linux-kernel - Re: [PATCH] drm/msm/dp: Enable support for eDP v1.4+ link rates table

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Message-ID: <0e9c0f8d-c1f6-4c84-b467-37e11837882e@oss.qualcomm.com>
Date: Tue, 16 Dec 2025 16:32:44 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Dale Whinham <daleyo@...il.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar
 <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jesszhan0024@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Jérôme de Bretagne <jerome.debretagne@...il.com>,
        Steev Klimaszewski <threeway@...il.com>
Subject: Re: [PATCH] drm/msm/dp: Enable support for eDP v1.4+ link rates table

On 16/12/2025 16:31, Dale Whinham wrote:
> On 15/12/2025 22:15, Dmitry Baryshkov wrote:
>> I'd suggest following i915 and writing DP_LANE_COUNT_SET before
>> DP_LINK_BW_SET.
> 
> Thank you - made this change for v2.
> 
>>> +    /* For eDP v1.4+, parse the SUPPORTED_LINK_RATES table */
>>> +    if (link_info->revision >= DP_DPCD_REV_14) {
>>
>> No, eDP has separate versioning register. DP revision != eDP revision.
> 
> You're absolutely right, this was a mistake.
> Does something like this seem reasonable for v2?

Yes.

> 
>      if (msm_dp_panel->dpcd[DP_EDP_CONFIGURATION_CAP]) {
>          u8 edp_rev;
> 
>          rc = drm_dp_dpcd_read_byte(panel->aux, DP_EDP_DPCD_REV, &edp_rev);
>          if (rc)
>              return rc;
> 
>          if (edp_rev >= DP_EDP_14) {
>              // parse the rates
>              // ...
>          }
>      }


-- 
With best wishes
Dmitry