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

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Message-ID: <a174f4a8-42a6-c861-f08a-91fb497a5f43@quicinc.com>
Date:   Wed, 7 Dec 2022 01:28:32 +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 12:30 PM, Akhil P Oommen wrote:
> 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?
Ulf,

Gentle ping! Could you please share your feedback?

-Akhil.
>>
>>> 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
>>>