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SubjectRe: [PATCH RFC 1/2] PM: domains: Add GENPD_FLAG_RT_SAFE for PREEMPT_RT
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On 16/12/2022 15:58, Krzysztof Kozlowski wrote:
> Realtime kernels with PREEMPT_RT must use raw_spinlock_t, so add a flag
> allowing a power domain provider to indicate it is RT safe. The flag is
> supposed to be used with existing GENPD_FLAG_IRQ_SAFE.
>
> Cc: Adrien Thierry <athierry@redhat.com>
> Cc: Brian Masney <bmasney@redhat.com>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
>
> ---
>
> Independently from Adrien, I encountered the same problem around genpd
> when using PREEMPT_RT kernel.
>
> Previous patch by Adrien:
> https://lore.kernel.org/all/20220615203605.1068453-1-athierry@redhat.com/
> ---
> drivers/base/power/domain.c | 51 +++++++++++++++++++++++++++++++++++--
> include/linux/pm_domain.h | 13 ++++++++++
> 2 files changed, 62 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index a539d6bc6fe0..478862ae478a 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -119,6 +119,48 @@ static const struct genpd_lock_ops genpd_spin_ops = {
> .unlock = genpd_unlock_spin,
> };
>
> +static void genpd_lock_rawspin(struct generic_pm_domain *genpd)
> + __acquires(&genpd->rslock)
> +{
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave(&genpd->rslock, flags);
> + genpd->rlock_flags = flags;
> +}
> +
> +static void genpd_lock_nested_rawspin(struct generic_pm_domain *genpd,
> + int depth)
> + __acquires(&genpd->rslock)
> +{
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave_nested(&genpd->rslock, flags, depth);
> + genpd->rlock_flags = flags;
> +}
> +
> +static int genpd_lock_interruptible_rawspin(struct generic_pm_domain *genpd)
> + __acquires(&genpd->rslock)
> +{
> + unsigned long flags;
> +
> + raw_spin_lock_irqsave(&genpd->rslock, flags);
> + genpd->rlock_flags = flags;
> + return 0;
> +}
> +
> +static void genpd_unlock_rawspin(struct generic_pm_domain *genpd)
> + __releases(&genpd->rslock)
> +{
> + raw_spin_unlock_irqrestore(&genpd->rslock, genpd->rlock_flags);
> +}
> +
> +static const struct genpd_lock_ops genpd_rawspin_ops = {
> + .lock = genpd_lock_rawspin,
> + .lock_nested = genpd_lock_nested_rawspin,
> + .lock_interruptible = genpd_lock_interruptible_rawspin,
> + .unlock = genpd_unlock_rawspin,
> +};
> +
> #define genpd_lock(p) p->lock_ops->lock(p)
> #define genpd_lock_nested(p, d) p->lock_ops->lock_nested(p, d)
> #define genpd_lock_interruptible(p) p->lock_ops->lock_interruptible(p)
> @@ -2048,8 +2090,13 @@ static void genpd_free_data(struct generic_pm_domain *genpd)
> static void genpd_lock_init(struct generic_pm_domain *genpd)
> {
> if (genpd->flags & GENPD_FLAG_IRQ_SAFE) {
> - spin_lock_init(&genpd->slock);
> - genpd->lock_ops = &genpd_spin_ops;
> + if (genpd->flags & GENPD_FLAG_RT_SAFE) {
> + raw_spin_lock_init(&genpd->rslock);
> + genpd->lock_ops = &genpd_rawspin_ops;
> + } else {
> + spin_lock_init(&genpd->slock);
> + genpd->lock_ops = &genpd_spin_ops;
> + }
> } else {
> mutex_init(&genpd->mlock);
> genpd->lock_ops = &genpd_mtx_ops;
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index c6cda024ff99..6b0f9de2be1c 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -61,6 +61,14 @@
> * GENPD_FLAG_MIN_RESIDENCY: Enable the genpd governor to consider its
> * components' next wakeup when determining the
> * optimal idle state.
> + *
> + * GENPD_FLAG_RT_SAFE: When used with GENPD_FLAG_IRQ_SAFE, this informs
> + * genpd that its backend callbacks, ->power_on|off(),
> + * do not use other spinlocks. They might use
> + * raw_spinlocks or other pre-emption-disable
> + * methods, all of which are PREEMPT_RT safe. Note
> + * that, a genpd having this flag set, requires its
> + * masterdomains to also have it set.

Now I see I might be missing such check in genpd_add_subdomain().

Best regards,
Krzysztof

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