linux-kernel - Re: [PATCH v14.c 4/4] PCI: ACPI: Limit the Intel specific opt-in to D3 to 2024

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Message-ID: <1ff59c88-4777-4c8c-89ad-8d5030c3c8c1@amd.com>
Date:   Mon, 21 Aug 2023 14:26:22 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Iain Lane <iain@...ngesquash.org.uk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v14.c 4/4] PCI: ACPI: Limit the Intel specific opt-in to
 D3 to 2024



On 8/21/2023 2:24 PM, Rafael J. Wysocki wrote:
> On Mon, Aug 21, 2023 at 9:18 PM Limonciello, Mario
> <mario.limonciello@....com> wrote:
>>
>>
>>
>> On 8/21/2023 1:46 PM, Rafael J. Wysocki wrote:
>>> On Fri, Aug 18, 2023 at 9:40 PM Mario Limonciello
>>> <mario.limonciello@....com> wrote:
>>>>
>>>> Intel systems that need to have PCIe ports in D3 for low power idle
>>>> specify this by constraints on the ACPI PNP0D80 device. As this information
>>>> is queried by acpi_pci_bridge_d3(), limit the DMI BIOS year check to stop
>>>> at 2024. This will allow future systems to rely on the constraints check
>>>> and ACPI checks to set up policy like non-Intel systems do.
>>>
>>> So I'm not sure about the value of this change.
>>>
>>> The behavior is made Intel-specific in [14a 1/1] and it will be that
>>> way at least for some time.  This change only sets the date after
>>> which it won't be Intel-specific any more, but for what reason
>>> exactly?
>>>
>>> And why is 2024 the cut-off year (and not 2025, for example)?
>>
>> No particular reason other than it's a few kernel cycles to get this
>> tested and working or revert it if it's a bad idea after all.
>>
>>>
>>> If Intel platforms continue to be OK with putting all PCIe ports into
>>> D3hot beyond 2024, why restrict the kernel from doing so on them?
>>
>> OK let me try to explain my thought process.
>>
>> The reason that root ports were put into D3 on Intel systems was that
>> it's required for the system to get into the deepest state.
>>
>> At the time that it was introduced there wasn't a way for the firmware
>> to express this desire for root ports that were not power manageable by
>> ACPI.
>>
>> Constraints are a good way to express it, so by limiting the Intel
>> hardcode to a number of years gets everyone onto the same codepaths.
> 
> Assuming that the will be used in future systems, but that is beyond
> the control of anyone involved here I think.
> 
>> But that being said - if you would rather keep Intel as hardcode forever
>> this patch can be dropped from the series.
> 
> This change can be made at any time and I don't see a particular
> reason for making it right now.

OK, then after Bjorn reviews the other patches of 14.a and 14.c I'll 
drop this patch.

Thanks!