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

Russell King (Oracle)
2024-01-29T14:55:41Z

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@armlinux.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?

--
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