| Message ID | 1380647718-9178-3-git-send-email-Dave.Martin@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 1 Oct 2013, Dave Martin wrote: > CPU hotplug and kexec rely on smp_ops.cpu_kill(), which is supposed > to wait for the CPU to park or power down, and perform the last > rites (such as disabling clocks etc., where the platform doesn't do > this automatically). > > kexec in particular is unsafe without performing this > synchronisation to park secondaries. Without it, the secondaries > might not be parked when kexec trashes the kernel. > > There is no generic way to do this synchronisation, so a new mcpm > platform_ops method power_down_finish() is added by this patch. > > The new method is mandatory. A platform which provides no way to > detect when CPUs are parked is likely broken. > > Signed-off-by: Dave Martin <Dave.Martin@arm.com> Reviewed-by: Nicolas Pitre <nico@linaro.org> > --- > arch/arm/common/mcpm_entry.c | 15 +++++++++++++++ > arch/arm/common/mcpm_platsmp.c | 10 ++++++++++ > arch/arm/include/asm/mcpm.h | 31 +++++++++++++++++++++++++++++++ > 3 files changed, 56 insertions(+) > > diff --git a/arch/arm/common/mcpm_entry.c b/arch/arm/common/mcpm_entry.c > index 9902509..6c03d01 100644 > --- a/arch/arm/common/mcpm_entry.c > +++ b/arch/arm/common/mcpm_entry.c > @@ -90,6 +90,21 @@ void mcpm_cpu_power_down(void) > BUG(); > } > > +int mcpm_cpu_power_down_finish(unsigned int cpu, unsigned int cluster) > +{ > + int ret; > + > + if (WARN_ON_ONCE(!platform_ops || !platform_ops->power_down_finish)) > + return -EUNATCH; > + > + ret = platform_ops->power_down_finish(cpu, cluster); > + if (ret) > + pr_warn("%s: cpu %u, cluster %u failed to power down (%d)\n", > + __func__, cpu, cluster, ret); > + > + return ret; > +} > + > void mcpm_cpu_suspend(u64 expected_residency) > { > phys_reset_t phys_reset; > diff --git a/arch/arm/common/mcpm_platsmp.c b/arch/arm/common/mcpm_platsmp.c > index c0c3cd7..177251a 100644 > --- a/arch/arm/common/mcpm_platsmp.c > +++ b/arch/arm/common/mcpm_platsmp.c > @@ -56,6 +56,15 @@ static void mcpm_secondary_init(unsigned int cpu) > > #ifdef CONFIG_HOTPLUG_CPU > > +static int mcpm_cpu_kill(unsigned int cpu) > +{ > + unsigned int pcpu, pcluster; > + > + cpu_to_pcpu(cpu, &pcpu, &pcluster); > + > + return !mcpm_cpu_power_down_finish(pcpu, pcluster); > +} > + > static int mcpm_cpu_disable(unsigned int cpu) > { > /* > @@ -82,6 +91,7 @@ static struct smp_operations __initdata mcpm_smp_ops = { > .smp_boot_secondary = mcpm_boot_secondary, > .smp_secondary_init = mcpm_secondary_init, > #ifdef CONFIG_HOTPLUG_CPU > + .cpu_kill = mcpm_cpu_kill, > .cpu_disable = mcpm_cpu_disable, > .cpu_die = mcpm_cpu_die, > #endif > diff --git a/arch/arm/include/asm/mcpm.h b/arch/arm/include/asm/mcpm.h > index fc82a88..1cf2601 100644 > --- a/arch/arm/include/asm/mcpm.h > +++ b/arch/arm/include/asm/mcpm.h > @@ -81,10 +81,40 @@ int mcpm_cpu_power_up(unsigned int cpu, unsigned int cluster); > * > * This will return if mcpm_platform_register() has not been called > * previously in which case the caller should take appropriate action. > + * > + * On success, the CPU is not guaranteed to be truly halted until > + * mcpm_cpu_power_down_finish() subsequently returns non-zero for the > + * specified cpu. Until then, other CPUs should make sure they do not > + * trash memory the target CPU might be executing/accessing. > */ > void mcpm_cpu_power_down(void); > > /** > + * mcpm_cpu_power_down_finish - wait for a specified CPU to halt, and > + * make sure it is powered off > + * > + * @cpu: CPU number within given cluster > + * @cluster: cluster number for the CPU > + * > + * Call this function to ensure that a pending powerdown has taken > + * effect and the CPU is safely parked before performing non-mcpm > + * operations that may affect the CPU (such as kexec trashing the > + * kernel text). > + * > + * It is *not* necessary to call this function if you only need to > + * serialise a pending powerdown with mcpm_cpu_power_up() or a wakeup > + * event. > + * > + * Do not call this function unless the specified CPU has already > + * called mcpm_cpu_power_down() or has committed to doing so. > + * > + * @return: > + * - zero if the CPU is in a safely parked state > + * - nonzero otherwise (e.g., timeout) > + */ > +int mcpm_cpu_power_down_finish(unsigned int cpu, unsigned int cluster); > + > +/** > * mcpm_cpu_suspend - bring the calling CPU in a suspended state > * > * @expected_residency: duration in microseconds the CPU is expected > @@ -126,6 +156,7 @@ int mcpm_cpu_powered_up(void); > struct mcpm_platform_ops { > int (*power_up)(unsigned int cpu, unsigned int cluster); > void (*power_down)(void); > + int (*power_down_finish)(unsigned int cpu, unsigned int cluster); > void (*suspend)(u64); > void (*powered_up)(void); > }; > -- > 1.7.9.5 >
On Tue, Oct 01, 2013 at 01:35:17PM -0400, Nicolas Pitre wrote: > On Tue, 1 Oct 2013, Dave Martin wrote: > > > CPU hotplug and kexec rely on smp_ops.cpu_kill(), which is supposed > > to wait for the CPU to park or power down, and perform the last > > rites (such as disabling clocks etc., where the platform doesn't do > > this automatically). > > > > kexec in particular is unsafe without performing this > > synchronisation to park secondaries. Without it, the secondaries > > might not be parked when kexec trashes the kernel. > > > > There is no generic way to do this synchronisation, so a new mcpm > > platform_ops method power_down_finish() is added by this patch. > > > > The new method is mandatory. A platform which provides no way to > > detect when CPUs are parked is likely broken. > > > > Signed-off-by: Dave Martin <Dave.Martin@arm.com> > > Reviewed-by: Nicolas Pitre <nico@linaro.org> Thanks! I can recommend kexec -- speeds up my reboots no end. I can send the MCPM patches to the patch system, but the TC2 patch probably ought to go via arm-soc when Russell has a stable branch available. Lorenzo's patch fixes something relevant but independent, so should be mergeable separately. Any concerns? Cheers ---Dave
On Tue, 1 Oct 2013, Dave Martin wrote: > On Tue, Oct 01, 2013 at 01:35:17PM -0400, Nicolas Pitre wrote: > > On Tue, 1 Oct 2013, Dave Martin wrote: > > > > > CPU hotplug and kexec rely on smp_ops.cpu_kill(), which is supposed > > > to wait for the CPU to park or power down, and perform the last > > > rites (such as disabling clocks etc., where the platform doesn't do > > > this automatically). > > > > > > kexec in particular is unsafe without performing this > > > synchronisation to park secondaries. Without it, the secondaries > > > might not be parked when kexec trashes the kernel. > > > > > > There is no generic way to do this synchronisation, so a new mcpm > > > platform_ops method power_down_finish() is added by this patch. > > > > > > The new method is mandatory. A platform which provides no way to > > > detect when CPUs are parked is likely broken. > > > > > > Signed-off-by: Dave Martin <Dave.Martin@arm.com> > > > > Reviewed-by: Nicolas Pitre <nico@linaro.org> > > Thanks! > > I can recommend kexec -- speeds up my reboots no end. > > > I can send the MCPM patches to the patch system, but the TC2 patch > probably ought to go via arm-soc when Russell has a stable branch > available. Agreed. You may ask Russell explicitly for it. Yet my patch #7842/1 upon which yours are based should go upstream before v3.12-final whereas your patches are meant for the next merge window. This should be mentioned explicitly to avoid potential confusion. > Lorenzo's patch fixes something relevant but independent, so should be > mergeable separately. Agreed. And it is on its way already. Nicolas
