP_DOWNSPREAD_CTRL, &ssc, 1);
         }

Perhaps, you should have an else case to the above if and program 0 only 
for those cases?

>   	if (drm_dp_alternate_scrambler_reset_cap(dpcd)) {
>   		assr = DP_ALTERNATE_SCRAMBLER_RESET_ENABLE;
> diff --git a/drivers/gpu/drm/msm/dp/dp_link.c b/drivers/gpu/drm/msm/dp/dp_link.c
> index 36f0af0..3ad3826 100644
> --- a/drivers/gpu/drm/msm/dp/dp_link.c
> +++ b/drivers/gpu/drm/msm/dp/dp_link.c
> @@ -49,7 +49,7 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
>   					struct dp_link_info *link)
>   {
>   	u8 value;
> -	int err;
> +	int i, err;
>   
>   	if (link->revision < 0x11)
>   		return 0;
> @@ -61,11 +61,16 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
>   	value &= ~DP_SET_POWER_MASK;
>   	value |= DP_SET_POWER_D0;
>   
> -	err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
> -	if (err < 0)
> -		return err;
> -
> -	usleep_range(1000, 2000);
> +	/*
> +	 * When turning on, we need to retry for 1ms to give the sink
> +	 * time to wake up.
> +	 */
> +	for (i = 0; i < 3; i++) {
> +	        err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
> +		usleep_range(1000, 2000);
> +		if (err == 1)
> +			break;
> +	}
>   
>   	return 0;
>   }