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

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Message-ID: <ZZ1woQkpMMCWVnXc@shell.armlinux.org.uk>
Date: Tue, 9 Jan 2024 16:13:21 +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 Tue, Jan 09, 2024 at 05:05:15PM +0100, Rafael J. Wysocki wrote:
> On Tue, Jan 9, 2024 at 4:49 PM Russell King (Oracle)
> <linux@...linux.org.uk> wrote:
> >
> > 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.
> 
> Well, sorry about this.
> 
> I met James at the LPC last year, so he seems to be still around, in
> some way at least..

On the previous posting, I wanted James to comment on some of the
feedback from Jonathan, and despite explicitly asking, there has been
nothing but radio silence ever since James' last post of this series.

So, I now deem this work to be completely dead in the water, and not
going to happen - not unless others can input on your comments.

-- 
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