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Subject[PATCH v12 15/17] counter: Implement events_queue_size sysfs attribute
Date
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 | 4 ++
drivers/counter/counter-sysfs.c | 44 +++++++++++++++++++++
include/linux/counter.h | 2 +
4 files changed, 58 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-counter b/Documentation/ABI/testing/sysfs-bus-counter
index e0e99adb0ecc..84ebb1ed28ed 100644
--- a/Documentation/ABI/testing/sysfs-bus-counter
+++ b/Documentation/ABI/testing/sysfs-bus-counter
@@ -233,6 +233,14 @@ Description:
shorter or equal to configured value are ignored. Value 0 means
filter is disabled.

+What: /sys/bus/counter/devices/counterX/events_queue_size
+KernelVersion: 5.15
+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 92805b1f65b8..13644c87d02a 100644
--- a/drivers/counter/counter-chrdev.c
+++ b/drivers/counter/counter-chrdev.c
@@ -323,6 +323,9 @@ static int counter_chrdev_open(struct inode *inode, struct file *filp)
typeof(*counter),
chrdev);

+ if (!mutex_trylock(&counter->chrdev_lock))
+ return -EBUSY;
+
get_device(&counter->dev);
filp->private_data = counter;

@@ -339,6 +342,7 @@ static int counter_chrdev_release(struct inode *inode, struct file *filp)
return err;

put_device(&counter->dev);
+ mutex_unlock(&counter->chrdev_lock);

return 0;
}
diff --git a/drivers/counter/counter-sysfs.c b/drivers/counter/counter-sysfs.c
index eb1505bfbd89..bf038eff4587 100644
--- a/drivers/counter/counter-sysfs.c
+++ b/drivers/counter/counter-sysfs.c
@@ -8,7 +8,9 @@
#include <linux/err.h>
#include <linux/gfp.h>
#include <linux/kernel.h>
+#include <linux/kfifo.h>
#include <linux/list.h>
+#include <linux/mutex.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/types.h>
@@ -782,12 +784,48 @@ 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 = kfifo_size(&counter->events);
+ return 0;
+}
+
+static int counter_events_queue_size_write(struct counter_device *counter,
+ u64 val)
+{
+ int err;
+ DECLARE_KFIFO_PTR(events, struct counter_event);
+
+ /* Verify chrdev is not currently being used */
+ if (!mutex_trylock(&counter->chrdev_lock))
+ return -EBUSY;
+
+ /* Allocate new events queue */
+ err = kfifo_alloc(&events, val, GFP_ATOMIC);
+ if (err)
+ return err;
+
+ /* Swap in new events queue */
+ kfifo_free(&counter->events);
+ counter->events.kfifo = events.kfifo;
+
+ mutex_unlock(&counter->chrdev_lock);
+
+ return 0;
+}
+
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)
{
@@ -826,6 +864,12 @@ 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;
diff --git a/include/linux/counter.h b/include/linux/counter.h
index 3f0bbe4ff702..854fcaf49c32 100644
--- a/include/linux/counter.h
+++ b/include/linux/counter.h
@@ -289,6 +289,7 @@ struct counter_ops {
* @priv: optional private data supplied by driver
* @dev: internal device structure
* @chrdev: internal character device structure
+ * @chrdev_lock: lock to limit chrdev to a single open at a time
* @events_list: list of current watching Counter events
* @events_list_lock: lock to protect Counter events list operations
* @next_events_list: list of next watching Counter events
@@ -314,6 +315,7 @@ struct counter_device {

struct device dev;
struct cdev chrdev;
+ struct mutex chrdev_lock;
struct list_head events_list;
spinlock_t events_list_lock;
struct list_head next_events_list;
--
2.32.0
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