On Sun, Feb 14, 2021 at 06:11:46PM +0000, Jonathan Cameron wrote: > On Fri, 12 Feb 2021 21:13:44 +0900 > William Breathitt Gray 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 > > Signed-off-by: William Breathitt Gray > > --- > > 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? We take the events_list_lock down below so we're safe against missing an event, but past events currently unread in the queue will be lost. Shortening the size of the queue is inherently a destructive process if we have more events in the current queue than can fit in the new queue. Because we a liable to lose some events in such a case, I think it's best to keep the behavior of this reallocation consistent and have it provide a fresh empty queue every time, as opposed to sometimes dropping events and sometimes not. I also suspect an actual user would be setting the size of their queue to the required amount before they begin watching events, rather than adjusting it sporadically during a live operation. > > + 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 > > #include > > > > +#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? Ack. William Breathitt Gray > > + 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; >