linux-kernel - Re: [PATCH RESEND] drm/amd/display: Force link_rate as LINK_RATE

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Date:   Fri, 28 Jan 2022 13:06:52 +0000
From:   Aditya Garg <gargaditya08@...e.com>
To:     Alex Deucher <alexdeucher@...il.com>
CC:     "harry.wentland@....com" <harry.wentland@....com>,
        "sunpeng.li@....com" <sunpeng.li@....com>,
        "Rodrigo.Siqueira@....com" <Rodrigo.Siqueira@....com>,
        "alexander.deucher@....com" <alexander.deucher@....com>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "Xinhui.Pan@....com" <Xinhui.Pan@....com>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Felix.Kuehling@....com" <Felix.Kuehling@....com>,
        "evan.quan@....com" <evan.quan@....com>,
        "stylon.wang@....com" <stylon.wang@....com>,
        "wesley.chalmers@....com" <wesley.chalmers@....com>,
        "qingqing.zhuo@....com" <qingqing.zhuo@....com>,
        "George.Shen@....com" <George.Shen@....com>,
        "roman.li@....com" <roman.li@....com>,
        "solomon.chiu@....com" <solomon.chiu@....com>,
        "Aurabindo.Pillai@....com" <Aurabindo.Pillai@....com>,
        "wayne.lin@....com" <wayne.lin@....com>,
        "mikita.lipski@....com" <mikita.lipski@....com>,
        "Bhawanpreet.Lakha@....com" <Bhawanpreet.Lakha@....com>,
        "agustin.gutierrez@....com" <agustin.gutierrez@....com>,
        "pavle.kotarac@....com" <pavle.kotarac@....com>,
        Aun-Ali Zaidi <admin@...eit.net>,
        Orlando Chamberlain <redecorating@...tonmail.com>
Subject: Re: [PATCH RESEND] drm/amd/display: Force link_rate as LINK_RATE_RBR2
 for 2018 15" Apple Retina panels


Hi Alex

> On 27-Jan-2022, at 11:06 PM, Alex Deucher <alexdeucher@...il.com> wrote:
> 
> C style comments please.
Shall be fixed in v2
>  I'll let one of the display guys comment on
> the rest of the patch.  Seems reasonable, we have a similar quirk for
> the Apple MBP 2017 15" Retina panel later in this function.  Could you
> move this next to the other quirk?
I guess moving it next to the other quirk may break the functionality of this quirk, cause the MBP 2018 one involves stuff regarding firmware revision as well. The original patch applies the quirk after the following lines of the code :-

	
	core_link_read_dpcd(
		link,
		DP_SINK_HW_REVISION_START,
		(uint8_t *)&dp_hw_fw_revision,
		sizeof(dp_hw_fw_revision));

	link->dpcd_caps.sink_hw_revision =
		dp_hw_fw_revision.ieee_hw_rev;

	memmove(
		link->dpcd_caps.sink_fw_revision,
		dp_hw_fw_revision.ieee_fw_rev,
		sizeof(dp_hw_fw_revision.ieee_fw_rev));

Which seem to related to the firmware stuff. Moving it along with the 2017 quirk doesn't sound right to me, as this shall move the quirk BEFORE these lines of code instead. Maybe the author also knowingly added the quirk after these lines of code?

As a workaround, could we move the 2017 quirk later, instead of moving the 2018 quirk before? This sounds more logical to me.

Regards
Aditya