linux-kernel - Re: [RFC PATCH v2 15/35] ACPI: processor: Add support for processors described as container packages

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Message-ID: <ZUTSB14JgDzFSlHK@shell.armlinux.org.uk>
Date:   Fri, 3 Nov 2023 10:57:11 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     James Morse <james.morse@....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, Salil Mehta <salil.mehta@...wei.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com
Subject: Re: [RFC PATCH v2 15/35] ACPI: processor: Add support for processors
 described as container packages

On Fri, Nov 03, 2023 at 10:43:15AM +0000, Russell King (Oracle) wrote:
> On Thu, Sep 14, 2023 at 02:53:53PM +0100, Jonathan Cameron wrote:
> > On Wed, 13 Sep 2023 16:38:03 +0000
> > James Morse <james.morse@....com> wrote:
> > 
> > > ACPI has two ways of describing processors in the DSDT. Either as a device
> > > object with HID ACPI0007, or as a type 'C' package inside a Processor
> > > Container. The ACPI processor driver probes CPUs described as devices, but
> > > not those described as packages.
> > > 
> > 
> > Specification reference needed...
> > 
> > Terminology wise, I'd just refer to Processor() objects as I think they
> > are named objects rather than data terms like a package (Which include
> > a PkgLength etc)
> 
> I'm not sure what kind of reference you want for the above. Looking in
> ACPI 6.5, I've found in 5.2.12:
> 
> "Starting with ACPI Specification 6.3, the use of the Processor() object
> was deprecated. Only legacy systems should continue with this usage. On
> the Itanium architecture only, a _UID is provided for the Processor()
> that is a string object. This usage of _UID is also deprecated since it
> can preclude an OSPM from being able to match a processor to a
> non-enumerable device, such as those defined in the MADT. From ACPI
> Specification 6.3 onward, all processor objects for all architectures
> except Itanium must now use Device() objects with an _HID of ACPI0007,
> and use only integer _UID values."
> 
> Also, there is:
> 
> https://uefi.org/specs/ACPI/6.5/08_Processor_Configuration_and_Control.html#declaring-processors
> 
> Unfortunately, using the search facility on that site to try and find
> Processor() doesn't work - it appears to strip the "()" characters from
> the search (which is completely dumb, why do search facilities do that?)
> 
> > > The missing probe for CPUs described as packages creates a problem for
> > > moving the cpu_register() calls into the acpi_processor driver, as CPUs
> > > described like this don't get registered, leading to errors from other
> > > subsystems when they try to add new sysfs entries to the CPU node.
> > > (e.g. topology_sysfs_init()'s use of topology_add_dev() via cpuhp)
> > > 
> > > To fix this, parse the processor container and call acpi_processor_add()
> > > for each processor that is discovered like this. The processor container
> > > handler is added with acpi_scan_add_handler(), so no detach call will
> > > arrive.
> > > 
> > > Qemu TCG describes CPUs using packages in a processor container.
> > 
> > processor terms in a processor container. 
> 
> Are you wanting this to be:
> 
> "Qemu TCG describes CPUs using processor terms in a processor
> container."
> 
> ? Searching the ACPI spec for "processor terms" (with or without quotes)
> only brings up results for "terms" - yet another reason to hate site-
> provided search facilities, I don't know why sites bother. :(

Given what
https://uefi.org/specs/ACPI/6.5/08_Processor_Configuration_and_Control.html#processor-container-device
says, and what QEMU does (as I detailed in my reply to Gavin), I think
this should be:

"Qemu TCG describes CPUs using processor devices in a processor
container."

which uses the same terminology as the ACPI specification. Maybe also
including a reference to the above URL would be a good idea too?

-- 
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