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

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Message-ID: <2c1656ff-cba9-4122-a414-d22958f5857b@gmail.com>
Date: Tue, 16 Dec 2025 14:31:52 +0000
From: Dale Whinham <daleyo@...il.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.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 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?

	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
			// ...
		}
	}
-- 
Best regards,
Dale