PM / QoS: Fix device resume latency framework

The special value of 0 for device resume latency PM QoS means
"no restriction", but there are two problems with that.

First, device resume latency PM QoS requests with 0 as the
value are always put in front of requests with positive
values in the priority lists used internally by the PM QoS
framework, causing 0 to be chosen as an effective constraint
value.  However, that 0 is then interpreted as "no restriction"
effectively overriding the other requests with specific
restrictions which is incorrect.

Second, the users of device resume latency PM QoS have no
way to specify that *any* resume latency at all should be
avoided, which is an artificial limitation in general.

To address these issues, modify device resume latency PM QoS to
use S32_MAX as the "no constraint" value and 0 as the "no
latency at all" one and rework its users (the cpuidle menu
governor, the genpd QoS governor and the runtime PM framework)
to follow these changes.

Also add a special "n/a" value to the corresponding user space I/F
to allow user space to indicate that it cannot accept any resume
latencies at all for the given device.

Fixes: 85dc0b8a4019 (PM / QoS: Make it possible to expose PM QoS latency constraints)
Link: https://bugzilla.kernel.org/show_bug.cgi?id=197323
Reported-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Ramesh Thomas <ramesh.thomas@intel.com>

9 files changed, 68 insertions, 43 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power
index f4b24c327665..80a00f7b6667 100644
--- a/Documentation/ABI/testing/sysfs-devices-power
+++ b/Documentation/ABI/testing/sysfs-devices-power
@@ -211,7 +211,9 @@ Description:
                 device, after it has been suspended at run time, from a resume
                 request to the moment the device will be ready to process I/O,
                 in microseconds.  If it is equal to 0, however, this means that
-                the PM QoS resume latency may be arbitrary.
+                the PM QoS resume latency may be arbitrary and the special value
+                "n/a" means that user space cannot accept any resume latency at
+                all for the given device.
 
                 Not all drivers support this attribute.  If it isn't supported,
                 it is not present.
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 321cd7b4d817..227bac5f1191 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -377,7 +377,8 @@ int register_cpu(struct cpu *cpu, int num)
 
         per_cpu(cpu_sys_devices, num) = &cpu->dev;
         register_cpu_under_node(num, cpu_to_node(num));
-        dev_pm_qos_expose_latency_limit(&cpu->dev, 0);
+        dev_pm_qos_expose_latency_limit(&cpu->dev,
+                                        PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
 
         return 0;
 }
diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index 679c79545e42..24e39ce27bd8 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -1326,7 +1326,7 @@ static struct generic_pm_domain_data *genpd_alloc_dev_data(struct device *dev,
 
         gpd_data->base.dev = dev;
         gpd_data->td.constraint_changed = true;
-        gpd_data->td.effective_constraint_ns = 0;
+        gpd_data->td.effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
         gpd_data->nb.notifier_call = genpd_dev_pm_qos_notifier;
 
         spin_lock_irq(&dev->power.lock);
diff --git a/drivers/base/power/domain_governor.c b/drivers/base/power/domain_governor.c
index e4cca8adab32..99896fbf18e4 100644
--- a/drivers/base/power/domain_governor.c
+++ b/drivers/base/power/domain_governor.c
@@ -33,15 +33,10 @@ static int dev_update_qos_constraint(struct device *dev, void *data)
                  * known at this point anyway).
                  */
                 constraint_ns = dev_pm_qos_read_value(dev);
-                if (constraint_ns > 0)
-                        constraint_ns *= NSEC_PER_USEC;
+                constraint_ns *= NSEC_PER_USEC;
         }
 
-        /* 0 means "no constraint" */
-        if (constraint_ns == 0)
-                return 0;
-
-        if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0)
+        if (constraint_ns < *constraint_ns_p)
                 *constraint_ns_p = constraint_ns;
 
         return 0;
@@ -69,12 +64,12 @@ static bool default_suspend_ok(struct device *dev)
         }
         td->constraint_changed = false;
         td->cached_suspend_ok = false;
-        td->effective_constraint_ns = -1;
+        td->effective_constraint_ns = 0;
         constraint_ns = __dev_pm_qos_read_value(dev);
 
         spin_unlock_irqrestore(&dev->power.lock, flags);
 
-        if (constraint_ns < 0)
+        if (constraint_ns == 0)
                 return false;
 
         constraint_ns *= NSEC_PER_USEC;
@@ -87,25 +82,25 @@ static bool default_suspend_ok(struct device *dev)
                 device_for_each_child(dev, &constraint_ns,
                                       dev_update_qos_constraint);
 
