[tip:timers/urgent] clockevents/drivers/sh_cmt: Only perform clocksource suspend/resume if enabled

From: tip-bot for Geert Uytterhoeven
Date: Sun Aug 09 2015 - 06:26:29 EST

Commit-ID: 54d46b7fbcbd00fe4b20a27208e5909facc714e3
Gitweb: http://git.kernel.org/tip/54d46b7fbcbd00fe4b20a27208e5909facc714e3
Author: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
AuthorDate: Thu, 6 Aug 2015 17:32:06 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 8 Aug 2015 10:50:08 +0200

clockevents/drivers/sh_cmt: Only perform clocksource suspend/resume if enabled

Currently the sh_cmt clocksource timer is disabled or enabled
unconditionally on clocksource suspend resp. resume, even if a
better clocksource is present (e.g. arch_sys_counter) and the
sh_cmt clocksource is not enabled.

As sh_cmt is a syscore device when its timer is enabled, this
may lead to a genpd.prepared_count imbalance in the presence of
PM Domains, which may cause a lock-up during reboot after s2ram.

During suspend:
- pm_genpd_prepare() is called for all non-syscore devices (incl.
sh_cmt), increasing genpd.prepared_count for each device,
- clocksource.suspend() is called for all clocksource devices,
- sh_cmt_clocksource_suspend() calls sh_cmt_stop(), which is a no-op
as the clocksource was not enabled.

During resume:
- clocksource.resume() is called for all clocksource devices,
- sh_cmt_clocksource_resume() calls sh_cmt_start(), which enables the
clocksource timer, and turns sh_cmt into a syscore device,
- pm_genpd_complete() is called for all non-syscore devices (excl.
sh_cmt now!), decreasing genpd.prepared_count for each device but

Now genpd.prepared_count of the PM Domain containing sh_cmt is
still 1 instead of zero. On subsequent suspend/resume cycles,
sh_cmt is still a syscore device, hence it's skipped for
pm_genpd_{prepare,complete}(), keeping the imbalance of
genpd.prepared_count at 1.

During reboot:

- platform_drv_shutdown() is called for any platform device that has
a driver with a .shutdown() method (only rcar-dmac on R-Car Gen2),

- platform_drv_shutdown() calls dev_pm_domain_detach(), which
calls genpd_dev_pm_detach(),

- genpd_dev_pm_detach() keeps calling pm_genpd_remove_device() until
it doesn't return -EAGAIN[*],

- If the device is part of the same PM Domain as sh_cmt,
pm_genpd_remove_device() always fails with -EAGAIN due to
genpd.prepared_count > 0.

- Infinite loop in genpd_dev_pm_detach()[*].

[*] Commit 93af5e9354432828 ("PM / Domains: Avoid infinite loops in
attach/detach code") already limited the number of loop iterations,
avoiding the lock-up.

To fix this, only disable or enable the clocksource timer on
clocksource suspend resp. resume if the clocksource was enabled.

This was tested on r8a7791/koelsch with the CPG Clock Domain:

- using arch_sys_counter as the clocksource, which is the default, and
which showed the problem,

- using sh_cmt as a clocksource ("echo ffca0000.timer > \
which behaves the same as before.

Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1438875126-12596-2-git-send-email-daniel.lezcano@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
drivers/clocksource/sh_cmt.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/drivers/clocksource/sh_cmt.c b/drivers/clocksource/sh_cmt.c
index b8ff3c6..c96de14 100644
--- a/drivers/clocksource/sh_cmt.c
+++ b/drivers/clocksource/sh_cmt.c
@@ -661,6 +661,9 @@ static void sh_cmt_clocksource_suspend(struct clocksource *cs)
struct sh_cmt_channel *ch = cs_to_sh_cmt(cs);

+ if (!ch->cs_enabled)
+ return;
sh_cmt_stop(ch, FLAG_CLOCKSOURCE);
@@ -669,6 +672,9 @@ static void sh_cmt_clocksource_resume(struct clocksource *cs)
struct sh_cmt_channel *ch = cs_to_sh_cmt(cs);

+ if (!ch->cs_enabled)
+ return;
sh_cmt_start(ch, FLAG_CLOCKSOURCE);
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