linux-kernel - Re: [PATCH RFC v3 02/21] ACPI: processor: Add support for processors described as container packages

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Date: Tue, 9 Jan 2024 15:49:15 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: 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 02/21] ACPI: processor: Add support for processors
 described as container packages

On Mon, Dec 18, 2023 at 09:17:34PM +0100, Rafael J. Wysocki wrote:
> On Wed, Dec 13, 2023 at 1:49 PM Russell King <rmk+kernel@...linux.org.uk> wrote:
> >
> > From: James Morse <james.morse@....com>
> >
> > ACPI has two ways of describing processors in the DSDT. From ACPI v6.5,
> > 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 see https://uefi.org/specs/ACPI/6.5/08_Processor_Configuration_and_Control.html#declaring-processors
> >
> > Duplicate descriptions are not allowed, the ACPI processor driver already
> > parses the UID from both devices and containers. acpi_processor_get_info()
> > returns an error if the UID exists twice in the DSDT.
> 
> I'm not really sure how the above is related to the actual patch.
> 
> > The missing probe for CPUs described as packages
> 
> It is unclear what exactly is meant by "CPUs described as packages".
> 
> From the patch, it looks like those would be Processor() objects
> defined under a processor container device.
> 
> > 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.
> 
> Discovered like what?
> 
> > The processor container
> > handler is added with acpi_scan_add_handler(), so no detach call will
> > arrive.
> 
> The above requires clarification too.

The above comments... yea. As I didn't write the commit description, but
James did, and James has basically vanished, I don't think these can be
answered, short of rewriting the entire commit message, with me spending
a lot of time with the ACPI specification trying to get the terminology
right - because at lot of the above on the face of it seems to be things
to do with wrong terminology being used.

I wasn't expecting this level of issues with this patch set, and I now
feel completely out of my depth with this series. I'm wondering whether
I should even continue with it, since I don't have the ACPI knowledge
to address a lot of these comments.

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