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Message-ID: <41964782-222c-45fa-846e-3656eff5b3a9@gmx.de>
Date: Fri, 7 Jun 2024 01:10:02 +0200
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Subject: Re: [PATCH RFC 0/6] power: supply: extension API
To: =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= <linux@weissschuh.net>,
 Sebastian Reichel <sre@kernel.org>, Jeremy Soller <jeremy@system76.com>,
 System76 Product Development <productdev@system76.com>,
 Hans de Goede <hdegoede@redhat.com>,
 =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
 platform-driver-x86@vger.kernel.org
References: <20240606-power-supply-extensions-v1-0-b45669290bdc@weissschuh.net>
Content-Language: en-US
From: Armin Wolf <W_Armin@gmx.de>
In-Reply-To: <20240606-power-supply-extensions-v1-0-b45669290bdc@weissschuh.net>
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Am 06.06.24 um 16:50 schrieb Thomas Wei=C3=9Fschuh:

> 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-v2-0-81=
fb27e1cff4@weissschuh.net/

Nice, i love this proposal!

I agree that the hwmon update functionality will need some changes in the =
hwmon core to work,
but there would be at least one driver benefiting from this (dell-wmi-ddv)=
. Maybe we can add
support for this at a later point in time.

The possibility of registering multiple power supply extensions on a singl=
e power supply will
be necessary to support battery charge control on Dell notebooks in the fu=
ture. This is because
there will be two drivers on Dell notebooks which register battery extensi=
ons: dell-wmi-ddv and
dell-laptop (when support for battery charge control is supported someday)=
.

How difficult would it be to support such scenarios? If its very difficult=
, then maybe we can implement
this later when the need arises.

Thanks,
Armin Wolf

> Signed-off-by: Thomas Wei=C3=9Fschuh <linux@weissschuh.net>
> ---
> Thomas Wei=C3=9Fschuh (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,