linux-kernel - Re: [PATCH v2] ACPI: PPTT: Dump PPTT table when error detected

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Message-ID: <CAJZ5v0jRavdCW-+Ax-aC1_9EmOahhoFLatzQucZiKB9E6TtxOw@mail.gmail.com>
Date: Wed, 14 Jan 2026 15:55:31 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Feng Tang <feng.tang@...ux.alibaba.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Sudeep Holla <sudeep.holla@....com>, Len Brown <lenb@...nel.org>, 
	Jeremy Linton <jeremy.linton@....com>, Hanjun Guo <guohanjun@...wei.com>, 
	James Morse <james.morse@....com>, Joanthan Cameron <Jonathan.Cameron@...wei.com>, 
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ACPI: PPTT: Dump PPTT table when error detected

On Wed, Jan 14, 2026 at 3:28 PM Feng Tang <feng.tang@...ux.alibaba.com> wrote:
>
> On Wed, Jan 14, 2026 at 12:36:58PM +0100, Rafael J. Wysocki wrote:
> > > > Sure, that could be an option as long as CONFIG_ACPI_PPTT_ERR_DUMP is default
> > > > off and are enabled only when debugging and not always like in distro images.
> > > > Does that work for you ?
> > >
> > > Yes. It sounds great to me.
> > >
> > > > > We have had this in our tree for a while, and the good part is it gives a
> > > > > direct overview of all the processors and caches in system, you get to
> > > > > know the rough number of them from the index, and items are listed side
> > > > > by side so that some minor error could be very obvious in this comparing
> > > > > mode.
> > > > >
> > > >
> > > > Agreed, but all this info are available to userspace in some form already.
> > > > What does this dump give other than debugging a broken PPTT ?
> > >
> > > It is mainly for debugging issues. Though we locally has option to dump it
> > > on boot unconditionally to help kernel/BIOS devleoper to have a quick
> > > overview of the PPTT table, as the table gets updated from time to time,
> > > or sometime the kernel could fail before booting to user space.
> >
> > The kernel message buffer is not a great place for dumping ACPI tables though.
>
> Yes.
>
> > If an invalid PPTT prevents the system from booting, print out enough
> > information to identify the cause of the failure.
>
> Good suggestion! We do have some cases that wrong or missing info
> of some ACPI table entries cause boot failure like IORT table.
>
> As for the original issue where kernel printed the error message
> " ACPI PPTT: PPTT table found, but unable to locate core 1 (1)",
> can we just printed out all the CPU entries of the PPTT table?

As I said, print enough information to allow the problem to be
identified.  Please avoid excessive verbosity though.