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Message-ID: <f34dd5de-9e56-4c58-b9bf-2356b41d17b1@linaro.org>
Date: Thu, 28 Dec 2023 12:47:51 +0100
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Subject: Re: [PATCH 2/2] firmware/psci: Set
 pm_set_resume/suspend_via_firmware() on qcom
Content-Language: en-US
To: Sudeep Holla <sudeep.holla@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
 Lorenzo Pieralisi <lpieralisi@kernel.org>,
 Marijn Suijten <marijn.suijten@somainline.org>,
 linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
 Bjorn Andersson <andersson@kernel.org>
References: <20231227-topic-psci_fw_sus-v1-0-6910add70bf3@linaro.org>
 <20231227-topic-psci_fw_sus-v1-2-6910add70bf3@linaro.org>
 <20231228102801.fzaubcjq5thfwgxg@bogus>
From: Konrad Dybcio <konrad.dybcio@linaro.org>
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In-Reply-To: <20231228102801.fzaubcjq5thfwgxg@bogus>
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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.

Konrad