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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Thu, 14 Dec 2023 19:16:02 +0100
Message-ID: <CAJZ5v0h2Keyb-gFWFuPsKtwqjXvM2snyGpo6MMfFzaXKbfEpgw@mail.gmail.com>
Subject: Re: [PATCH RFC v3 01/21] ACPI: Only enumerate enabled (or functional) devices
To:     "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        linux-pm@vger.kernel.org, loongarch@lists.linux.dev,
        linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev,
        x86@kernel.org, acpica-devel@lists.linuxfoundation.org,
        linux-csky@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org,
        Salil Mehta <salil.mehta@huawei.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        jianyong.wu@arm.com, justin.he@arm.com,
        James Morse <james.morse@arm.com>
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On Thu, Dec 14, 2023 at 7:10 PM Russell King (Oracle)
<linux@armlinux.org.uk> wrote:
>
> On Thu, Dec 14, 2023 at 06:47:00PM +0100, Rafael J. Wysocki wrote:
> > On Thu, Dec 14, 2023 at 6:32 PM Jonathan Cameron
> > <Jonathan.Cameron@huawei.com> wrote:
> > >
> > > On Wed, 13 Dec 2023 12:49:16 +0000
> > > Russell King (Oracle) <rmk+kernel@armlinux.org.uk> wrote:
> > >
> > > > From: James Morse <james.morse@arm.com>
> > > >
> > > > Today the ACPI enumeration code 'visits' all devices that are present.
> > > >
> > > > This is a problem for arm64, where CPUs are always present, but not
> > > > always enabled. When a device-check occurs because the firmware-policy
> > > > has changed and a CPU is now enabled, the following error occurs:
> > > > | acpi ACPI0007:48: Enumeration failure
> > > >
> > > > This is ultimately because acpi_dev_ready_for_enumeration() returns
> > > > true for a device that is not enabled. The ACPI Processor driver
> > > > will not register such CPUs as they are not 'decoding their resources'.
> > > >
> > > > Change acpi_dev_ready_for_enumeration() to also check the enabled bit.
> > > > ACPI allows a device to be functional instead of maintaining the
> > > > present and enabled bit. Make this behaviour an explicit check with
> > > > a reference to the spec, and then check the present and enabled bits.
> > > > This is needed to avoid enumerating present && functional devices that
> > > > are not enabled.
> > > >
> > > > Signed-off-by: James Morse <james.morse@arm.com>
> > > > Tested-by: Miguel Luis <miguel.luis@oracle.com>
> > > > Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> > > > Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> > > > Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > > > ---
> > > > If this change causes problems on deployed hardware, I suggest an
> > > > arch opt-in: ACPI_IGNORE_STA_ENABLED, that causes
> > > > acpi_dev_ready_for_enumeration() to only check the present bit.
> > >
> > > My gut feeling (having made ACPI 'fixes' in the past that ran into
> > > horribly broken firmware and had to be reverted) is reduce the blast
> > > radius preemptively from the start. I'd love to live in a world were
> > > that wasn't necessary but I don't trust all the generators of ACPI tables.
> > > I'll leave it to Rafael and other ACPI experts suggest how narrow we should
> > > make it though - arch opt in might be narrow enough.
> >
> > A chicken bit wouldn't help much IMO, especially in the cases when
> > working setups get broken.
> >
> > I would very much prefer to limit the scope of it, say to processors
> > only, in the first place.
>
> Thanks for the feedback and the idea.
>
> I guess we need something like:
>
>         if (device->status.present)
>                 return device->device_type != ACPI_BUS_TYPE_PROCESSOR ||
>                        device->status.enabled;
>         else
>                 return device->status.functional;
>
> so we only check device->status.enabled for processor-type devices?

Yes, something like this.