Re: [PATCH 1/7] pwm: Add pwm core driver

[Lars-Peter Clausen <lars@metafoo.de>]

Arun Murthy wrote:
> The existing pwm based led and backlight driver makes use of the
> pwm(include/linux/pwm.h). So all the board specific pwm drivers will
> be exposing the same set of function name as in include/linux/pwm.h.
> As a result build fails.
> 
> In order to overcome this issue all the pwm drivers must register to
> some core pwm driver with function pointers for pwm operations (i.e
> pwm_config, pwm_enable, pwm_disable).
> 
> The clients of pwm device will have to call pwm_request, wherein
> they will get the pointer to struct pwm_ops. This structure include
> function pointers for pwm_config, pwm_enable and pwm_disable.
> 
> Signed-off-by: Arun Murthy <arun.murthy@stericsson.com>
> Acked-by: Linus Walleij <linus.walleij@stericsson.com>
> ---
>  drivers/Kconfig        |    2 +
>  drivers/Makefile       |    1 +
>  drivers/pwm/Kconfig    |   16 ++++++
>  drivers/pwm/Makefile   |    1 +
>  drivers/pwm/pwm-core.c |  129 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pwm.h    |   12 ++++-
>  6 files changed, 160 insertions(+), 1 deletions(-)
>  create mode 100644 drivers/pwm/Kconfig
>  create mode 100644 drivers/pwm/Makefile
>  create mode 100644 drivers/pwm/pwm-core.c
> 
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index a2b902f..e042f27 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -111,4 +111,6 @@ source "drivers/xen/Kconfig"
>  source "drivers/staging/Kconfig"
>  
>  source "drivers/platform/Kconfig"
> +
> +source "drivers/pwm/Kconfig"
>  endmenu
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 4ca727d..0061ec4 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -116,3 +116,4 @@ obj-$(CONFIG_STAGING)		+= staging/
>  obj-y				+= platform/
>  obj-y				+= ieee802154/
>  obj-y				+= vbus/
> +obj-$(CONFIG_PWM_DEVICES)	+= pwm/
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> new file mode 100644
> index 0000000..5d10106
> --- /dev/null
> +++ b/drivers/pwm/Kconfig
> @@ -0,0 +1,16 @@
> +#
> +# PWM devices
> +#
> +
> +menuconfig PWM_DEVICES
> +	bool "PWM devices"
> +	default y
> +	---help---
> +	  Say Y here to get to see options for device drivers from various
> +	  different categories. This option alone does not add any kernel code.
> +
> +	  If you say N, all options in this submenu will be skipped and disabled.
> +

Shouldn't PWM_DEVICES select HAVE_PWM?

> +if PWM_DEVICES
> +
> +endif # PWM_DEVICES
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> new file mode 100644
> index 0000000..552f969
> --- /dev/null
> +++ b/drivers/pwm/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_PWM_DEVICES)	+= pwm-core.o
> diff --git a/drivers/pwm/pwm-core.c b/drivers/pwm/pwm-core.c
> new file mode 100644
> index 0000000..b84027a
> --- /dev/null
> +++ b/drivers/pwm/pwm-core.c
> @@ -0,0 +1,129 @@
> +/*
> + * Copyright (C) ST-Ericsson SA 2010
> + *
> + * License Terms: GNU General Public License v2
> + * Author: Arun R Murthy <arun.murthy@stericsson.com>
> + */
> +#include <linux/init.h>
> +#include <linux/device.h>
> +#include <linux/slab.h>
> +#include <linux/rwsem.h>
> +#include <linux/err.h>
> +#include <linux/pwm.h>
> +
> +struct pwm_device {
> +	struct pwm_ops *pops;
> +	int pwm_id;
> +};
> +
> +struct pwm_dev_info {
> +	struct pwm_device *pwm_dev;
> +	struct list_head list;
> +};
> +static struct pwm_dev_info *di;

Why not embed the list head into pwm_device. That would certainly make
pwm_device_unregister much simpler.

