Re: [PATCH v4 1/4] iio: core: Introduce IIO software triggers

[Jonathan Cameron <jic23@kernel.org>]

On 20/04/15 15:02, Daniel Baluta wrote:
> A software trigger associates an IIO device trigger with a software
> interrupt source (e.g: timer, sysfs). This patch adds the generic
> infrastructure for handling software triggers.
> 
> Software interrupts sources are kept in a iio_trigger_types_list and
> registered separately when the associated kernel module is loaded.
> 
> Software triggers can be created directly from drivers or from user
> space via configfs interface.
> 
> Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Looks sensible.
My only real question is if the rwlock is justified (vs a mutex).

> ---
>  drivers/iio/Kconfig                   |   8 +++
>  drivers/iio/Makefile                  |   1 +
>  drivers/iio/industrialio-sw-trigger.c | 111 ++++++++++++++++++++++++++++++++++
>  include/linux/iio/sw_trigger.h        |  50 +++++++++++++++
>  4 files changed, 170 insertions(+)
>  create mode 100644 drivers/iio/industrialio-sw-trigger.c
>  create mode 100644 include/linux/iio/sw_trigger.h
> 
> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
> index 4011eff..de7f1d9 100644
> --- a/drivers/iio/Kconfig
> +++ b/drivers/iio/Kconfig
> @@ -58,6 +58,14 @@ config IIO_CONSUMERS_PER_TRIGGER
>  	This value controls the maximum number of consumers that a
>  	given trigger may handle. Default is 2.
>  
> +config IIO_SW_TRIGGER
> +	bool "Enable software triggers support"
> +	depends on IIO_TRIGGER
> +	help
> +	 Provides IIO core support for software triggers. A software
> +	 trigger can be created via configfs or directly by a driver
> +	 using the API provided.
> +
>  source "drivers/iio/accel/Kconfig"
>  source "drivers/iio/adc/Kconfig"
>  source "drivers/iio/amplifiers/Kconfig"
> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
> index 698afc2..df87975 100644
> --- a/drivers/iio/Makefile
> +++ b/drivers/iio/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_IIO) += industrialio.o
>  industrialio-y := industrialio-core.o industrialio-event.o inkern.o
>  industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
>  industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
> +industrialio-$(CONFIG_IIO_SW_TRIGGER) += industrialio-sw-trigger.o
>  industrialio-$(CONFIG_IIO_BUFFER_CB) += buffer_cb.o
>  
>  obj-$(CONFIG_IIO_TRIGGERED_BUFFER) += industrialio-triggered-buffer.o
> diff --git a/drivers/iio/industrialio-sw-trigger.c b/drivers/iio/industrialio-sw-trigger.c
> new file mode 100644
> index 0000000..567c675
> --- /dev/null
> +++ b/drivers/iio/industrialio-sw-trigger.c
> @@ -0,0 +1,111 @@
> +/*
> + * The Industrial I/O core, software trigger functions
> + *
> + * Copyright (c) 2015 Intel Corporation
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/kmod.h>
> +#include <linux/list.h>
> +#include <linux/slab.h>
> +
> +#include <linux/iio/sw_trigger.h>
> +
> +static LIST_HEAD(iio_trigger_types_list);
> +static DEFINE_RWLOCK(iio_trigger_types_lock);
Can see the logic, but I'm not totally convinced a rwlock is necessary.
We don't actually create new ones terribly often...
> +
> +static
> +struct iio_sw_trigger_type *iio_find_sw_trigger_type(char *name, unsigned len)
> +{
> +	struct iio_sw_trigger_type *t = NULL, *iter;
> +
> +	list_for_each_entry(iter, &iio_trigger_types_list, list)
> +		if (!strncmp(iter->name, name, len)) {
> +			t = iter;
> +			break;
> +		}
> +
> +	return t;
> +}
> +
> +int iio_register_sw_trigger_type(struct iio_sw_trigger_type *t)
> +{
> +	struct iio_sw_trigger_type *iter;
> +	int ret = 0;
> +
> +	write_lock(&iio_trigger_types_lock);
