[PATCH RFC 04/10] PM / devfreq: Add new target_freq attribute flag for governors

From: Sibi Sankar <[email protected]>

The target_freq sysfs attribute exposes a governor's predicted next
target frequency. Not every devfreq governor has a meaningful value
to report there; some merely observe an externally-driven device.

Add a DEVFREQ_GOV_ATTR_TARGET_FREQ attribute flag that governors with
a meaningful target frequency must opt in to. Gate the existing
target_freq sysfs read on the flag and return -EINVAL when the active
governor does not advertise it.

Tag all in-tree governors so visible behaviour stays unchanged for
in-tree users. Out-of-tree governors that drive frequency updates
and want to keep target_freq readable need to set the new flag.

Signed-off-by: Sibi Sankar <[email protected]>
Co-developed-by: Pragnesh Papaniya <[email protected]>
Signed-off-by: Pragnesh Papaniya <[email protected]>
---
 Documentation/ABI/testing/sysfs-class-devfreq | 8 ++++++++
 drivers/devfreq/devfreq.c                     | 6 ++++++
 drivers/devfreq/governor_passive.c            | 1 +
 drivers/devfreq/governor_performance.c        | 1 +
 drivers/devfreq/governor_powersave.c          | 1 +
 drivers/devfreq/governor_simpleondemand.c     | 1 +
 drivers/devfreq/governor_userspace.c          | 1 +
 drivers/devfreq/hisi_uncore_freq.c            | 1 +
 drivers/devfreq/tegra30-devfreq.c             | 3 ++-
 include/linux/devfreq-governor.h              | 3 +++
 10 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
index df8ba88b9f6a..5be9940a5853 100644
--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -37,6 +37,14 @@ Description:
 		The /sys/class/devfreq/.../target_freq shows the next governor
 		predicted target frequency of the corresponding devfreq object.
 
+		Reading this attribute returns -EINVAL when the active
+		governor does not advertise DEVFREQ_GOV_ATTR_TARGET_FREQ.
+		All in-tree governors that drive frequency transitions tag
+		this attribute, so existing in-tree behaviour is unchanged.
+		Out-of-tree governors that previously relied on the
+		unconditional read of df->previous_freq must opt in by
+		setting DEVFREQ_GOV_ATTR_TARGET_FREQ in their attrs field.
+
 What:		/sys/class/devfreq/.../trans_stat
 Date:		October 2012
 Contact:	MyungJoo Ham <[email protected]>
diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index f08fc6966eae..2f27a239e34a 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -1530,6 +1530,12 @@ static ssize_t target_freq_show(struct device *dev,
 {
 	struct devfreq *df = to_devfreq(dev);
 
+	guard(mutex)(&devfreq_list_lock);
+
+	if (!df->profile || !df->governor ||
+	    !IS_SUPPORTED_ATTR(df->governor->attrs, TARGET_FREQ))
+		return -EINVAL;
+
 	return sprintf(buf, "%lu\n", df->previous_freq);
 }
 static DEVICE_ATTR_RO(target_freq);
diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
index d7feecd900f1..b75e4bbee4b1 100644
--- a/drivers/devfreq/governor_passive.c
+++ b/drivers/devfreq/governor_passive.c
@@ -448,6 +448,7 @@ static int devfreq_passive_event_handler(struct devfreq *devfreq,
 
 static struct devfreq_governor devfreq_passive = {
 	.name = DEVFREQ_GOV_PASSIVE,
+	.attrs = DEVFREQ_GOV_ATTR_TARGET_FREQ,
 	.flags = DEVFREQ_GOV_FLAG_IMMUTABLE,
 	.get_target_freq = devfreq_passive_get_target_freq,
 	.event_handler = devfreq_passive_event_handler,
diff --git a/drivers/devfreq/governor_performance.c b/drivers/devfreq/governor_performance.c
index fdb22bf512cf..b9ec587f582c 100644
--- a/drivers/devfreq/governor_performance.c
+++ b/drivers/devfreq/governor_performance.c
@@ -37,6 +37,7 @@ static int devfreq_performance_handler(struct devfreq *devfreq,
 
 static struct devfreq_governor devfreq_performance = {
 	.name = DEVFREQ_GOV_PERFORMANCE,
+	.attrs = DEVFREQ_GOV_ATTR_TARGET_FREQ,
 	.get_target_freq = devfreq_performance_func,
 	.event_handler = devfreq_performance_handler,
 };
diff --git a/drivers/devfreq/governor_powersave.c b/drivers/devfreq/governor_powersave.c
index ee2d6ec8a512..69eab1d0a7fc 100644
--- a/drivers/devfreq/governor_powersave.c
+++ b/drivers/devfreq/governor_powersave.c
@@ -37,6 +37,7 @@ static int devfreq_powersave_handler(struct devfreq *devfreq,
 
