| Message ID | 1434622954-26747-2-git-send-email-geert+renesas@glider.be (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Geert Uytterhoeven |
| Headers | show |
Hi Geert, Thank you for the patch. On Thursday 18 June 2015 12:22:33 Geert Uytterhoeven wrote: > 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 > sh_cmt. > > 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(). > > 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 > \ > /sys/devices/system/clocksource/clocksource0/current_clocksource"), > which behaves the same as before. > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> Good catch. The patch looks good to me. Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> I've quickly checked the MTU2 and TMU timer drivers and they should be immune to the issue, but I'd appreciate if you could confirm that. > --- > 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 b8ff3c64cc452a16..c96de14036a0adeb 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); > pm_genpd_syscore_poweroff(&ch->cmt->pdev->dev); > } > @@ -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; > + > pm_genpd_syscore_poweron(&ch->cmt->pdev->dev); > sh_cmt_start(ch, FLAG_CLOCKSOURCE); > }
Hi Laurent, On Thu, Jun 18, 2015 at 4:14 PM, Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote: > On Thursday 18 June 2015 12:22:33 Geert Uytterhoeven wrote: >> 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. >> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> > > Good catch. The patch looks good to me. While the solution was simple, it was hard to catch (engineers and lightbulbs... euh timers ;-) > Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Thanks! > I've quickly checked the MTU2 and TMU timer drivers and they should be immune > to the issue, but I'd appreciate if you could confirm that. I had concluded the same, thanks for verifying! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/clocksource/sh_cmt.c b/drivers/clocksource/sh_cmt.c index b8ff3c64cc452a16..c96de14036a0adeb 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); pm_genpd_syscore_poweroff(&ch->cmt->pdev->dev); } @@ -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; + pm_genpd_syscore_poweron(&ch->cmt->pdev->dev); sh_cmt_start(ch, FLAG_CLOCKSOURCE); }
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 sh_cmt. 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(). 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 > \ /sys/devices/system/clocksource/clocksource0/current_clocksource"), which behaves the same as before. Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> --- drivers/clocksource/sh_cmt.c | 6 ++++++ 1 file changed, 6 insertions(+)