> +	iter = iio_find_sw_trigger_type(t->name, strlen(t->name));
> +	if (iter)
> +		ret = -EBUSY;
Rather than EAGAIN?  Could also do the magic attempt to autoload the
module that the usb gadget driver does (though add that as a later
feature rather than in this first posting I think to keep complexity
of patch manageable).
> +	else
> +		list_add_tail(&t->list, &iio_trigger_types_list);
> +	write_unlock(&iio_trigger_types_lock);
nitpick :) blank line here.
> +	return ret;
> +}
> +EXPORT_SYMBOL(iio_register_sw_trigger_type);
> +
> +int iio_unregister_sw_trigger_type(struct iio_sw_trigger_type *t)
> +{
> +	struct iio_sw_trigger_type *iter;
> +	int ret = 0;
> +
> +	write_lock(&iio_trigger_types_lock);
> +	iter = iio_find_sw_trigger_type(t->name, strlen(t->name));
> +	if (!iter)
> +		ret = -EINVAL;
> +	else
> +		list_del(&t->list);
> +	write_unlock(&iio_trigger_types_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(iio_unregister_sw_trigger_type);
> +
> +static
> +struct iio_sw_trigger_type *iio_get_sw_trigger_type(char *name)
> +{
> +	struct iio_sw_trigger_type *t;
> +
> +	read_lock(&iio_trigger_types_lock);
> +	t = iio_find_sw_trigger_type(name, strlen(name));
> +	if (t && !try_module_get(t->owner))
> +		t = NULL;
> +	read_unlock(&iio_trigger_types_lock);
> +
> +	return t;
> +}
> +
> +struct iio_sw_trigger *iio_sw_trigger_create(char *type, char *name)
> +{
> +	struct iio_sw_trigger *t;
> +	struct iio_sw_trigger_type *tt;
I like the brief variable names (perfectly clear so not actually being
sarcastic ;))
> +
> +	tt = iio_get_sw_trigger_type(type);
> +	if (!tt) {
> +		pr_err("Invalid trigger type: %s\n", type);
> +		return ERR_PTR(-EINVAL);
> +	}
> +	t = tt->ops->probe(name);
> +	if (IS_ERR(t))
> +		goto out_module_put;
> +
> +	return t;
> +out_module_put:
> +	module_put(tt->owner);
> +	return t;
> +}
> +EXPORT_SYMBOL(iio_sw_trigger_create);
> +
> +void iio_sw_trigger_destroy(struct iio_sw_trigger *t)
> +{
> +	struct iio_sw_trigger_type *tt = t->trigger_type;
> +
> +	tt->ops->remove(t);
> +	module_put(tt->owner);
> +}
> +EXPORT_SYMBOL(iio_sw_trigger_destroy);
> diff --git a/include/linux/iio/sw_trigger.h b/include/linux/iio/sw_trigger.h
> new file mode 100644
> index 0000000..2e6659b
> --- /dev/null
> +++ b/include/linux/iio/sw_trigger.h
> @@ -0,0 +1,50 @@
> +#ifndef __IIO_SW_TRIGGER
> +#define __IIO_SW_TRIGGER
> +
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/iio/iio.h>
> +#include <linux/configfs.h>
> +
> +#define module_iio_sw_trigger_driver(__iio_sw_trigger_type) \
> +	module_driver(__iio_sw_trigger_type, iio_register_sw_trigger_type, \
> +		      iio_unregister_sw_trigger_type)
> +
> +struct iio_sw_trigger_ops;
> +
> +struct iio_sw_trigger_type {
> +	char *name;
> +	struct module *owner;
> +	struct iio_sw_trigger_ops *ops;
> +	struct list_head list;
> +};
> +
> +struct iio_sw_trigger {
> +	struct iio_trigger *trigger;
> +	struct iio_sw_trigger_type *trigger_type;
> +#ifdef CONFIG_CONFIGFS_FS
> +	struct config_group group;
> +#endif
> +};
> +
> +struct iio_sw_trigger_ops {
> +	struct iio_sw_trigger* (*probe)(const char *);
> +	int (*remove)(struct iio_sw_trigger *);
> +};
> +
> +int iio_register_sw_trigger_type(struct iio_sw_trigger_type *);
> +int iio_unregister_sw_trigger_type(struct iio_sw_trigger_type *);
> +
> +struct iio_sw_trigger *iio_sw_trigger_create(char *, char *);
> +void iio_sw_trigger_destroy(struct iio_sw_trigger *);
> +
> +#ifdef CONFIG_CONFIGFS_FS
> +static inline
> +struct iio_sw_trigger *to_iio_sw_trigger(struct config_item *item)
> +{
> +	return container_of(to_config_group(item), struct iio_sw_trigger,
> +			    group);
> +}
> +#endif
> +
> +#endif /* __IIO_SW_TRIGGER */
>