linux-kernel - [PATCH v2] PM: sleep: Fix runtime PM based cpuidle support

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Message-Id: <20211029123855.80344-1-ulf.hansson@linaro.org>
Date:   Fri, 29 Oct 2021 14:38:55 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     "Rafael J . Wysocki" <rafael@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-pm@...r.kernel.org
Cc:     Maulik Shah <mkshah@...eaurora.org>,
        Anup Patel <anup.patel@....com>,
        Len Brown <len.brown@...el.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] PM: sleep: Fix runtime PM based cpuidle support

In the cpuidle-psci case, runtime PM in combination with the generic PM
domain (genpd), may be used when entering/exiting a shared idlestate. More
precisely, genpd relies on runtime PM to be enabled for the attached device
(in this case it belongs to a CPU), to properly manage the reference
counting of its PM domain.

This works fine most of the time, but during system suspend in
dpm_suspend_late(), the PM core disables runtime PM for all devices. Beyond
this point, calls to pm_runtime_get_sync() to runtime resume a device may
fail and therefore it could also mess up the reference counting in genpd.

To fix this problem, let's call wake_up_all_idle_cpus() in
dpm_suspend_late(), prior to disabling runtime PM. In this way a device
that belongs to a CPU, becomes runtime resumed through cpuidle-psci and
stays like that, because the runtime PM usage count has been bumped in
device_prepare().

Diagnosed-by: Maulik Shah <mkshah@...eaurora.org>
Suggested-by: Rafael J. Wysocki <rafael@...nel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---

Changes in v2:
	- Moved away from using cpuidle_pause|resume() to solve the problem, but
	instead just waking up idle CPUs is suffient, due to other recent merged
	changes.

---
 drivers/base/power/main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index ac4dde8fdb8b..2fb08d4f1aca 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1463,6 +1463,7 @@ int dpm_suspend_late(pm_message_t state)
 	int error = 0;

 	trace_suspend_resume(TPS("dpm_suspend_late"), state.event, true);
+	wake_up_all_idle_cpus();
 	mutex_lock(&dpm_list_mtx);
 	pm_transition = state;
 	async_error = 0;
-- 
2.25.1