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Subject[PATCH 3/9] PM / Domains: Do not take parent locks to modify subdomain counters
Date
From: Rafael J. Wysocki <rjw@sisk.pl>

After the subdomain counter in struct generic_pm_domain has been
changed into an atomic_t field, it is possible to modify
pm_genpd_poweron() and pm_genpd_poweroff() so that they don't take
the parents locks. This requires pm_genpd_poweron() to increment
the parent's subdomain counter before calling itself recursively
for the parent and to decrement it if an error is to be returned.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
drivers/base/power/domain.c | 70 +++++++++++++++++++-------------------------
1 file changed, 31 insertions(+), 39 deletions(-)

Index: linux-2.6/drivers/base/power/domain.c
===================================================================
--- linux-2.6.orig/drivers/base/power/domain.c
+++ linux-2.6/drivers/base/power/domain.c
@@ -93,12 +93,7 @@ int pm_genpd_poweron(struct generic_pm_d
int ret = 0;

start:
- if (parent) {
- genpd_acquire_lock(parent);
- mutex_lock_nested(&genpd->lock, SINGLE_DEPTH_NESTING);
- } else {
- mutex_lock(&genpd->lock);
- }
+ mutex_lock(&genpd->lock);

if (genpd->status == GPD_STATE_ACTIVE
|| (genpd->prepared_count > 0 && genpd->suspend_power_off))
@@ -109,31 +104,33 @@ int pm_genpd_poweron(struct generic_pm_d
goto out;
}

- if (parent && parent->status != GPD_STATE_ACTIVE) {
+ if (parent) {
+ genpd_sd_counter_inc(parent);
+
mutex_unlock(&genpd->lock);
- genpd_release_lock(parent);

ret = pm_genpd_poweron(parent);
- if (ret)
+ if (ret) {
+ genpd_sd_counter_dec(parent);
return ret;
+ }

+ parent = NULL;
goto start;
}

- if (genpd->power_on) {
+ if (genpd->power_on)
ret = genpd->power_on(genpd);
- if (ret)
- goto out;
- }

- genpd_set_active(genpd);
- if (parent)
- genpd_sd_counter_inc(parent);
+ if (ret) {
+ if (genpd->parent)
+ genpd_sd_counter_dec(genpd->parent);
+ } else {
+ genpd_set_active(genpd);
+ }

out:
mutex_unlock(&genpd->lock);
- if (parent)
- genpd_release_lock(parent);

return ret;
}
@@ -293,7 +290,8 @@ static int pm_genpd_poweroff(struct gene
genpd->poweroff_task = current;

list_for_each_entry_reverse(dle, &genpd->dev_list, node) {
- ret = __pm_genpd_save_device(dle, genpd);
+ ret = atomic_read(&genpd->sd_count) == 0 ?
+ __pm_genpd_save_device(dle, genpd) : -EBUSY;
if (ret) {
genpd_set_active(genpd);
goto out;
@@ -308,38 +306,32 @@ static int pm_genpd_poweroff(struct gene
}
}

- parent = genpd->parent;
- if (parent) {
- mutex_unlock(&genpd->lock);
-
- genpd_acquire_lock(parent);
- mutex_lock_nested(&genpd->lock, SINGLE_DEPTH_NESTING);
-
- if (genpd_abort_poweroff(genpd)) {
- genpd_release_lock(parent);
+ if (genpd->power_off) {
+ if (atomic_read(&genpd->sd_count) > 0) {
+ ret = -EBUSY;
goto out;
}
- }

- if (genpd->power_off) {
+ /*
+ * If sd_count > 0 at this point, one of the children hasn't
+ * managed to call pm_genpd_poweron() for the parent yet after
+ * incrementing it. In that case pm_genpd_poweron() will wait
+ * for us to drop the lock, so we can call .power_off() and let
+ * the pm_genpd_poweron() restore power for us (this shouldn't
+ * happen very often).
+ */
ret = genpd->power_off(genpd);
if (ret == -EBUSY) {
genpd_set_active(genpd);
- if (parent)
- genpd_release_lock(parent);
-
goto out;
}
}

genpd->status = GPD_STATE_POWER_OFF;

- if (parent) {
- if (genpd_sd_counter_dec(parent))
- genpd_queue_power_off_work(parent);
-
- genpd_release_lock(parent);
- }
+ parent = genpd->parent;
+ if (parent && genpd_sd_counter_dec(parent))
+ genpd_queue_power_off_work(parent);

out:
genpd->poweroff_task = NULL;


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