linux-kernel - Re: [RFC 13/20] drm/i915/dp: Extract drm_dp_downstream_read

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Date:   Mon, 24 Aug 2020 18:46:26 +0300
From:   Imre Deak <imre.deak@...el.com>
To:     Lyude Paul <lyude@...hat.com>
Cc:     Sean Paul <sean@...rly.run>,
        Ville Syrjala <ville.syrjala@...ux.intel.com>,
        nouveau@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        open list <linux-kernel@...r.kernel.org>,
        Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
        Manasi Navare <manasi.d.navare@...el.com>,
        Uma Shankar <uma.shankar@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        José Roberto de Souza 
        <jose.souza@...el.com>, Wambui Karuga <wambui.karugax@...il.com>
Subject: Re: [RFC 13/20] drm/i915/dp: Extract drm_dp_downstream_read_info()

On Fri, Aug 21, 2020 at 01:43:39PM -0400, Lyude Paul wrote:
> [...] 
> > The wording is a bit unclear, but as I understand the Standard only
> > calls for the above:
> > 
> > """
> > A DP upstream device shall read the capability from DPCD Addresses 00080h
> > through 00083h. A DP Branch device with multiple DFPs shall report the
> > detailed
> > capability information of the lowest DFP number to which a downstream device
> > is connected, consistent with the DisplayID or legacy EDID access routing
> > policy
> > of an SST-only DP Branch device as described in Section 2.1.4.1.
> > """
> 
> So-I saw this too, but notice the use of the language "A /DP Branch/ device with
> multiple DFPs shall report the detailed…". This makes me think it's implying
> that this is a requirement for MSTBs and not SST sinks, just a guess.

Not sure either. The above could also refer to an SST branch device with
multiple DFPs (for instance a DP Replicator branch device).

--Imre