PM / QoS: Fix device resume latency PM QoS

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>
Tested-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Alex Shi <alex.shi@linaro.org>
Cc: All applicable <stable@vger.kernel.org>

8 files changed, 63 insertions, 35 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power
index 676fdf5f2a99..5cbb6f038615 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_governor.c b/drivers/base/power/domain_governor.c
index 281f949c5ffe..51751cc8c9e6 100644
--- a/drivers/base/power/domain_governor.c
+++ b/drivers/base/power/domain_governor.c
@@ -14,23 +14,20 @@
 static int dev_update_qos_constraint(struct device *dev, void *data)
 {
         s64 *constraint_ns_p = data;
-        s32 constraint_ns = -1;
+        s64 constraint_ns = -1;
 
         if (dev->power.subsys_data && dev->power.subsys_data->domain_data)
                 constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns;
 
-        if (constraint_ns < 0) {
+        if (constraint_ns < 0)
                 constraint_ns = dev_pm_qos_read_value(dev);
-                constraint_ns *= NSEC_PER_USEC;
-        }
-        if (constraint_ns == 0)
+
+        if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
                 return 0;
 
-        /*
-         * constraint_ns cannot be negative here, because the device has been
-         * suspended.
-         */
-        if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0)
+        constraint_ns *= NSEC_PER_USEC;
+
+        if (constraint_ns < *constraint_ns_p || *constraint_ns_p < 0)
                 *constraint_ns_p = constraint_ns;
 
         return 0;
@@ -63,10 +60,14 @@ static bool default_suspend_ok(struct device *dev)
 
         spin_unlock_irqrestore(&dev->power.lock, flags);
 
-        if (constraint_ns < 0)
+        if (constraint_ns == 0)
                 return false;
 
-        constraint_ns *= NSEC_PER_USEC;
+        if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
+                constraint_ns = -1;
+        else
+                constraint_ns *= NSEC_PER_USEC;
+
         /*
          * We can walk the children without any additional locking, because
          * they all have been suspended at this point and their
@@ -76,14 +77,19 @@ static bool default_suspend_ok(struct device *dev)
                 device_for_each_child(dev, &constraint_ns,
                                       dev_update_qos_constraint);
 
-        if (constraint_ns > 0) {
-                constraint_ns -= td->suspend_latency_ns +
-                                td->resume_latency_ns;
-                if (constraint_ns == 0)
-                        return false;
+        if (constraint_ns < 0) {
+                /* The children have no constraints. */
+                td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+                td->cached_suspend_ok = true;
+        } else {
+                constraint_ns -= td->suspend_latency_ns + td->resume_latency_ns;
+                if (constraint_ns > 0) {
+                        td->effective_constraint_ns = constraint_ns;
+                        td->cached_suspend_ok = true;
+                } else {
+                        td->effective_constraint_ns = 0;
+                }
         }
-        td->effective_constraint_ns = constraint_ns;
-        td->cached_suspend_ok = constraint_ns >= 0;
 
         /*
          * The children have been suspended already, so we don't need to take
@@ -145,13 +151,14 @@ static bool __default_power_down_ok(struct dev_pm_domain *pd,
                 td = &to_gpd_data(pdd)->td;
                 constraint_ns = td->effective_constraint_ns;
                 /* default_suspend_ok() need not be called before us. */
-                if (constraint_ns < 0) {
+                if (constraint_ns < 0)
                         constraint_ns = dev_pm_qos_read_value(pdd->dev);
-                        constraint_ns *= NSEC_PER_USEC;
-                }
-                if (constraint_ns == 0)
+
+                if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
                         continue;
 
+                constraint_ns *= NSEC_PER_USEC;
+
                 /*
                  * constraint_ns cannot be negative here, because the device has
                  * been suspended.
diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
index 277d43a83f53..7d29286d9313 100644
--- a/drivers/base/power/qos.c
+++ b/drivers/base/power/qos.c
@@ -189,7 +189,7 @@ 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 156ab57bca77..632077f05c57 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 032b55909145..6737a8c9e8c6 100644
--- a/include/linux/pm_qos.h
+++ b/include/linux/pm_qos.h
@@ -27,16 +27,17 @@ 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_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_NO_CONSTRAINT     PM_QOS_LATENCY_ANY
 #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)
 #define PM_QOS_FLAG_REMOTE_WAKEUP       (1 << 1)