linux-kernel - Re: [PATCH] i2c: ACPI: Do not check ACPI_FADT_LOW_POWER

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Message-ID: <a2d2b61e-87c0-ee39-ea4e-3c575da0a66c@redhat.com>
Date:   Fri, 5 Aug 2022 20:54:45 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Limonciello, Mario" <mario.limonciello@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-input <linux-input@...r.kernel.org>,
        "rrangel@...omium.org" <rrangel@...omium.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>
Subject: Re: [PATCH] i2c: ACPI: Do not check ACPI_FADT_LOW_POWER_S0

Hi,

On 8/5/22 19:08, Rafael J. Wysocki wrote:
> On Fri, Aug 5, 2022 at 6:59 PM Limonciello, Mario
> <mario.limonciello@....com> wrote:
>>
>> On 8/5/2022 11:51, Rafael J. Wysocki wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>
>>> The ACPI_FADT_LOW_POWER_S0 flag merely means that it is better to
>>> use low-power S0 idle on the given platform than S3 (provided that
>>> the latter is supported) and it doesn't preclude using either of
>>> them (which of them will be used depends on the choices made by user
>>> space).
>>>
>>> Because of that, ACPI_FADT_LOW_POWER_S0 is generally not sufficient
>>> for making decisions in device drivers and so i2c_hid_acpi_probe()
>>> should not use it.
>>>
>>> Moreover, Linux always supports suspend-to-idle, so if a given
>>> device can wake up the system from suspend-to-idle, then it can be
>>> marked as wakeup capable unconditionally, so make that happen in
>>> i2c_hid_acpi_probe().
>>>
>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> +Raul
>> +Hans
>> +KH
>>
>> Raul had a patch that was actually going to just tear out this code
>> entirely:
>> https://lkml.kernel.org/lkml/20211220163823.1.Ie20ca47a26d3ea68124d8197b67bb1344c67f650@changeid/
>>
>> As part of that patch series discussion another suggestion had
>> transpired
>> (https://patchwork.kernel.org/project/linux-input/patch/20211220163823.2.Id022caf53d01112188308520915798f08a33cd3e@changeid/#24681016):
>>
>> ```
>> if ((acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0) &&
>>             !adev->flags.power_manageable) {
>>                  device_set_wakeup_capable(dev, true);
>>                  device_set_wakeup_enable(dev, false);
>>          }
>> ```
>>
>> If this is being changed, maybe consider that suggestion to
>> check `adev->flags.power_manageable`.
> 
> Fair enough, I'll send a v2 with this check added.

Re-reading the original thread:
https://lkml.kernel.org/lkml/20211220163823.1.Ie20ca47a26d3ea68124d8197b67bb1344c67f650@changeid/T/#u

The conclusion there was that the :

                 device_set_wakeup_capable(dev, true);
                 device_set_wakeup_enable(dev, false);

Calls should be made conditional on the IRQ being
marked ExclusiveAndWake instead of the ACPI_FADT_LOW_POWER_S0
check.

Regards,

Hans