linux-kernel - Re: [PATCH RFC v3 01/21] ACPI: Only enumerate enabled (or functional) devices

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Message-ID: <ZXtFBYJEX2RrFrwj@shell.armlinux.org.uk>
Date:   Thu, 14 Dec 2023 18:10:13 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev,
        x86@...nel.org, acpica-devel@...ts.linuxfoundation.org,
        linux-csky@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
        Salil Mehta <salil.mehta@...wei.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com,
        James Morse <james.morse@....com>
Subject: Re: [PATCH RFC v3 01/21] ACPI: Only enumerate enabled (or
 functional) devices

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@...wei.com> wrote:
> >
> > On Wed, 13 Dec 2023 12:49:16 +0000
> > Russell King (Oracle) <rmk+kernel@...linux.org.uk> wrote:
> >
> > > From: James Morse <james.morse@....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@....com>
> > > Tested-by: Miguel Luis <miguel.luis@...cle.com>
> > > Tested-by: Vishnu Pajjuri <vishnu@...amperecomputing.com>
> > > Tested-by: Jianyong Wu <jianyong.wu@....com>
> > > Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.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?

-- 
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