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SubjectRe: [PATCH v8 20/22] counter: Implement events_queue_size sysfs attribute
On Fri, 12 Feb 2021 21:13:44 +0900
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> 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);

Is there any potential for losing events?

> + 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;

kfifo_size() rather than open coding it?

> + 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;

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