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SubjectRe: [PATCH v10 24/27] drivers: firmware: psci: Support CPU hotplug for the hierarchical model
On Thu, Nov 29, 2018 at 06:46:57PM +0100, Ulf Hansson wrote:
> When the hierarchical CPU topology is used and when a CPU has been put
> offline (hotplug), that same CPU prevents its PM domain and thus also
> potential master PM domains, from being powered off. This is because genpd
> observes the CPU's struct device to remain being active from a runtime PM
> point of view.
>
> To deal with this, let's decrease the runtime PM usage count by calling
> pm_runtime_put_sync_suspend() of the CPU's struct device when putting it
> offline. Consequentially, we must then increase the runtime PM usage for
> the CPU, while putting it online again.
>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
>
> Changes in v10:
> - Make it work when the hierarchical CPU topology is used, which may be
> used both for OSI and PC mode.
> - Rework the code to prevent "BUG: sleeping function called from
> invalid context".
> ---
> drivers/firmware/psci/psci.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> index b03bccce0a5d..f62c4963eb62 100644
> --- a/drivers/firmware/psci/psci.c
> +++ b/drivers/firmware/psci/psci.c
> @@ -15,6 +15,7 @@
>
> #include <linux/acpi.h>
> #include <linux/arm-smccc.h>
> +#include <linux/cpu.h>
> #include <linux/cpuidle.h>
> #include <linux/errno.h>
> #include <linux/linkage.h>
> @@ -199,9 +200,20 @@ static int psci_cpu_suspend(u32 state, unsigned long entry_point)
>
> static int psci_cpu_off(u32 state)
> {
> + struct device *dev;
> int err;
> u32 fn;
>
> + /*
> + * When the hierarchical CPU topology is used, decrease the runtime PM
> + * usage count for the current CPU, as to allow other parts in the
> + * topology to enter low power states.
> + */
> + if (psci_dt_topology) {
> + dev = get_cpu_device(smp_processor_id());
> + pm_runtime_put_sync_suspend(dev);
> + }
> +
> fn = psci_function_id[PSCI_FN_CPU_OFF];
> err = invoke_psci_fn(fn, state, 0, 0);
> return psci_to_linux_errno(err);
> @@ -209,6 +221,7 @@ static int psci_cpu_off(u32 state)
>
> static int psci_cpu_on(unsigned long cpuid, unsigned long entry_point)
> {
> + struct device *dev;
> int err;
> u32 fn;
>
> @@ -216,6 +229,13 @@ static int psci_cpu_on(unsigned long cpuid, unsigned long entry_point)
> err = invoke_psci_fn(fn, cpuid, entry_point, 0);
> /* Clear the domain state to start fresh. */
> psci_set_domain_state(0);
> +
> + /* Increase runtime PM usage count if the hierarchical CPU toplogy. */
> + if (!err && psci_dt_topology) {
> + dev = get_cpu_device(cpuid);

I do not like adding this code in the cpu_{on/off} method themselves, I will
have a look at the patchset as whole to see how we can restructure it.

More to the point, using cpuid as a logical cpu id is wrong, it is a
physical id that you should convert to a logical id through
get_logical_index().

Lorenzo

> + pm_runtime_get_sync(dev);
> + }
> +
> return psci_to_linux_errno(err);
> }
>
> --
> 2.17.1
>

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