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

From: Manaf Meethalavalappu Pallikunhi <quic_manafm@quicinc.com>
To: Konrad Dybcio <konrad.dybcio@linaro.org>,
	Priyansh Jain <quic_priyjain@quicinc.com>,
	Amit Kucheria <amitk@kernel.org>,
	Thara Gopinath <thara.gopinath@gmail.com>,
	Bjorn Andersson <andersson@kernel.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Zhang Rui <rui.zhang@intel.com>,
	Lukasz Luba <lukasz.luba@arm.com>, <linux-pm@vger.kernel.org>,
	<linux-arm-msm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<",quic_mkshah"@quicinc.com>,
	",Raghavendra Kakarla" <quic_rkakarla@quicinc.com>
Subject: Re: [PATCH] thermal/drivers/tsens: Add suspend to RAM support for tsens
Date: Sat, 27 Jan 2024 21:07:00 +0530	[thread overview]
Message-ID: <1cd754e5-fc5e-bd8b-1d70-8de40c9a85e7@quicinc.com> (raw)
In-Reply-To: <b5ea1c8c-c35d-45e3-9b90-d3dc480f4463@linaro.org>

+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