linux-kernel - Re: [PATCH v7 0/6] clk/qcom: Support gdsc collapse polling using 'reset' interface

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Date:   Wed, 7 Dec 2022 17:00:51 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Bjorn Andersson <andersson@...nel.org>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc:     freedreno <freedreno@...ts.freedesktop.org>,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Douglas Anderson <dianders@...omium.org>,
        krzysztof.kozlowski@...aro.org,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>, Sean Paul <sean@...rly.run>,
        Stephen Boyd <sboyd@...nel.org>, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 0/6] clk/qcom: Support gdsc collapse polling using
 'reset' interface

On Thu, 1 Dec 2022 at 23:57, Bjorn Andersson <andersson@...nel.org> wrote:
>
> On Wed, Oct 05, 2022 at 02:36:58PM +0530, Akhil P Oommen wrote:
> >
>
> @Ulf, Akhil has a power-domain for a piece of hardware which may be
> voted active by multiple different subsystems (co-processors/execution
> contexts) in the system.
>
> As such, during the powering down sequence we don't wait for the
> power-domain to turn off. But in the event of an error, the recovery
> mechanism relies on waiting for the hardware to settle in a powered off
> state.
>
> The proposal here is to use the reset framework to wait for this state
> to be reached, before continuing with the recovery mechanism in the
> client driver.

I tried to review the series (see my other replies), but I am not sure
I fully understand the consumer part.

More exactly, when and who is going to pull the reset and at what point?

>
> Given our other discussions on quirky behavior, do you have any
> input/suggestions on this?
>
> > Some clients like adreno gpu driver would like to ensure that its gdsc
> > is collapsed at hardware during a gpu reset sequence. This is because it
> > has a votable gdsc which could be ON due to a vote from another subsystem
> > like tz, hyp etc or due to an internal hardware signal. To allow
> > this, gpucc driver can expose an interface to the client driver using
> > reset framework. Using this the client driver can trigger a polling within
> > the gdsc driver.
>
> @Akhil, this description is fairly generic. As we've reached the state
> where the hardware has settled and we return to the client, what
> prevents it from being powered up again?
>
> Or is it simply a question of it hitting the powered-off state, not
> necessarily staying there?

Okay, so it's indeed the GPU driver that is going to assert/de-assert
the reset at some point. Right?

That seems like a reasonable approach to me, even if it's a bit
unclear under what conditions that could happen.

[...]

Kind regards
Uffe