> +
> +DECLARE_RWSEM(pwm_list_lock);
> +
> +void __deprecated pwm_free(struct pwm_device *pwm)
> +{
> +}
> +
> +int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
> +{
> +	return pwm->pops->pwm_config(pwm, duty_ns, period_ns);
> +}
> +EXPORT_SYMBOL(pwm_config);
> +
> +int pwm_enable(struct pwm_device *pwm)
> +{
> +	return pwm->pops->pwm_enable(pwm);
> +}
> +EXPORT_SYMBOL(pwm_enable);
> +
> +void pwm_disable(struct pwm_device *pwm)
> +{
> +	pwm->pops->pwm_disable(pwm);
> +}
> +EXPORT_SYMBOL(pwm_disable);
> +
> +int pwm_device_register(struct pwm_device *pwm_dev)
> +{
> +	struct pwm_dev_info *pwm;
> +
> +	down_write(&pwm_list_lock);
> +	pwm = kzalloc(sizeof(struct pwm_dev_info), GFP_KERNEL);
> +	if (!pwm) {
> +		up_write(&pwm_list_lock);
> +		return -ENOMEM;
> +	}
> +	pwm->pwm_dev = pwm_dev;
> +	list_add_tail(&pwm->list, &di->list);
> +	up_write(&pwm_list_lock);
> +

I guess you only need to lock the list when accessing the list and adding the new
pwm_dev.

> +	return 0;
> +}
> +EXPORT_SYMBOL(pwm_device_register);
> +
> +int pwm_device_unregister(struct pwm_device *pwm_dev)
> +{
> +	struct pwm_dev_info *tmp;
> +	struct list_head *pos, *tmp_lst;
> +
> +	down_write(&pwm_list_lock);
> +	list_for_each_safe(pos, tmp_lst, &di->list) {
> +		tmp = list_entry(pos, struct pwm_dev_info, list);
> +		if (tmp->pwm_dev == pwm_dev) {
> +			list_del(pos);
> +			kfree(tmp);
> +			up_write(&pwm_list_lock);
> +			return 0;
> +		}
> +	}
> +	up_write(&pwm_list_lock);
> +	return -ENOENT;
> +}
> +EXPORT_SYMBOL(pwm_device_unregister);
> +
> +struct pwm_device *pwm_request(int pwm_id, const char *name)
> +{
> +	struct pwm_dev_info *pwm;
> +	struct list_head *pos;
> +
> +	down_read(&pwm_list_lock);
> +	list_for_each(pos, &di->list) {
> +		pwm = list_entry(pos, struct pwm_dev_info, list);
> +		if ((!strcmp(pwm->pwm_dev->pops->name, name)) &&
> +				(pwm->pwm_dev->pwm_id == pwm_id)) {
> +			up_read(&pwm_list_lock);
> +			return pwm->pwm_dev;
> +		}
> +	}
> +	up_read(&pwm_list_lock);
> +	return ERR_PTR(-ENOENT);
> +}
> +EXPORT_SYMBOL(pwm_request);
> +
> +static int __init pwm_init(void)
> +{
> +	struct pwm_dev_info *pwm;
> +
> +	pwm = kzalloc(sizeof(struct pwm_dev_info), GFP_KERNEL);
> +	if (!pwm)
> +		return -ENOMEM;
> +	INIT_LIST_HEAD(&pwm->list);
> +	di = pwm;
> +	return 0;
> +}
> +
> +static void __exit pwm_exit(void)
> +{
> +	kfree(di);
> +}
> +
> +subsys_initcall(pwm_init);
> +module_exit(pwm_exit);
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR("Arun R Murthy");
> +MODULE_ALIAS("core:pwm");
> +MODULE_DESCRIPTION("Core pwm driver");
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index 7c77575..6e7da1f 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -3,6 +3,13 @@
>  
>  struct pwm_device;
>  
> +struct pwm_ops {
> +	int (*pwm_config)(struct pwm_device *pwm, int duty_ns, int period_ns);
> +	int (*pwm_enable)(struct pwm_device *pwm);
> +	int (*pwm_disable)(struct pwm_device *pwm);
> +	char *name;
> +};
> +

Shouldn't name be part of the pwm_device? That would allow the ops to be shared
between different devices.

>  /*
>   * pwm_request - request a PWM device
>   */
> @@ -11,7 +18,7 @@ struct pwm_device *pwm_request(int pwm_id, const char *label);
>  /*
>   * pwm_free - free a PWM device
>   */
> -void pwm_free(struct pwm_device *pwm);
> +void __deprecated pwm_free(struct pwm_device *pwm);
>  
>  /*
>   * pwm_config - change a PWM device configuration
> @@ -28,4 +35,7 @@ int pwm_enable(struct pwm_device *pwm);
>   */
>  void pwm_disable(struct pwm_device *pwm);
>  
> +int pwm_device_register(struct pwm_device *pwm_dev);
> +int pwm_device_unregister(struct pwm_device *pwm_dev);
> +
>  #endif /* __LINUX_PWM_H */

It might be also a good idea to add a device class for pwm devices.