Date:	Sun, 26 Apr 2015 22:32:33 +0300
From:	Daniel Baluta <daniel.baluta@...el.com>
To:	Jonathan Cameron <jic23@...nel.org>
Cc:	Daniel Baluta <daniel.baluta@...el.com>,
	Joel Becker <jlbec@...lplan.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Hartmut Knaack <knaack.h@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"octavian.purdila@...el.com" <octavian.purdila@...el.com>,
	Paul Bolle <pebolle@...cali.nl>, patrick.porlan@...el.com,
	adriana.reus@...el.com, constantin.musca@...el.com,
	marten@...uitiveaerial.com
Subject: Re: [PATCH v4 1/4] iio: core: Introduce IIO software triggers

On Sun, Apr 26, 2015 at 10:21 PM, Jonathan Cameron <jic23@...nel.org> wrote:
> 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@...el.com>
> Looks sensible.
> My only real question is if the rwlock is justified (vs a mutex).

Hmm, a given iio_trigger_type list element is mostly read. Also, borrowed
the code from file systems core implementation.

http://lxr.linux.no/linux+v3.19.1/fs/filesystems.c#L33

Anyhow, there is no problem to use 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...

I see your point. Could change the code to use a mutex.

>> +
>> +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).

I see, we can do this later. Anyhow, I'm not convinced that EAGAIN is a good
value here. We just want to inform the user that the module registering this
trigger type is already loaded.

Like here:

http://lxr.linux.no/linux+v3.19.1/fs/filesystems.c#L78


>> +     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 */
>>
>
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