linux-kernel - Re: [PATCH v2 4/4] thermal: intel: hfi: Add a suspend notifier

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Date: Wed, 3 Jan 2024 19:04:02 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Chen Yu <yu.c.chen@...el.com>, Len Brown <len.brown@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>,
	Zhang Rui <rui.zhang@...el.com>, Zhao Liu <zhao1.liu@...el.com>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] thermal: intel: hfi: Add a suspend notifier

On Wed, Jan 03, 2024 at 02:34:26PM +0100, Rafael J. Wysocki wrote:
> The subject should say "add a PM notifier" to indicate that
> hibernation is covered too.
> 
> On Wed, Jan 3, 2024 at 5:13 AM Ricardo Neri
> <ricardo.neri-calderon@...ux.intel.com> wrote:
> >
> > The kernel gives the HFI hardware a memory region that the latter uses to
> > provide updates to the HFI table. The kernel allocates this memory region
> > at boot. It remains constant throughout runtime time.
> >
> > When resuming from suspend or hibernation, the restore kernel allocates a
> 
> The restore kernel is only used during resume from hibernation, so
> this particular problem is hibernation-specific.

Agreed. This correction is pertinent.
> 
> It is possible, at least in principle, that the address of the HFI
> table is "lost" by the processor during resume from "deep" suspend
> (ACPI S3), in which case it may not survive the firmware-driven part
> of the suspend-resume cycle.  It is thus prudent to disable HFI on
> suspend and re-enable it on resume for the boot CPU (under the
> assumption that the other CPUs will be taken care of by CPU offline),

Indeed, this patch aims to handle this scenario.

> but for a somewhat different reason than in the hibernation case.

I will correct the commit message to reflect this reasoning