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

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Date:   Thu, 8 Dec 2022 21:01:41 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>
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 12/7/2022 9:30 PM, Ulf Hansson wrote:
> 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?
Explained in the other patch.

-Akhil.
>
>> 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