linux-kernel - Re: [PATCH 0/7] clk: qcom: gcc: Do not turn off PCIe GDSCs during gdsc

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Message-ID: <e917e98a-4ff3-45b8-87a0-fe0d6823ac2e@oss.qualcomm.com>
Date: Fri, 2 Jan 2026 14:57:56 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd
 <sboyd@...nel.org>, Taniya Das <quic_tdas@...cinc.com>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Bartosz Golaszewski
 <brgl@...nel.org>,
        Shazad Hussain <quic_shazhuss@...cinc.com>,
        Sibi Sankar <sibi.sankar@....qualcomm.com>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Melody Olvera <quic_molvera@...cinc.com>,
        Dmitry Baryshkov
 <lumag@...nel.org>,
        Taniya Das <taniya.das@....qualcomm.com>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Imran Shaik <quic_imrashai@...cinc.com>,
        Abel Vesa <abelvesa@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Rajendra Nayak <quic_rjendra@...cinc.com>,
        manivannan.sadhasivam@....qualcomm.com, stable@...r.kernel.org
Subject: Re: [PATCH 0/7] clk: qcom: gcc: Do not turn off PCIe GDSCs during
 gdsc_disable()

On 1/2/26 2:19 PM, Krishna Chaitanya Chundru wrote:
> 
> 
> On 1/2/2026 5:09 PM, Konrad Dybcio wrote:
>> On 1/2/26 12:36 PM, Krishna Chaitanya Chundru wrote:
>>>
>>> On 1/2/2026 5:04 PM, Konrad Dybcio wrote:
>>>> On 1/2/26 10:43 AM, Krishna Chaitanya Chundru wrote:
>>>>> With PWRSTS_OFF_ON, PCIe GDSCs are turned off during gdsc_disable(). This
>>>>> can happen during scenarios such as system suspend and breaks the resume
>>>>> of PCIe controllers from suspend.
>>>> Isn't turning the GDSCs off what we want though? At least during system
>>>> suspend?
>>> If we are keeping link in D3cold it makes sense, but currently we are not keeping in D3cold
>>> so we don't expect them to get off.
>> Since we seem to be tackling that in parallel, it seems to make sense
>> that adding a mechanism to let the PCIe driver select "on" vs "ret" vs
>> "off" could be useful for us
> At least I am not aware of such API where we can tell genpd not to turn off gdsc
> at runtime if we are keeping the device in D3cold state.
> But anyway the PCIe gdsc supports Retention, in that case adding this flag here makes
> more sense as it represents HW.
> sm8450,sm8650 also had similar problem which are fixed by mani[1].

Perhaps I should ask for a clarification - is retention superior to
powering the GDSC off? Does it have any power costs?

>> FWIW I recall I could turn off the GDSCs on at least makena with the old
>> suspend patches and the controllers would come back to life afterwards
> In the suspend patches, we are keeping link in D3cold, so turning off gdsc will not have any effect.

What do you mean by it won't have any effect?

> But if some reason we skipped D3cold like in S2idle case then gdsc should not be off, in that case
> in resume PCIe link will be broken.

Right, obviously

Konrad