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SubjectRe: [PATCH v8 17/22] counter: Add character device interface
On Fri, 12 Feb 2021 21:13:41 +0900
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> This patch introduces a character device interface for the Counter
> subsystem. Device data is exposed through standard character device read
> operations. Device data is gathered when a Counter event is pushed by
> the respective Counter device driver. Configuration is handled via ioctl
> operations on the respective Counter character device node.
>
> Cc: David Lechner <david@lechnology.com>
> Cc: Gwendal Grignou <gwendal@chromium.org>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: Oleksij Rempel <o.rempel@pengutronix.de>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>

Hi William,

A few minor comments. Mostly seems to have come together well and
makes sense to me.

Jonathan

> ---
> drivers/counter/Makefile | 2 +-
> drivers/counter/counter-chrdev.c | 496 +++++++++++++++++++++++++++++++
> drivers/counter/counter-chrdev.h | 16 +
> drivers/counter/counter-core.c | 37 ++-
> include/linux/counter.h | 45 +++
> include/uapi/linux/counter.h | 70 +++++
> 6 files changed, 661 insertions(+), 5 deletions(-)
> create mode 100644 drivers/counter/counter-chrdev.c
> create mode 100644 drivers/counter/counter-chrdev.h
>

...

> diff --git a/drivers/counter/counter-core.c b/drivers/counter/counter-core.c
> index bcf672e1fc0d..c137fcb97d9c 100644
> --- a/drivers/counter/counter-core.c
> +++ b/drivers/counter/counter-core.c
> @@ -5,12 +5,16 @@
> */
> #include <linux/counter.h>
> #include <linux/device.h>
> +#include <linux/device/bus.h>
> #include <linux/export.h>
> +#include <linux/fs.h>
> #include <linux/gfp.h>
> #include <linux/idr.h>
> #include <linux/init.h>
> #include <linux/module.h>
> +#include <linux/types.h>
>
> +#include "counter-chrdev.h"
> #include "counter-sysfs.h"
>
> /* Provides a unique ID for each counter device */
> @@ -33,6 +37,8 @@ static struct bus_type counter_bus_type = {
> .name = "counter"
> };
>
> +static dev_t counter_devt;
> +
> /**
> * counter_register - register Counter to the system
> * @counter: pointer to Counter to register
> @@ -54,7 +60,6 @@ int counter_register(struct counter_device *const counter)
> if (counter->id < 0)
> return counter->id;
>
> - /* Configure device structure for Counter */

Not sure why this comment gets removed here.

> dev->type = &counter_device_type;
> dev->bus = &counter_bus_type;
> if (counter->parent) {
> @@ -65,18 +70,25 @@ int counter_register(struct counter_device *const counter)
> device_initialize(dev);
> dev_set_drvdata(dev, counter);
>
> + /* Add Counter character device */
> + err = counter_chrdev_add(counter, counter_devt);
> + if (err < 0)
> + goto err_free_id;
> +
> /* Add Counter sysfs attributes */
> err = counter_sysfs_add(counter);
> if (err < 0)
> - goto err_free_id;
> + goto err_remove_chrdev;
>
> /* Add device to system */
> err = device_add(dev);
> if (err < 0)
> - goto err_free_id;
> + goto err_remove_chrdev;

It might be worth thinking about using cdev_device_add()
though will require a slightly different order of adding.


>
> return 0;
>
> +err_remove_chrdev:
> + counter_chrdev_remove(counter);
> err_free_id:
> put_device(dev);
> return err;
> @@ -138,13 +150,30 @@ int devm_counter_register(struct device *dev,
> }
> EXPORT_SYMBOL_GPL(devm_counter_register);
>
> +#define COUNTER_DEV_MAX 256
> +
> static int __init counter_init(void)
> {
> - return bus_register(&counter_bus_type);
> + int err;
> +
> + err = bus_register(&counter_bus_type);
> + if (err < 0)
> + return err;
> +
> + err = alloc_chrdev_region(&counter_devt, 0, COUNTER_DEV_MAX, "counter");
> + if (err < 0)
> + goto err_unregister_bus;
> +
> + return 0;
> +
> +err_unregister_bus:
> + bus_unregister(&counter_bus_type);
> + return err;
> }
>
> static void __exit counter_exit(void)
> {
> + unregister_chrdev_region(counter_devt, COUNTER_DEV_MAX);
> bus_unregister(&counter_bus_type);
> }
>

...

