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

From: Nathan Chancellor
Date: Wed Dec 18 2024 - 14:52:43 EST

Hi Thomas,

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@xxxxxxxxxxxxxx>
> ---
> 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.

$ 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

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

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);