-        if (constraint_ns == 0) {
+        if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS) {
                 /* "No restriction", so the device is allowed to suspend. */
-                td->effective_constraint_ns = 0;
+                td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
                 td->cached_suspend_ok = true;
-        } else if (constraint_ns < 0) {
+        } else if (constraint_ns == 0) {
                 /*
                  * This triggers if one of the children that don't belong to a
-                 * domain has a negative PM QoS constraint and it's better not
-                 * to suspend then.  effective_constraint_ns is negative already
-                 * and cached_suspend_ok is false, so bail out.
+                 * domain has a zero PM QoS constraint and it's better not to
+                 * suspend then.  effective_constraint_ns is zero already and
+                 * cached_suspend_ok is false, so bail out.
                  */
                 return false;
         } else {
                 constraint_ns -= td->suspend_latency_ns +
                                 td->resume_latency_ns;
                 /*
-                 * effective_constraint_ns is negative already and
-                 * cached_suspend_ok is false, so if the computed value is not
-                 * positive, return right away.
+                 * effective_constraint_ns is zero already and cached_suspend_ok
+                 * is false, so if the computed value is not positive, return
+                 * right away.
                  */
                 if (constraint_ns <= 0)
                         return false;
@@ -174,13 +169,10 @@ static bool __default_power_down_ok(struct dev_pm_domain *pd,
                 td = &to_gpd_data(pdd)->td;
                 constraint_ns = td->effective_constraint_ns;
                 /*
-                 * Negative values mean "no suspend at all" and this runs only
-                 * when all devices in the domain are suspended, so it must be
-                 * 0 at least.
-                 *
-                 * 0 means "no constraint"
+                 * Zero means "no suspend at all" and this runs only when all
+                 * devices in the domain are suspended, so it must be positive.
                  */
-                if (constraint_ns == 0)
+                if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS)
                         continue;
 
                 if (constraint_ns <= off_on_time_ns)
diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
index 277d43a83f53..3382542b39b7 100644
--- a/drivers/base/power/qos.c
+++ b/drivers/base/power/qos.c
@@ -139,6 +139,9 @@ static int apply_constraint(struct dev_pm_qos_request *req,
 
         switch(req->type) {
         case DEV_PM_QOS_RESUME_LATENCY:
+                if (WARN_ON(action != PM_QOS_REMOVE_REQ && value < 0))
+                        value = 0;
+
                 ret = pm_qos_update_target(&qos->resume_latency,
                                            &req->data.pnode, action, value);
                 break;
@@ -189,7 +192,7 @@ static int dev_pm_qos_constraints_allocate(struct device *dev)
         plist_head_init(&c->list);
         c->target_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;
         c->default_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;
-        c->no_constraint_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;
+        c->no_constraint_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
         c->type = PM_QOS_MIN;
         c->notifiers = n;
 
diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 7bcf80fa9ada..13e015905543 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -253,7 +253,7 @@ static int rpm_check_suspend_allowed(struct device *dev)
             || (dev->power.request_pending
                         && dev->power.request == RPM_REQ_RESUME))
                 retval = -EAGAIN;
-        else if (__dev_pm_qos_read_value(dev) < 0)
+        else if (__dev_pm_qos_read_value(dev) == 0)
                 retval = -EPERM;
         else if (dev->power.runtime_status == RPM_SUSPENDED)
                 retval = 1;
diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
index 29bf28fef136..e153e28b1857 100644
--- a/drivers/base/power/sysfs.c
+++ b/drivers/base/power/sysfs.c
@@ -218,7 +218,14 @@ static ssize_t pm_qos_resume_latency_show(struct device *dev,
                                           struct device_attribute *attr,
                                           char *buf)
 {
-        return sprintf(buf, "%d\n", dev_pm_qos_requested_resume_latency(dev));
+        s32 value = dev_pm_qos_requested_resume_latency(dev);
+
+        if (value == 0)
+                return sprintf(buf, "n/a\n");
+        else if (value == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
+                value = 0;
+
+        return sprintf(buf, "%d\n", value);
 }
 
 static ssize_t pm_qos_resume_latency_store(struct device *dev,
@@ -228,11 +235,21 @@ static ssize_t pm_qos_resume_latency_store(struct device *dev,
         s32 value;
         int ret;
 
-        if (kstrtos32(buf, 0, &value))
-                return -EINVAL;
+        if (!kstrtos32(buf, 0, &value)) {
+                /*
+                 * Prevent users from writing negative or "no constraint" values
+                 * directly.
+                 */
+                if (value < 0 || value == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
+                        return -EINVAL;
 
