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

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Message-ID: <Zbe8WQRASx6D6RaG@shell.armlinux.org.uk>
Date: Mon, 29 Jan 2024 14:55:21 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Rafael J. Wysocki" <rafael@...nel.org>, 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

Hi Jonathan,

On Fri, Jan 12, 2024 at 11:52:05AM +0000, Jonathan Cameron wrote:
> On Thu, 11 Jan 2024 10:26:15 +0000
> "Russell King (Oracle)" <linux@...linux.org.uk> wrote:
> > @@ -2381,16 +2388,38 @@ EXPORT_SYMBOL_GPL(acpi_dev_clear_dependencies);
> >   * acpi_dev_ready_for_enumeration - Check if the ACPI device is ready for enumeration
> >   * @device: Pointer to the &struct acpi_device to check
> >   *
> > - * Check if the device is present and has no unmet dependencies.
> > + * Check if the device is functional or enabled and has no unmet dependencies.
> >   *
> > - * Return true if the device is ready for enumeratino. Otherwise, return false.
> > + * Return true if the device is ready for enumeration. Otherwise, return false.
> >   */
> >  bool acpi_dev_ready_for_enumeration(const struct acpi_device *device)
> >  {
> >  	if (device->flags.honor_deps && device->dep_unmet)
> >  		return false;
> >  
> > -	return acpi_device_is_present(device);
> > +	/*
> > +	 * ACPI 6.5's 6.3.7 "_STA (Device Status)" allows firmware to return
> > +	 * (!present && functional) for certain types of devices that should be
> > +	 * enumerated. Note that the enabled bit should not be set unless the
> > +	 * present bit is set.
> > +	 *
> > +	 * However, limit this only to processor devices to reduce possible
> > +	 * regressions with firmware.
> > +	 */
> > +	if (device->status.functional)
> > +		return true;

I have a report from within Oracle that this causes testing failures
with QEMU using -smp cpus=2,maxcpus=4. I think it needs to be:

	if (!device->status.present)
		return device->status.functional;

	if (device->status.enabled)
		return true;

	return !acpi_device_is_processor(device);

So we can better understand the history here, let's list it as a
truth table. P=present, F=functional, E=enabled, Orig=how the code
is in mainline, James=James' original proposal, Rafael=the proposed
replacement but seems to be buggy, Rmk=the fixed version that passes
tests:

P F E	Orig	James	Rafael		Rmk
0 0 0	0	0	0		0
0 0 1	0	0	0		0
0 1 0	1	1	1		1
0 1 1	1	0	1		1
1 0 0	1	0	!processor	!processor
1 0 1	1	1	1		1
1 1 0	1	0	1		!processor
1 1 1	1	1	1		1

Any objections to this?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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