 static struct devfreq_governor devfreq_powersave = {
 	.name = DEVFREQ_GOV_POWERSAVE,
+	.attrs = DEVFREQ_GOV_ATTR_TARGET_FREQ,
 	.get_target_freq = devfreq_powersave_func,
 	.event_handler = devfreq_powersave_handler,
 };
diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
index ac9c5e9e51a4..65ff9d912ef9 100644
--- a/drivers/devfreq/governor_simpleondemand.c
+++ b/drivers/devfreq/governor_simpleondemand.c
@@ -118,6 +118,7 @@ static int devfreq_simple_ondemand_handler(struct devfreq *devfreq,
 static struct devfreq_governor devfreq_simple_ondemand = {
 	.name = DEVFREQ_GOV_SIMPLE_ONDEMAND,
 	.attrs = DEVFREQ_GOV_ATTR_POLLING_INTERVAL
+		| DEVFREQ_GOV_ATTR_TARGET_FREQ
 		| DEVFREQ_GOV_ATTR_TIMER,
 	.get_target_freq = devfreq_simple_ondemand_func,
 	.event_handler = devfreq_simple_ondemand_handler,
diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
index 3906ebedbae8..d1b765a7b8e5 100644
--- a/drivers/devfreq/governor_userspace.c
+++ b/drivers/devfreq/governor_userspace.c
@@ -135,6 +135,7 @@ static int devfreq_userspace_handler(struct devfreq *devfreq,
 
 static struct devfreq_governor devfreq_userspace = {
 	.name = DEVFREQ_GOV_USERSPACE,
+	.attrs = DEVFREQ_GOV_ATTR_TARGET_FREQ,
 	.get_target_freq = devfreq_userspace_func,
 	.event_handler = devfreq_userspace_handler,
 };
diff --git a/drivers/devfreq/hisi_uncore_freq.c b/drivers/devfreq/hisi_uncore_freq.c
index e1f64b723082..5a2d7e011ad1 100644
--- a/drivers/devfreq/hisi_uncore_freq.c
+++ b/drivers/devfreq/hisi_uncore_freq.c
@@ -398,6 +398,7 @@ static struct devfreq_governor hisi_platform_governor = {
 	 * Set interrupt_driven to skip the devfreq monitor mechanism, though
 	 * this governor is not interrupt-driven.
 	 */
+	.attrs = DEVFREQ_GOV_ATTR_TARGET_FREQ,
 	.flags = DEVFREQ_GOV_FLAG_IRQ_DRIVEN,
 	.get_target_freq = hisi_platform_gov_func,
 	.event_handler = hisi_platform_gov_handler,
diff --git a/drivers/devfreq/tegra30-devfreq.c b/drivers/devfreq/tegra30-devfreq.c
index 401aac6a9f07..fcb278c4a74c 100644
--- a/drivers/devfreq/tegra30-devfreq.c
+++ b/drivers/devfreq/tegra30-devfreq.c
@@ -776,7 +776,8 @@ static int tegra_governor_event_handler(struct devfreq *devfreq,
 
 static struct devfreq_governor tegra_devfreq_governor = {
 	.name = "tegra_actmon",
-	.attrs = DEVFREQ_GOV_ATTR_POLLING_INTERVAL,
+	.attrs = DEVFREQ_GOV_ATTR_POLLING_INTERVAL
+		| DEVFREQ_GOV_ATTR_TARGET_FREQ,
 	.flags = DEVFREQ_GOV_FLAG_IMMUTABLE
 		| DEVFREQ_GOV_FLAG_IRQ_DRIVEN,
 	.get_target_freq = tegra_governor_get_target,
diff --git a/include/linux/devfreq-governor.h b/include/linux/devfreq-governor.h
index dfdd0160a29f..2853f571dfdf 100644
--- a/include/linux/devfreq-governor.h
+++ b/include/linux/devfreq-governor.h
@@ -43,9 +43,12 @@
  *   : Indicate polling_interval sysfs attribute
  * - DEVFREQ_GOV_ATTR_TIMER
  *   : Indicate timer sysfs attribute
+ * - DEVFREQ_GOV_ATTR_TARGET_FREQ
+ *   : Indicate the target freq sysfs attribute
  */
 #define DEVFREQ_GOV_ATTR_POLLING_INTERVAL		BIT(0)
 #define DEVFREQ_GOV_ATTR_TIMER				BIT(1)
+#define DEVFREQ_GOV_ATTR_TARGET_FREQ			BIT(2)
 
 /**
  * struct devfreq_governor - Devfreq policy governor

-- 
2.34.1