On Thu, 3 Jul 2014, Abhilash Kesavan wrote:
> Hi Nicolas,
>
> On Thu, Jul 3, 2014 at 9:15 PM, Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> wrote:
> > On Thu, 3 Jul 2014, Abhilash Kesavan wrote:
> >
> >> On Thu, Jul 3, 2014 at 6:59 PM, Nicolas Pitre <nicolas.pitre@xxxxxxxxxx> wrote:
> >> > Please, let's avoid going that route. There is no such special handling
> >> > needed if the API is sufficient. And the provided API allows you to
> >> > suspend a CPU or shut it down. It shouldn't matter at that level if
> >> > this is due to a cluster switch or a hotplug event. Do you really need
> >> > something else?
> >> No, just one local flag for suspend should be enough for me. Will remove these.
> >
> > [...]
> >
> >> Changes in v5:
> >> - Removed the MCPM flags and just used a local flag to
> >> indicate that we are suspending.
> >
> > [...]
> >
> >> -static void exynos_power_down(void)
> >> +static void exynos_mcpm_power_down(u64 residency)
> >> {
> >> unsigned int mpidr, cpu, cluster;
> >> bool last_man = false, skip_wfi = false;
> >> @@ -150,7 +153,12 @@ static void exynos_power_down(void)
> >> BUG_ON(__mcpm_cluster_state(cluster) != CLUSTER_UP);
> >> cpu_use_count[cpu][cluster]--;
> >> if (cpu_use_count[cpu][cluster] == 0) {
> >> - exynos_cpu_power_down(cpunr);
> >> + /*
> >> + * Bypass power down for CPU0 during suspend. This is being
> >> + * taken care by the SYS_PWR_CFG bit in CORE0_SYS_PWR_REG.
> >> + */
> >> + if ((cpunr != 0) || (residency != S5P_CHECK_SLEEP))
> >> + exynos_cpu_power_down(cpunr);
> >>
> >> if (exynos_cluster_unused(cluster)) {
> >> exynos_cluster_power_down(cluster);
> >> @@ -209,6 +217,11 @@ static void exynos_power_down(void)
> >> /* Not dead at this point? Let our caller cope. */
> >> }
> >>
> >> +static void exynos_power_down(void)
> >> +{
> >> + exynos_mcpm_power_down(0);
> >> +}
> >
> > [...]
> >
> >> +static int notrace exynos_mcpm_cpu_suspend(unsigned long arg)
> >> +{
> >> + /* MCPM works with HW CPU identifiers */
> >> + unsigned int mpidr = read_cpuid_mpidr();
> >> + unsigned int cluster = MPIDR_AFFINITY_LEVEL(mpidr, 1);
> >> + unsigned int cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);
> >> +
> >> + __raw_writel(0x0, sysram_base_addr + EXYNOS5420_CPU_STATE);
> >> +
> >> + mcpm_set_entry_vector(cpu, cluster, exynos_cpu_resume);
> >> +
> >> + /*
> >> + * Pass S5P_CHECK_SLEEP flag to the MCPM back-end to indicate that
> >> + * we are suspending the system and need to skip CPU0 power down.
> >> + */
> >> + mcpm_cpu_suspend(S5P_CHECK_SLEEP);
> >
> > NAK.
> >
> > When I say "local flag with local meaning", I don't want you to smuggle
> > that flag through a public interface either. I find it rather inelegant
> > to have the notion of special handling for CPU0 being spread around like
> > that.
> >
> > If CPU0 is special, then it should be dealth with in one place only,
> > ideally in the MCPM backend, so the rest of the kernel doesn't have to
> > care.
> >
> > Again, here's what I mean:
> >
> > static void exynos_mcpm_down_handler(int flags)
> > {
> > [...]
> > if ((cpunr != 0) || !(flags & SKIP_CPU_POWERDOWN_IF_CPU0))
> > exynos_cpu_power_down(cpunr);
> > [...]
> > }
> >
> > static void exynos_mcpm_power_down()
> > {
> > exynos_mcpm_down_handler(0);
> > }
> >
> > static void exynos_mcpm_suspend(u64 residency)
> > {
> > /*
> > * Theresidency argument is ignored for now.
> > * However, in the CPU suspend case, we bypass power down for
> > * CPU0 as this is being taken care by the SYS_PWR_CFG bit in
> > * CORE0_SYS_PWR_REG.
> > */
> > exynos_mcpm_down_handler(SKIP_CPU_POWERDOWN_IF_CPU0);
> > }
> >
> > And SKIP_CPU_POWERDOWN_IF_CPU0 is defined in and visible to
> > mcpm-exynos.c only.
> Sorry if I am being dense, but the exynos_mcpm_suspend function would
> get called from both the bL cpuidle driver as well the exynos pm code.
What is that exynos pm code actually doing?
> We want to skip CPU0 only in case of the S2R case i.e. the pm code and
> keep the CPU0 power down code for all other cases including CPUIdle.
OK. If so I missed that somehow (hint hint).
> If I call exynos_mcpm_down_handler with the flag in
> exynos_mcpm_suspend(), CPUIdle will also skip CPU0 isn't it ?
As it is, yes. You could logically use an infinite residency time
(something like U64_MAX) to distinguish S2RAM from other types of
suspend.
Yet, why is this SYS_PWR_CFG bit set outside of MCPM? Couldn't the MCPM
backend handle it directly instead of expecting some other entity to do
it?
Nicolas
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