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

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Date:   Fri, 2 Dec 2022 12:30:43 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Bjorn Andersson <andersson@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     David Airlie <airlied@...ux.ie>,
        Michael Turquette <mturquette@...libre.com>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        <linux-clk@...r.kernel.org>, Rob Clark <robdclark@...il.com>,
        Andy Gross <agross@...nel.org>, <devicetree@...r.kernel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        <linux-arm-msm@...r.kernel.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Sean Paul" <sean@...rly.run>, Stephen Boyd <sboyd@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        <krzysztof.kozlowski@...aro.org>, Daniel Vetter <daniel@...ll.ch>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        freedreno <freedreno@...ts.freedesktop.org>
Subject: Re: [Freedreno] [PATCH v7 0/6] clk/qcom: Support gdsc collapse
 polling using 'reset' interface

On 12/2/2022 4:27 AM, Bjorn Andersson 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.
>
> 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?
Correct. It doesn't need to stay there. The intention is to hit the powered-off state at least once to clear all the internal hw states (basically a hw reset).

-Akhil.
>
> Regards,
> Bjorn
>
>> This series is rebased on top of qcom/linux:for-next branch.
>>
>> Related discussion: https://patchwork.freedesktop.org/patch/493144/
>>
>> Changes in v7:
>> - Update commit message (Bjorn)
>> - Rebased on top of qcom/linux:for-next branch.
>>
>> Changes in v6:
>> - No code changes in this version. Just captured the Acked-by tags
>>
>> Changes in v5:
>> - Nit: Remove a duplicate blank line (Krzysztof)
>>
>> Changes in v4:
>> - Update gpu dt-binding schema
>> - Typo fix in commit text
>>
>> Changes in v3:
>> - Use pointer to const for "struct qcom_reset_ops" in qcom_reset_map (Krzysztof)
>>
>> Changes in v2:
>> - Return error when a particular custom reset op is not implemented. (Dmitry)
>>
>> Akhil P Oommen (6):
>>   dt-bindings: clk: qcom: Support gpu cx gdsc reset
>>   clk: qcom: Allow custom reset ops
>>   clk: qcom: gdsc: Add a reset op to poll gdsc collapse
>>   clk: qcom: gpucc-sc7280: Add cx collapse reset support
>>   dt-bindings: drm/msm/gpu: Add optional resets
>>   arm64: dts: qcom: sc7280: Add Reset support for gpu
>>
>>  .../devicetree/bindings/display/msm/gpu.yaml       |  6 +++++
>>  arch/arm64/boot/dts/qcom/sc7280.dtsi               |  3 +++
>>  drivers/clk/qcom/gdsc.c                            | 23 ++++++++++++++----
>>  drivers/clk/qcom/gdsc.h                            |  7 ++++++
>>  drivers/clk/qcom/gpucc-sc7280.c                    | 10 ++++++++
>>  drivers/clk/qcom/reset.c                           | 27 +++++++++++++++++++++-
>>  drivers/clk/qcom/reset.h                           |  8 +++++++
>>  include/dt-bindings/clock/qcom,gpucc-sc7280.h      |  3 +++
>>  8 files changed, 82 insertions(+), 5 deletions(-)
>>
>> -- 
>> 2.7.4
>>