Introduce a mechanism for drivers to extend the properties implemented by a power supply. Motivation ---------- Various drivers, mostly in platform/x86 extend the ACPI battery driver with additional sysfs attributes to implement more UAPIs than are exposed through ACPI by using various side-channels, like WMI, nonstandard ACPI or EC communication. While the created sysfs attributes look similar to the attributes provided by the powersupply core, there are various deficiencies: * They don't show up in uevent payload. * They can't be queried with the standard in-kernel APIs. * They don't work with triggers. * The extending driver has to reimplement all of the parsing, formatting and sysfs display logic. * Writing a extension driver is completely different from writing a normal power supply driver. * Properties can not be properly overriden. The proposed extension API avoids all of these issues. An extension is just a "struct power_supply_ext" with the same kind of callbacks as in a normal "struct power_supply_desc". The API is meant to be used via battery_hook_register(), the same way as the current extensions. For example my upcoming cros_ec charge control driver[0] saves 80 lines of code with this patchset. Contents -------- * Patch 1 and 2 are generic preparation patches, that probably make sense without this series. * Patch 3 implements the extension API itself. * Patch 4 implements a PoC locking scheme for the extension API. * Patch 5 adds extension support to test_power.c * Patch 6 converts the in-tree platform/x86/system76 driver to the extension API. Open issues ----------- * Newly registered properties will not show up in hwmon. To do that properly would require some changes in the hwmon core. As far as I know, no current driver would extend the hwmon properties anyways. * As this is only useful with the hooks of CONFIG_ACPI_BATTERY, should it also be gated behind this or another config? * Only one extension can be used at a time. So far this should be enough, having more would complicate the implementation. * Is an rw_semaphore acceptable? [0] https://lore.kernel.org/lkml/20240528-cros_ec-charge-control-v2-0-81fb27e1cff4@xxxxxxxxxxxxxx/ Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx> --- Thomas Weißschuh (6): power: supply: sysfs: use power_supply_property_is_writeable() power: supply: core: avoid iterating properties directly power: supply: core: implement extension API power: supply: core: add locking around extension access power: supply: test-power: implement a power supply extension platform/x86: system76: Use power_supply extension API drivers/platform/x86/system76_acpi.c | 83 +++++++++--------- drivers/power/supply/power_supply.h | 9 ++ drivers/power/supply/power_supply_core.c | 136 ++++++++++++++++++++++++++++-- drivers/power/supply/power_supply_hwmon.c | 48 +++++------ drivers/power/supply/power_supply_sysfs.c | 39 ++++++--- drivers/power/supply/test_power.c | 102 ++++++++++++++++++++++ include/linux/power_supply.h | 25 ++++++ 7 files changed, 357 insertions(+), 85 deletions(-) --- base-commit: 2df0193e62cf887f373995fb8a91068562784adc change-id: 20240602-power-supply-extensions-07d949f509d9 Best regards, -- Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
