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

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Message-ID: <aWdAiaC10ear9ajR@U-2FWC9VHC-2323.local>
Date: Wed, 14 Jan 2026 15:06:49 +0800
From: Feng Tang <feng.tang@...ux.alibaba.com>
To: Sudeep Holla <sudeep.holla@....com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, 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

Hi Sudeep,

On Tue, Jan 13, 2026 at 02:40:56PM +0000, Sudeep Holla wrote:
[...]
> > > > 
> > > > With this, the root cause of the original issue was pretty obvious,
> > > > that there were some caches items missing which caused the issue when
> > > > building up scheduler domain.
> > > > 
> > > 
> > > While this may sound like a good idea, it deviates from how errors in other
> > > table-parsing code are handled. Instead of dumping the entire table, it would
> > > be preferable to report the specific issue encountered during parsing.
> > > 
> > > I do not have a strong objection if Rafael is comfortable with this approach;
> > > however, it does differ from the established pattern used by similar code.
> > > Dumping the entire table in a custom manner is not the standard way of
> > > handling parsing errors. Just my opinion.
> > 
> > Yes, it's a fair point about the error handling. Actually for the issue
> > we met, the PPTT table complies with ACPI spec and PPTT table spec nicely,
> > that it has no checksum or format issue, the only problem is some items
> > are missing. 
> > 
> 
> Agreed, but how is this any different from other tables that contain optional
> entries the ASL compiler cannot detect?
> 
> > So I would say the dump itself doesn't break any existing ACPI table error
> > handling, or change anything. As Hanjun suggested, it could be put under a
> > CONFIG_ACPI_PPTT_ERR_DUMP option as a PPTT specific debug method, and not
> > related to general ACPI table error handling.
> > 
> 
> 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.

Thanks,
Feng

> -- 
> Regards,
> Sudeep