counter: Implement events_queue_size sysfs attribute

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>
Link: https://lore.kernel.org/r/c914b2db2ea0a2637633bcc3e86ded3c94783f2e.1632884256.git.vilhelm.gray@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/Documentation/ABI/testing/sysfs-bus-counter b/Documentation/ABI/testing/sysfs-bus-counter
index 0ce1666..06c2b3e 100644 (file)
--- 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: 5.16
+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-sysfs.c b/drivers/counter/counter-sysfs.c
index 97d8d7c..1ccd771 100644 (file)
--- a/drivers/counter/counter-sysfs.c
+++ b/drivers/counter/counter-sysfs.c
@@ -3,11 +3,13 @@
  * Generic Counter sysfs interface
  * Copyright (C) 2020 William Breathitt Gray
  */
+#include <linux/atomic.h>
 #include <linux/counter.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/gfp.h>
 #include <linux/kernel.h>
+#include <linux/kfifo.h>
 #include <linux/kstrtox.h>
 #include <linux/list.h>
 #include <linux/string.h>
@@ -783,12 +785,49 @@ 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)
+{
+       DECLARE_KFIFO_PTR(events, struct counter_event);
+       int err = 0;
+
+       /* Ensure chrdev is not opened more than 1 at a time */
+       if (!atomic_add_unless(&counter->chrdev_lock, 1, 1))
+               return -EBUSY;
+
+       /* Allocate new events queue */
+       err = kfifo_alloc(&events, val, GFP_KERNEL);
+       if (err)
+               goto exit_early;
+
+       /* Swap in new events queue */
+       kfifo_free(&counter->events);
+       counter->events.kfifo = events.kfifo;
+
+exit_early:
+       atomic_dec(&counter->chrdev_lock);
+
+       return err;
+}
+
 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 *cattr_group)
 {
@@ -827,6 +866,12 @@ static int counter_sysfs_attr_add(struct counter_device *const counter,
        if (err < 0)
                return err;
 
+       /* Create events_queue_size attribute */
+       err = counter_attr_create(dev, cattr_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];