-        if (value < 0)
+                if (value == 0)
+                        value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+        } else if (!strcmp(buf, "n/a") || !strcmp(buf, "n/a\n")) {
+                value = 0;
+        } else {
                 return -EINVAL;
+        }
 
         ret = dev_pm_qos_update_request(dev->power.qos->resume_latency_req,
                                         value);
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 48eaf2879228..aa390404e85f 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -298,8 +298,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
                 data->needs_update = 0;
         }
 
-        /* resume_latency is 0 means no restriction */
-        if (resume_latency && resume_latency < latency_req)
+        if (resume_latency < latency_req &&
+            resume_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
                 latency_req = resume_latency;
 
         /* Special case when user has set very strict latency requirement */
diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
index 51f0d7e0b15f..2a3b36da61b1 100644
--- a/include/linux/pm_qos.h
+++ b/include/linux/pm_qos.h
@@ -27,16 +27,19 @@ enum pm_qos_flags_status {
         PM_QOS_FLAGS_ALL,
 };
 
-#define PM_QOS_DEFAULT_VALUE -1
+#define PM_QOS_DEFAULT_VALUE    (-1)
+#define PM_QOS_LATENCY_ANY      S32_MAX
+#define PM_QOS_LATENCY_ANY_NS   ((s64)PM_QOS_LATENCY_ANY * NSEC_PER_USEC)
 
 #define PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE        (2000 * USEC_PER_SEC)
 #define PM_QOS_NETWORK_LAT_DEFAULT_VALUE        (2000 * USEC_PER_SEC)
 #define PM_QOS_NETWORK_THROUGHPUT_DEFAULT_VALUE 0
 #define PM_QOS_MEMORY_BANDWIDTH_DEFAULT_VALUE   0
-#define PM_QOS_RESUME_LATENCY_DEFAULT_VALUE     0
+#define PM_QOS_RESUME_LATENCY_DEFAULT_VALUE     PM_QOS_LATENCY_ANY
+#define PM_QOS_RESUME_LATENCY_NO_CONSTRAINT     PM_QOS_LATENCY_ANY
+#define PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS  PM_QOS_LATENCY_ANY_NS
 #define PM_QOS_LATENCY_TOLERANCE_DEFAULT_VALUE  0
 #define PM_QOS_LATENCY_TOLERANCE_NO_CONSTRAINT  (-1)
-#define PM_QOS_LATENCY_ANY                      ((s32)(~(__u32)0 >> 1))
 
 #define PM_QOS_FLAG_NO_POWER_OFF        (1 << 0)
 
@@ -173,7 +176,8 @@ static inline s32 dev_pm_qos_requested_flags(struct device *dev)
 static inline s32 dev_pm_qos_raw_read_value(struct device *dev)
 {
         return IS_ERR_OR_NULL(dev->power.qos) ?
-                0 : pm_qos_read_value(&dev->power.qos->resume_latency);
+                PM_QOS_RESUME_LATENCY_NO_CONSTRAINT :
+                pm_qos_read_value(&dev->power.qos->resume_latency);
 }
 #else
 static inline enum pm_qos_flags_status __dev_pm_qos_flags(struct device *dev,
@@ -183,9 +187,9 @@ static inline enum pm_qos_flags_status dev_pm_qos_flags(struct device *dev,
                                                         s32 mask)
                         { return PM_QOS_FLAGS_UNDEFINED; }
 static inline s32 __dev_pm_qos_read_value(struct device *dev)
-                        { return 0; }
+                        { return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT; }
 static inline s32 dev_pm_qos_read_value(struct device *dev)
-                        { return 0; }
+                        { return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT; }
 static inline int dev_pm_qos_add_request(struct device *dev,
                                          struct dev_pm_qos_request *req,
                                          enum dev_pm_qos_req_type type,
@@ -231,9 +235,15 @@ static inline int dev_pm_qos_expose_latency_tolerance(struct device *dev)
                         { return 0; }
 static inline void dev_pm_qos_hide_latency_tolerance(struct device *dev) {}
 
-static inline s32 dev_pm_qos_requested_resume_latency(struct device *dev) { return 0; }
+static inline s32 dev_pm_qos_requested_resume_latency(struct device *dev)
+{
+        return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+}
 static inline s32 dev_pm_qos_requested_flags(struct device *dev) { return 0; }
-static inline s32 dev_pm_qos_raw_read_value(struct device *dev) { return 0; }
+static inline s32 dev_pm_qos_raw_read_value(struct device *dev)
+{
+        return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+}
 #endif
 
 #endif