> diff --git a/include/uapi/linux/counter.h b/include/uapi/linux/counter.h
> index 6113938a6044..3d647a5383b8 100644
> --- a/include/uapi/linux/counter.h
> +++ b/include/uapi/linux/counter.h
> @@ -6,6 +6,19 @@
> #ifndef _UAPI_COUNTER_H_
> #define _UAPI_COUNTER_H_
>
> +#include <linux/ioctl.h>
> +#include <linux/types.h>
> +
> +/* Component type definitions */
> +enum counter_component_type {
> + COUNTER_COMPONENT_NONE,
> + COUNTER_COMPONENT_SIGNAL,
> + COUNTER_COMPONENT_COUNT,
> + COUNTER_COMPONENT_FUNCTION,
> + COUNTER_COMPONENT_SYNAPSE_ACTION,
> + COUNTER_COMPONENT_EXTENSION,
> +};
> +
> /* Component scope definitions */
> enum counter_scope {
> COUNTER_SCOPE_DEVICE,
> @@ -13,6 +26,63 @@ enum counter_scope {
> COUNTER_SCOPE_COUNT,
> };
>
> +/**
> + * struct counter_component - Counter component identification
> + * @type: component type (one of enum counter_component_type)
> + * @scope: component scope (one of enum counter_scope)
> + * @parent: parent component ID (matching the Y/Z suffix of the respective sysfs
> + * path as described in Documentation/ABI/testing/sysfs-bus-counter)

Probably good to give an example here as well as the cross reference.

> + * @id: component ID (matching the Y/Z suffix of the respective sysfs path as
> + * described in Documentation/ABI/testing/sysfs-bus-counter)
> + */
> +struct counter_component {
> + __u8 type;
> + __u8 scope;
> + __u8 parent;
> + __u8 id;
> +};
> +
> +/* Event type definitions */
> +enum counter_event_type {
> + COUNTER_EVENT_OVERFLOW,
> + COUNTER_EVENT_UNDERFLOW,
> + COUNTER_EVENT_OVERFLOW_UNDERFLOW,
> + COUNTER_EVENT_THRESHOLD,
> + COUNTER_EVENT_INDEX,
> +};
> +
> +/**
> + * struct counter_watch - Counter component watch configuration
> + * @component: component to watch when event triggers
> + * @event: event that triggers (one of enum counter_event_type)
> + * @channel: event channel (typically 0 unless the device supports concurrent
> + * events of the same type)
> + */
> +struct counter_watch {
> + struct counter_component component;
> + __u8 event;
> + __u8 channel;
> +};
> +
> +/* ioctl commands */
> +#define COUNTER_ADD_WATCH_IOCTL _IOW(0x3E, 0x00, struct counter_watch)
> +#define COUNTER_ENABLE_EVENTS_IOCTL _IO(0x3E, 0x01)
> +#define COUNTER_DISABLE_EVENTS_IOCTL _IO(0x3E, 0x02)
> +
> +/**
> + * struct counter_event - Counter event data
> + * @timestamp: best estimate of time of event occurrence, in nanoseconds
> + * @value: component value
> + * @watch: component watch configuration
> + * @status: return status (system error number)
> + */
> +struct counter_event {
> + __aligned_u64 timestamp;
> + __aligned_u64 value;
> + struct counter_watch watch;
> + __u8 status;
> +};
> +
> /* Count direction values */
> enum counter_count_direction {
> COUNTER_COUNT_DIRECTION_FORWARD,

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