linux-kernel - Re: [PATCH] drm/msm/dp: add support of tps4 (training pattern 4) for HBR3

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Date:   Tue, 28 Dec 2021 15:12:27 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc:     robdclark@...il.com, sean@...rly.run, swboyd@...omium.org,
        vkoul@...nel.org, daniel@...ll.ch, airlied@...ux.ie,
        agross@...nel.org, dmitry.baryshkov@...aro.org,
        quic_abhinavk@...cinc.com, aravindh@...eaurora.org,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kuogee Hsieh <khsieh@...eaurora.org>
Subject: Re: [PATCH] drm/msm/dp: add support of tps4 (training pattern 4) for
 HBR3

On Tue 28 Dec 10:51 PST 2021, Kuogee Hsieh wrote:

> From: Kuogee Hsieh <khsieh@...eaurora.org>
> 
> Some DP sinkers prefer to use tps4 instead of tps3 during training #2.
> This patch will use tps4 to perform link training #2 if sinker's DPCD
> supports it.
> 
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 39558a2..c7b0657 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1181,7 +1181,7 @@ static int dp_ctrl_link_train_2(struct dp_ctrl_private *ctrl,
>  			int *training_step)
>  {
>  	int tries = 0, ret = 0;
> -	char pattern;
> +	char pattern, state_ctrl_bit;
>  	int const maximum_retries = 5;
>  	u8 link_status[DP_LINK_STATUS_SIZE];
>  
> @@ -1189,12 +1189,20 @@ static int dp_ctrl_link_train_2(struct dp_ctrl_private *ctrl,
>  
>  	*training_step = DP_TRAINING_2;
>  
> -	if (drm_dp_tps3_supported(ctrl->panel->dpcd))
> +	if (drm_dp_tps4_supported(ctrl->panel->dpcd)) {
> +		pattern = DP_TRAINING_PATTERN_4;
> +		state_ctrl_bit = 4;
> +	}
> +	else if (drm_dp_tps3_supported(ctrl->panel->dpcd)) {
>  		pattern = DP_TRAINING_PATTERN_3;
> -	else
> +		state_ctrl_bit = 3;
> +	}
> +	else {
>  		pattern = DP_TRAINING_PATTERN_2;
> +		state_ctrl_bit = 2;
> +	}
>  
> -	ret = dp_catalog_ctrl_set_pattern(ctrl->catalog, pattern);
> +	ret = dp_catalog_ctrl_set_pattern(ctrl->catalog, state_ctrl_bit);

The patch looks good, but as the state_ctrl_bit is no longer equal to
DP_PATTERN_n the function and argument names are misleading.

Please rename it to something like
"dp_catalog_ctrl_set_pattern_state_bit()" and the "pattern" argument
within that function to "state_bit".

Thanks,
Bjorn

>  	if (ret)
>  		return ret;
>  
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>