linux-kernel - Re: [PATCH] thermal/drivers/tsens: Add suspend to RAM support for tsens

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Date: Sat, 27 Jan 2024 21:07:00 +0530
From: Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@...aro.org>,
        Priyansh Jain
	<quic_priyjain@...cinc.com>,
        Amit Kucheria <amitk@...nel.org>,
        Thara Gopinath
	<thara.gopinath@...il.com>,
        Bjorn Andersson <andersson@...nel.org>,
        "Rafael J
 . Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>,
        <linux-pm@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <",quic_mkshah"@quicinc.com>,
        ",Raghavendra
 Kakarla" <quic_rkakarla@...cinc.com>
Subject: Re: [PATCH] thermal/drivers/tsens: Add suspend to RAM support for
 tsens

+Maulik and Raghavendra

Hi Konrad,

On 1/25/2024 4:38 PM, Konrad Dybcio wrote:
>
>
> On 1/24/24 16:25, Priyansh Jain wrote:
>>
>>
>> On 1/24/2024 6:04 PM, Konrad Dybcio wrote:
>>>
>>>
>>> On 1/24/24 11:42, Priyansh Jain wrote:
>>>>
>>>>
>>>> On 1/22/2024 8:02 PM, Konrad Dybcio wrote:
>>>>> On 22.01.2024 11:07, Priyansh Jain wrote:
>>>>>> Add suspend callback support for tsens which disables tsens 
>>>>>> interrupts
>>>>>> in suspend to RAM callback.
>>>>>
>>>>> Would it not be preferrable to have the "critical overheat", wakeup-
>>>>> capable interrupts be enabled, even if the system is suspended?
>>>>>
>>>>
>>>>
>>>> As part of suspend to RAM, tsens hardware will be turned off and it 
>>>> cannot generate any interrupt.Also system doesn't want to abort 
>>>> suspend to RAM due to tsens interrupts since system is already 
>>>> going into lowest
>>>> power state. Hence disabling tsens interrupt during suspend to RAM 
>>>> callback.
>>>
>>> Is that a hardware limitation, or a software design choice? I'm not
>>> sure I want my phone to have thermal notifications disabled when
>>> it's suspended.
>>
>>> Konrad
>>
>> As part of suspend to RAM , entire SOC will be off,
>
> What do you mean by "entire SOC[sic] will be off"? Surely the memory
> controller must be on to keep refreshing the memory? Are you thinking
> of suspend-to-disk (hibernation), by chance?

Yes, Memory will be in self refreshing  mode(Retained). But SOC will be off

and will do cold boot to come out of S2R.

>
>> this mode (suspend to RAM) is not intended for Mobile product. Tsens 
>> interrupts are not
>> disabled as part of suspend to idle(suspend mode for mobile).
>
> That's clearly untrue, e.g. the PSCI firmware on SM8550 implements
> PSCI_SYSTEM_SUSPEND, which does S2R.

IIUC, PSCI_SYSTEM_SUSPEND will be enabled only for S2R supported 
products and will be removed it for others.

Maulik/Raghavendra can comment more

>
> Konrad