linux-kernel - Re: [PATCH v1 2/6] dt-bindings: drm/msm/a6xx: Add GX power-domain for GMU bindings

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Message-ID: <CAF6AEGuXXqfa7OnfnyHLcyHaGXXGKHwpo4gMBH4gU0keExQcFg@mail.gmail.com>
Date:   Sun, 17 Feb 2019 17:43:16 -0500
From:   Rob Clark <robdclark@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Jordan Crouse <jcrouse@...eaurora.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v1 2/6] dt-bindings: drm/msm/a6xx: Add GX power-domain for
 GMU bindings

On Sun, Feb 17, 2019 at 4:08 PM Rob Herring <robh+dt@...nel.org> wrote:
>
> On Mon, Feb 4, 2019 at 10:15 AM Jordan Crouse <jcrouse@...eaurora.org> wrote:
> >
> > The GMU should have two power domains defined: "cx" and "gx". "cx" is the
> > actual power domain for the device and "gx" will be attached at runtime
> > to manage reference counting on the GPU device in case of a GMU crash.
>
> power-domains are supposed to be actual regions on a chip die which
> can be power gated. However, they are often abused by being defined in
> terms of kernel PM domains which are not always the same thing. This
> description sounds like the latter case.
>

iirc (and Jordan can correct me), this arrangement was needed because
normally the GMU does the GPU power control (except for if we manage
to crash it and need to reset the GMU)..

so maybe not 100% about the actual regions on chip die which can be
gated.. but it is a reality of how hw + fw + sw fit together..

BR,
-R