Re: [PATCH v6 4/4] power: supply: core: add UAPI to discover currently used extensions

["Thomas Weißschuh" <linux@weissschuh.net>]

Hi Nathan,

On 2024-12-18 12:52:29-0700, Nathan Chancellor wrote:
> On Wed, Dec 11, 2024 at 08:57:58PM +0100, Thomas Weißschuh wrote:
> > Userspace wants to now about the used power supply extensions,
> > for example to handle a device extended by a certain extension
> > differently or to discover information about the extending device.
> > 
> > Add a sysfs directory to the power supply device.
> > This directory contains links which are named after the used extension
> > and point to the device implementing that extension.
> > 
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > ---
> >  Documentation/ABI/testing/sysfs-class-power |  9 +++++++++
> >  drivers/power/supply/cros_charge-control.c  |  5 ++++-
> >  drivers/power/supply/power_supply.h         |  2 ++
> >  drivers/power/supply/power_supply_core.c    | 19 +++++++++++++++++--
> >  drivers/power/supply/power_supply_sysfs.c   | 10 ++++++++++
> >  drivers/power/supply/test_power.c           |  4 +++-
> >  include/linux/power_supply.h                |  2 ++
> >  7 files changed, 47 insertions(+), 4 deletions(-)
> ...
> > diff --git a/drivers/power/supply/power_supply.h b/drivers/power/supply/power_supply.h
> > index 531785516d2ac31f9a7f73a58e15e64cb81820ed..9ed749cd09369f0f13017847687509736b30aae8 100644
> > --- a/drivers/power/supply/power_supply.h
> > +++ b/drivers/power/supply/power_supply.h
> > @@ -39,6 +40,7 @@ struct power_supply_ext_registration {
> >  
> >  extern void __init power_supply_init_attrs(void);
> >  extern int power_supply_uevent(const struct device *dev, struct kobj_uevent_env *env);
> > +extern const struct attribute_group power_supply_extension_group;
> >  extern const struct attribute_group *power_supply_attr_groups[];
> >  
> >  #else
> > diff --git a/drivers/power/supply/power_supply_core.c b/drivers/power/supply/power_supply_core.c
> > index bc22edbd0e6a02c27500132075f5c98d814a7330..5142fbd580ee3d629a2aae7d0b9bcd5709162129 100644
> > --- a/drivers/power/supply/power_supply_core.c
> > +++ b/drivers/power/supply/power_supply_core.c
> > @@ -1346,17 +1346,21 @@ static int power_supply_update_sysfs_and_hwmon(struct power_supply *psy)
> >  }
> >  
> >  int power_supply_register_extension(struct power_supply *psy, const struct power_supply_ext *ext,
> > -				    void *data)
> > +				    struct device *dev, void *data)
> >  {
> >  	struct power_supply_ext_registration *reg;
> >  	size_t i;
> >  	int ret;
> >  
> > -	if (!psy || !ext || !ext->properties || !ext->num_properties)
> > +	if (!psy || !dev || !ext || !ext->name || !ext->properties || !ext->num_properties)
> >  		return -EINVAL;
> >  
> >  	guard(rwsem_write)(&psy->extensions_sem);
> >  
> > +	power_supply_for_each_extension(reg, psy)
> > +		if (strcmp(ext->name, reg->ext->name) == 0)
> > +			return -EEXIST;
> > +
> >  	for (i = 0; i < ext->num_properties; i++)
> >  		if (power_supply_has_property(psy, ext->properties[i]))
> >  			return -EEXIST;
> > @@ -1366,9 +1370,15 @@ int power_supply_register_extension(struct power_supply *psy, const struct power
> >  		return -ENOMEM;
> >  
> >  	reg->ext = ext;
> > +	reg->dev = dev;
> >  	reg->data = data;
> >  	list_add(&reg->list_head, &psy->extensions);
> >  
> > +	ret = sysfs_add_link_to_group(&psy->dev.kobj, power_supply_extension_group.name,
> > +				      &dev->kobj, ext->name);
> > +	if (ret)
> > +		goto sysfs_link_failed;
> > +
> >  	ret = power_supply_update_sysfs_and_hwmon(psy);
> >  	if (ret)
> >  		goto sysfs_hwmon_failed;
> > @@ -1376,6 +1386,8 @@ int power_supply_register_extension(struct power_supply *psy, const struct power
> >  	return 0;
> >  
> >  sysfs_hwmon_failed:
> > +	sysfs_remove_link_from_group(&psy->dev.kobj, power_supply_extension_group.name, ext->name);
> > +sysfs_link_failed:
> >  	list_del(&reg->list_head);
> >  	kfree(reg);
> >  	return ret;
> > @@ -1392,6 +1404,9 @@ void power_supply_unregister_extension(struct power_supply *psy, const struct po
> >  		if (reg->ext == ext) {
> >  			list_del(&reg->list_head);
> >  			kfree(reg);
> > +			sysfs_remove_link_from_group(&psy->dev.kobj,
> > +						     power_supply_extension_group.name,
> > +						     reg->ext->name);
> >  			power_supply_update_sysfs_and_hwmon(psy);
> >  			return;
> >  		}
> 
> I am seeing a build failure in certain configurations because
> power_supply_extension_group is only declared under a CONFIG_SYSFS ifdef
> but this code can be built without CONFIG_SYSFS.