diff --git a/arch/arm/common/mcpm_entry.c b/arch/arm/common/mcpm_entry.c index 9902509..6c03d01 100644 --- a/arch/arm/common/mcpm_entry.c +++ b/arch/arm/common/mcpm_entry.c @@ -90,6 +90,21 @@ void mcpm_cpu_power_down(void) BUG(); } +int mcpm_cpu_power_down_finish(unsigned int cpu, unsigned int cluster) +{ + int ret; + + if (WARN_ON_ONCE(!platform_ops || !platform_ops->power_down_finish)) + return -EUNATCH; + + ret = platform_ops->power_down_finish(cpu, cluster); + if (ret) + pr_warn("%s: cpu %u, cluster %u failed to power down (%d)\n", + __func__, cpu, cluster, ret); + + return ret; +} + void mcpm_cpu_suspend(u64 expected_residency) { phys_reset_t phys_reset; diff --git a/arch/arm/common/mcpm_platsmp.c b/arch/arm/common/mcpm_platsmp.c index c0c3cd7..177251a 100644 --- a/arch/arm/common/mcpm_platsmp.c +++ b/arch/arm/common/mcpm_platsmp.c @@ -56,6 +56,15 @@ static void mcpm_secondary_init(unsigned int cpu) #ifdef CONFIG_HOTPLUG_CPU +static int mcpm_cpu_kill(unsigned int cpu) +{ + unsigned int pcpu, pcluster; + + cpu_to_pcpu(cpu, &pcpu, &pcluster); + + return !mcpm_cpu_power_down_finish(pcpu, pcluster); +} + static int mcpm_cpu_disable(unsigned int cpu) { /* @@ -82,6 +91,7 @@ static struct smp_operations __initdata mcpm_smp_ops = { .smp_boot_secondary = mcpm_boot_secondary, .smp_secondary_init = mcpm_secondary_init, #ifdef CONFIG_HOTPLUG_CPU + .cpu_kill = mcpm_cpu_kill, .cpu_disable = mcpm_cpu_disable, .cpu_die = mcpm_cpu_die, #endif diff --git a/arch/arm/include/asm/mcpm.h b/arch/arm/include/asm/mcpm.h index fc82a88..1cf2601 100644 --- a/arch/arm/include/asm/mcpm.h +++ b/arch/arm/include/asm/mcpm.h @@ -81,10 +81,40 @@ int mcpm_cpu_power_up(unsigned int cpu, unsigned int cluster); * * This will return if mcpm_platform_register() has not been called * previously in which case the caller should take appropriate action. + * + * On success, the CPU is not guaranteed to be truly halted until + * mcpm_cpu_power_down_finish() subsequently returns non-zero for the + * specified cpu. Until then, other CPUs should make sure they do not + * trash memory the target CPU might be executing/accessing. */ void mcpm_cpu_power_down(void); /** + * mcpm_cpu_power_down_finish - wait for a specified CPU to halt, and + * make sure it is powered off + * + * @cpu: CPU number within given cluster + * @cluster: cluster number for the CPU + * + * Call this function to ensure that a pending powerdown has taken + * effect and the CPU is safely parked before performing non-mcpm + * operations that may affect the CPU (such as kexec trashing the + * kernel text). + * + * It is *not* necessary to call this function if you only need to + * serialise a pending powerdown with mcpm_cpu_power_up() or a wakeup + * event. + * + * Do not call this function unless the specified CPU has already + * called mcpm_cpu_power_down() or has committed to doing so. + * + * @return: + * - zero if the CPU is in a safely parked state + * - nonzero otherwise (e.g., timeout) + */ +int mcpm_cpu_power_down_finish(unsigned int cpu, unsigned int cluster); + +/** * mcpm_cpu_suspend - bring the calling CPU in a suspended state * * @expected_residency: duration in microseconds the CPU is expected @@ -126,6 +156,7 @@ int mcpm_cpu_powered_up(void); struct mcpm_platform_ops { int (*power_up)(unsigned int cpu, unsigned int cluster); void (*power_down)(void); + int (*power_down_finish)(unsigned int cpu, unsigned int cluster); void (*suspend)(u64); void (*powered_up)(void); };
CPU hotplug and kexec rely on smp_ops.cpu_kill(), which is supposed to wait for the CPU to park or power down, and perform the last rites (such as disabling clocks etc., where the platform doesn't do this automatically). kexec in particular is unsafe without performing this synchronisation to park secondaries. Without it, the secondaries might not be parked when kexec trashes the kernel. There is no generic way to do this synchronisation, so a new mcpm platform_ops method power_down_finish() is added by this patch. The new method is mandatory. A platform which provides no way to detect when CPUs are parked is likely broken. Signed-off-by: Dave Martin <Dave.Martin@arm.com> --- arch/arm/common/mcpm_entry.c | 15 +++++++++++++++ arch/arm/common/mcpm_platsmp.c | 10 ++++++++++ arch/arm/include/asm/mcpm.h | 31 +++++++++++++++++++++++++++++++ 3 files changed, 56 insertions(+)