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: <CAJZ5v0jpWJC_9VEkXckZAPwcJESDvwncx3WzbLZn8a42U-zU1Q@mail.gmail.com>
Date:   Mon, 21 Aug 2023 21:24:33 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Limonciello, Mario" <mario.limonciello@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        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 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.