[PATCH v8 20/22] counter: Implement events_queue_size sysfs attribute

[William Breathitt Gray <vilhelm.gray@gmail.com>]

The events_queue_size sysfs attribute provides a way for users to
dynamically configure the Counter events queue size for the Counter
character device interface. The size is in number of struct
counter_event data structures. The number of elements will be rounded-up
to a power of 2 due to a requirement of the kfifo_alloc function called
during reallocation of the queue.

Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
 Documentation/ABI/testing/sysfs-bus-counter |  8 +++++++
 drivers/counter/counter-chrdev.c            | 23 +++++++++++++++++++
 drivers/counter/counter-chrdev.h            |  2 ++
 drivers/counter/counter-sysfs.c             | 25 +++++++++++++++++++++
 4 files changed, 58 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-counter b/Documentation/ABI/testing/sysfs-bus-counter
index 847e96f19d19..f6cb2a8b08a7 100644
--- a/Documentation/ABI/testing/sysfs-bus-counter
+++ b/Documentation/ABI/testing/sysfs-bus-counter
@@ -212,6 +212,14 @@ Description:
 		both edges:
 			Any state transition.
 
+What:		/sys/bus/counter/devices/counterX/events_queue_size
+KernelVersion:	5.13
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Size of the Counter events queue in number of struct
+		counter_event data structures. The number of elements will be
+		rounded-up to a power of 2.
+
 What:		/sys/bus/counter/devices/counterX/name
 KernelVersion:	5.2
 Contact:	linux-iio@vger.kernel.org
diff --git a/drivers/counter/counter-chrdev.c b/drivers/counter/counter-chrdev.c
index 16f02df7f73d..53eea894e13f 100644
--- a/drivers/counter/counter-chrdev.c
+++ b/drivers/counter/counter-chrdev.c
@@ -375,6 +375,29 @@ void counter_chrdev_remove(struct counter_device *const counter)
 	cdev_del(&counter->chrdev);
 }
 
+int counter_chrdev_realloc_queue(struct counter_device *const counter,
+				 size_t queue_size)
+{
+	int err;
+	DECLARE_KFIFO_PTR(events, struct counter_event);
+	unsigned long flags;
+
+	/* Allocate new events queue */
+	err = kfifo_alloc(&events, queue_size, GFP_ATOMIC);
+	if (err)
+		return err;
+
+	raw_spin_lock_irqsave(&counter->events_list_lock, flags);
+
+	/* Swap in new events queue */
+	kfifo_free(&counter->events);
+	counter->events.kfifo = events.kfifo;
+
+	raw_spin_unlock_irqrestore(&counter->events_list_lock, flags);
+
+	return 0;
+}
+
 static int counter_get_data(struct counter_device *const counter,
 			    const struct counter_comp_node *const comp_node,
 			    u64 *const value)
diff --git a/drivers/counter/counter-chrdev.h b/drivers/counter/counter-chrdev.h
index cf5a318fe540..ff7fb0191852 100644
--- a/drivers/counter/counter-chrdev.h
+++ b/drivers/counter/counter-chrdev.h
@@ -12,5 +12,7 @@
 int counter_chrdev_add(struct counter_device *const counter,
 		       const dev_t counter_devt);
 void counter_chrdev_remove(struct counter_device *const counter);
+int counter_chrdev_realloc_queue(struct counter_device *const counter,
+				 size_t queue_size);
 
 #endif /* _COUNTER_CHRDEV_H_ */
diff --git a/drivers/counter/counter-sysfs.c b/drivers/counter/counter-sysfs.c
index 0cb3dba950bc..9abc821a3871 100644
--- a/drivers/counter/counter-sysfs.c
+++ b/drivers/counter/counter-sysfs.c
@@ -13,6 +13,7 @@
 #include <linux/sysfs.h>
 #include <linux/types.h>
 
+#include "counter-chrdev.h"
 #include "counter-sysfs.h"
 
 /**
@@ -737,12 +738,30 @@ static int counter_num_counts_read(struct counter_device *counter, u8 *val)
 	return 0;
 }
 
+static int counter_events_queue_size_read(struct counter_device *counter,
+					  u64 *val)
+{
+	*val = counter->events.kfifo.mask + 1;
+	return 0;
+}
+
+static int counter_events_queue_size_write(struct counter_device *counter,
+					   u64 val)
+{
+	return counter_chrdev_realloc_queue(counter, val);
+}
+
 static struct counter_comp counter_num_signals_comp =
 	COUNTER_COMP_DEVICE_U8("num_signals", counter_num_signals_read, NULL);
 
 static struct counter_comp counter_num_counts_comp =
 	COUNTER_COMP_DEVICE_U8("num_counts", counter_num_counts_read, NULL);
 
+static struct counter_comp counter_events_queue_size_comp =
+	COUNTER_COMP_DEVICE_U64("events_queue_size",
+				counter_events_queue_size_read,
+				counter_events_queue_size_write);
+
 static int counter_sysfs_attr_add(struct counter_device *const counter,
 				  struct counter_attribute_group *group)
 {
@@ -781,6 +800,12 @@ static int counter_sysfs_attr_add(struct counter_device *const counter,
 	if (err < 0)
 		return err;
 
+	/* Create num_counts attribute */
+	err = counter_attr_create(dev, group, &counter_events_queue_size_comp,
+				  scope, NULL);
+	if (err < 0)
+		return err;
+
 	/* Create an attribute for each extension */
 	for (i = 0; i < counter->num_ext; i++) {
 		ext = counter->ext + i;
-- 
2.30.0