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Message-ID: <ZZV3CgnaWznmzFKF@linux.intel.com>
Date: Wed, 3 Jan 2024 16:02:34 +0100
From: Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
"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>,
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:
> > +static int hfi_pm_notify(struct notifier_block *nb,
> > + unsigned long mode, void *unused)
> > +{
> > + struct hfi_cpu_info *info = &per_cpu(hfi_cpu_info, 0);
> > + struct hfi_instance *hfi = info->hfi_instance;
> > + int ret = 0;
> > +
> > + /* HFI may not be in use. */
> > + if (!hfi)
> > + return ret;
> > +
> > + mutex_lock(&hfi_instance_lock);
> > + /*
> > + * Only handle the HFI instance of the package of the boot CPU. The
> > + * instances of other packages are handled in the CPU hotplug callbacks.
> > + */
> > + switch (mode) {
> > + case PM_HIBERNATION_PREPARE:
> > + case PM_SUSPEND_PREPARE:
> > + case PM_RESTORE_PREPARE:
> > + ret = smp_call_function_single(0, hfi_do_disable, NULL, true);
> > + break;
> > +
> > + case PM_POST_RESTORE:
> > + case PM_POST_HIBERNATION:
> > + case PM_POST_SUSPEND:
> > + ret = smp_call_function_single(0, hfi_do_enable, hfi, true);
> > + break;
>
> Because this handles the boot CPU only, one has to wonder if it should
> be a syscore op rather than a PM notifier.
>
> It does not sleep AFAICS, so it can run in that context, and it is
> guaranteed to run on the boot CPU then, so it is not necessary to
> force that. Moreover, syscore ops are guaranteed to be
> non-concurrent, so locking is not needed.
There are below warnings in smp_call_function_single() :
/*
* Can deadlock when called with interrupts disabled.
* We allow cpu's that are not yet online though, as no one else can
* send smp call function interrupt to this cpu and as such deadlocks
* can't happen.
*/
WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
&& !oops_in_progress);
/*
* When @wait we can deadlock when we interrupt between llist_add() and
* arch_send_call_function_ipi*(); when !@...t we can deadlock due to
* csd_lock() on because the interrupt context uses the same csd
* storage.
*/
WARN_ON_ONCE(!in_task());
And this one in syscore_suspend():
WARN_ONCE(!irqs_disabled(),
"Interrupts enabled before system core suspend.\n");
So seems they are not compatible.
Regards
Stanislaw
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