Thanks for the report.

>   $ echo 'CONFIG_EXPERT=y
>   CONFIG_SYSFS=n' >allno.config
> 
>   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux- KCONFIG_ALLCONFIG=1 mrproper allnoconfig drivers/power/supply/power_supply_core.o
>   drivers/power/supply/power_supply_core.c: In function 'power_supply_register_extension':
>   drivers/power/supply/power_supply_core.c:1389:55: error: 'power_supply_extension_group' undeclared (first use in this function); did you mean 'power_supply_attr_groups'?
>    1389 |         ret = sysfs_add_link_to_group(&psy->dev.kobj, power_supply_extension_group.name,
>         |                                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>         |                                                       power_supply_attr_groups
>   drivers/power/supply/power_supply_core.c:1389:55: note: each undeclared identifier is reported only once for each function it appears in
>   drivers/power/supply/power_supply_core.c: In function 'power_supply_unregister_extension':
>   drivers/power/supply/power_supply_core.c:1419:54: error: 'power_supply_extension_group' undeclared (first use in this function); did you mean 'power_supply_attr_groups'?
>    1419 |                                                      power_supply_extension_group.name,
>         |                                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>         |                                                      power_supply_attr_groups

The reproducer doesn't actually enable CONFIG_POWER_SUPPLY, when I use it
I get a whole array of errors.

> Should the declaration be moved out from the ifdef or is there some
> other solution I am not seeing?

This, inline constants or a #define.

Sebastian, do you want me to send a patch?

> Cheers,
> Nathan
> 
> diff --git a/drivers/power/supply/power_supply.h b/drivers/power/supply/power_supply.h
> index 9ed749cd0936..6fc9939145fc 100644
> --- a/drivers/power/supply/power_supply.h
> +++ b/drivers/power/supply/power_supply.h
> @@ -40,7 +40,6 @@ struct power_supply_ext_registration {
>  
>  extern void __init power_supply_init_attrs(void);
>  extern int power_supply_uevent(const struct device *dev, struct kobj_uevent_env *env);
> -extern const struct attribute_group power_supply_extension_group;
>  extern const struct attribute_group *power_supply_attr_groups[];
>  
>  #else
> @@ -51,6 +50,8 @@ static inline void power_supply_init_attrs(void) {}
>  
>  #endif /* CONFIG_SYSFS */
>  
> +extern const struct attribute_group power_supply_extension_group;
> +
>  #ifdef CONFIG_LEDS_TRIGGERS
>  
>  extern void power_supply_update_leds(struct power_supply *psy);