[PATCH v4 03/11] power: sequencing: Add pwrseq_is_controllable() API

[Loic Poulain <loic.poulain@oss.qualcomm.com>]

On some boards a power sequencing target has no host-controllable enable
for its function, for instance when the enable line is not wired up to a
GPIO and is hardwired to an always-on level. The pcie-m2 "uart" target is
one such example: when the M.2 connector does not route the W_DISABLE2#
signal to a host GPIO, its enable/disable are no-ops and the consumer
cannot gate the Bluetooth function at all or exclusively.

Add a generic pwrseq_is_controllable() helper. It reports whether the
target's final unit provides a host-controllable dedicated power actuator.
The target can implement a new optional is_controllable() callback,
reporting whether that actuator is effective on this target (for example
depending on GPIO presence). If the target does not provide the callback,
it is assumed to be controllable.

Note this only describes the target's own enable actuator. It does not
imply that a power-off reaches an electrical OFF state, since a target may
have multiple consumers. It also does not mean that power is uncontrolled
for the target's dependencies: those may still be gated on their own. And
it does not restrict consumers from calling pwrseq_power_off() either,
which remains valid to drop this consumer's vote on the (possibly shared)
resources and dependencies of the target.

Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 drivers/power/sequencing/core.c | 49 +++++++++++++++++++++++++++++++++++++++++
 include/linux/pwrseq/consumer.h |  7 ++++++
 include/linux/pwrseq/provider.h |  8 +++++++
 3 files changed, 64 insertions(+)

diff --git a/drivers/power/sequencing/core.c b/drivers/power/sequencing/core.c
index 02f42da915985339d3de507fc36dd158b0035a99..cabb3d0885f94d9d70e0631861ed6905d91ad3bc 100644
--- a/drivers/power/sequencing/core.c
+++ b/drivers/power/sequencing/core.c
@@ -182,12 +182,15 @@ static void pwrseq_unit_release(struct kref *ref)
  *               the state lock has been released. It's useful for implementing
  *               boot-up delays without blocking other users from powering up
  *               using the same power sequencer.
+ * @is_controllable: Optional callback reporting whether enabling/disabling
+ *                   this target actually controls power.
  */
 struct pwrseq_target {
 	struct list_head list;
 	const char *name;
 	struct pwrseq_unit *unit;
 	pwrseq_power_state_func post_enable;
+	pwrseq_is_controllable_func is_controllable;
 };
 
 static struct pwrseq_target *
@@ -206,6 +209,7 @@ pwrseq_target_new(const struct pwrseq_target_data *data)
 	}
 
 	target->post_enable = data->post_enable;
+	target->is_controllable = data->is_controllable;
 
 	return target;
 }
@@ -991,6 +995,51 @@ struct device *pwrseq_to_device(struct pwrseq_desc *desc)
 }
 EXPORT_SYMBOL_GPL(pwrseq_to_device);
 
+/**
+ * pwrseq_is_controllable() - Check whether the target provides a
+ *                            host-controllable power actuator.
+ * @desc: Descriptor referencing the power sequencer.
+ *
+ * Some power sequencing targets provide no host-controllable enable for their
+ * function on a given board, for instance when the enable line is not wired up
+ * and is instead hardwired to an always-on level. For such targets a call to
+ * pwrseq_power_off() is still allowed, so that the consumer can drop its vote
+ * on the (possibly shared) resources, but the host cannot gate the function
+ * on its own.
+ *
+ * Returns:
+ * True if the target provides a host-controllable power actuator, false
+ * otherwise. Also returns false if @desc is NULL.
+ */
+bool pwrseq_is_controllable(struct pwrseq_desc *desc)
+{
+	struct pwrseq_device *pwrseq;
+	struct pwrseq_target *target;
+	struct pwrseq_unit *unit;
+
+	might_sleep();
+
+	if (!desc)
+		return false;
+
+	pwrseq = desc->pwrseq;
+	target = desc->target;
+	unit = target->unit;
+
+	guard(rwsem_read)(&pwrseq->rw_lock);
+	if (!device_is_registered(&pwrseq->dev))
+		return false;
+
+	if (!unit->enable && !unit->disable)
+		return false;
+
+	if (!target->is_controllable)
+		return true;
+
+	return target->is_controllable(pwrseq);
+}
+EXPORT_SYMBOL_GPL(pwrseq_is_controllable);
+
 #if IS_ENABLED(CONFIG_DEBUG_FS)
 
 struct pwrseq_debugfs_count_ctx {
diff --git a/include/linux/pwrseq/consumer.h b/include/linux/pwrseq/consumer.h
index 3c907c9e1885dc2958043a9a733fbe20bdf95f6e..f70f694c19ab73f70ccf775aa24902bfcc982a42 100644
--- a/include/linux/pwrseq/consumer.h
+++ b/include/linux/pwrseq/consumer.h
@@ -25,6 +25,8 @@ int pwrseq_power_off(struct pwrseq_desc *desc);
 
 struct device *pwrseq_to_device(struct pwrseq_desc *desc);
 
+bool pwrseq_is_controllable(struct pwrseq_desc *desc);
+
 #else /* CONFIG_POWER_SEQUENCING */
 
 static inline struct pwrseq_desc * __must_check
@@ -58,6 +60,11 @@ static inline struct device *pwrseq_to_device(struct pwrseq_desc *desc)
 	return NULL;
 }
 
+static inline bool pwrseq_is_controllable(struct pwrseq_desc *desc)
+{
+	return false;
+}
+
 #endif /* CONFIG_POWER_SEQUENCING */
 
 #endif /* __POWER_SEQUENCING_CONSUMER_H__ */
diff --git a/include/linux/pwrseq/provider.h b/include/linux/pwrseq/provider.h
index 33b3d2c2e39decafac6c6fca9254ad4329d90e94..7285ad94a2214070a1c27f25c783f51105705b36 100644
--- a/include/linux/pwrseq/provider.h
+++ b/include/linux/pwrseq/provider.h
@@ -6,12 +6,15 @@
 #ifndef __POWER_SEQUENCING_PROVIDER_H__
 #define __POWER_SEQUENCING_PROVIDER_H__
 
+#include <linux/types.h>
+
 struct device;
 struct module;
 struct pwrseq_device;
 
 typedef int (*pwrseq_power_state_func)(struct pwrseq_device *);
 typedef int (*pwrseq_match_func)(struct pwrseq_device *, struct device *);
+typedef bool (*pwrseq_is_controllable_func)(struct pwrseq_device *);
 
 #define PWRSEQ_NO_MATCH 0
 #define PWRSEQ_MATCH_OK 1
@@ -43,11 +46,16 @@ struct pwrseq_unit_data {
  *               the state lock has been released. It's useful for implementing
  *               boot-up delays without blocking other users from powering up
  *               using the same power sequencer.
+ * @is_controllable: Optional callback checking whether enabling/disabling this
+ *                   target actually controls power (for example when the
+ *                   controlling GPIO is wired up). If not provided, the
+ *                   target's power is assumed to be always controllable.
  */
 struct pwrseq_target_data {
 	const char *name;
 	const struct pwrseq_unit_data *unit;
 	pwrseq_power_state_func post_enable;
+	pwrseq_is_controllable_func is_controllable;
 };
 
 /**

-- 
2.34.1