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Date: Wed, 3 Jan 2024 09:44:42 +0000
From: Sudeep Holla <sudeep.holla@arm.com>
To: Konrad Dybcio <konrad.dybcio@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Marijn Suijten <marijn.suijten@somainline.org>,
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
	Bjorn Andersson <andersson@kernel.org>
Subject: Re: [PATCH 2/2] firmware/psci: Set
 pm_set_resume/suspend_via_firmware() on qcom
Message-ID: <20240103094442.mlh2pf3odof3ze3s@bogus>
References: <20231227-topic-psci_fw_sus-v1-0-6910add70bf3@linaro.org>
 <20231227-topic-psci_fw_sus-v1-2-6910add70bf3@linaro.org>
 <20231228102801.fzaubcjq5thfwgxg@bogus>
 <f34dd5de-9e56-4c58-b9bf-2356b41d17b1@linaro.org>
 <20231228115053.zlypgc5uxxvghi4a@bogus>
 <376d3040-b9ed-4574-90d7-fb864d694e3c@linaro.org>
 <20231228124348.mmtceqeuean7ly6y@bogus>
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In-Reply-To: <7e31d489-de96-42f0-a72a-a581859e7131@linaro.org>

On Tue, Jan 02, 2024 at 07:17:50PM +0100, Konrad Dybcio wrote:
> On 28.12.2023 13:43, Sudeep Holla wrote:
> > On Thu, Dec 28, 2023 at 01:16:28PM +0100, Konrad Dybcio wrote:
> >> On 28.12.2023 12:50, Sudeep Holla wrote:
> >>> On Thu, Dec 28, 2023 at 12:47:51PM +0100, Konrad Dybcio wrote:
> >>>> On 28.12.2023 11:28, Sudeep Holla wrote:
> >>>>> On Wed, Dec 27, 2023 at 11:15:31PM +0100, Konrad Dybcio wrote:
> >>>>>> Most Qualcomm platforms implementing PSCI (ab)use CPU_SUSPEND for
> >>>>>> entering various stages of suspend, across the SoC. These range from a
> >>>>>> simple WFI to a full-fledged power collapse of the entire chip
> >>>>>> (mostly, anyway).
> >>>>>>
> >>>>>> Some device drivers are curious to know whether "the firmware" (which is
> >>>>>> often assumed to be ACPI) takes care of suspending or resuming the
> >>>>>> platform. Set the flag that reports this behavior on the aforementioned
> >>>>>> chips.
> >>>>>>
> >>>>>> Some newer Qualcomm chips ship with firmware that actually advertises
> >>>>>> PSCI SYSTEM_SUSPEND, so the compatible list should only grow slightly.
> >>>>>>
> >>>>>
> >>>>> NACK, just use suspend-to-idle if SYSTEM_SUSPEND is not advertised. It is
> >>>>> designed for such platforms especially on x86/ACPI which don't advertise
> >>>>> Sx states. I see no reason why that doesn't work on ARM platforms as well.
> >>>>
> >>>> Not sure if I got the message through well, but the bottom line is, on
> >>>> Qualcomm platforms the "idle" states aren't actually just "idle" (read:
> >>>> they're not like S0ix). All but the most shallow ones shut down quite a
> >>>> chunk of the entire SoC, with the lowest ones being essentially S3 with
> >>>> power being cut off from the entire chip, except for the memory rail.
> >>>>
> >>>
> >>> No I understood that and S2I is exactly what you need.
> >>> Have you checked if S2I already works as intended on these platforms ?
> >> Yes, simple CPU idling works OOTB and the SoC power collapse only works
> >> given the developer doesn't cut corners when bringing up the platform
> >> (read: works on some of the ones we support, trying hard to expand that
> >> group!)
> >>
> >>> What extra do you achieve with this hack by advertising fake S2R ?
> >> Uh.. unless I misunderstood something, I'm not advertising s2ram..
> >> Quite the opposite, I'm making sure only s2idle is allowed.
> >>
> >
> > Right, I didn't notice that in suspend_valid_all(), it can be rename
> > suspend_valid_s2i or something. "All" indicates all state is valid.
> >
> > Anyways that is not the main point. IIUC S2I must still work if there is
> > at-least one CPU idle state other than WFI without these changes. Right ?
>
> Yes, and it does
>

Thanks for the confirmation.

> >
> > If all these changes is to support S2I wih WFI only, then we can look at
> > some generic solution as there were previous attempts to do something
> > similar on other platforms IIRC.
>
> No, I'm just interested in setting the resume/suspend_via_firmware()
> markers and the PSCI driver seems like a good place for it, be it on

Agreed and your PATCH 1/2 does that exactly and hence I have acked it
already.

> all platforms with SYSTEM_SUSPEND and Qualcomm which sneaked equivalent
> functionality into the CPU_SUSPEND call.
>

But I don't like the Qualcomm specific changes.

--
Regards,
Sudeep