linux-kernel - Re: [PATCH v3 0/6] platform/x86: firmware_attributes

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Message-Id: <DASQQCLO08Q6.WGADUXY300N0@gmail.com>
Date: Sun, 22 Jun 2025 00:27:06 -0300
From: "Kurt Borja" <kuurtb@...il.com>
To: "Derek J. Clark" <derekjohn.clark@...il.com>, "Hans de Goede"
 <hdegoede@...hat.com>, Ilpo Järvinen
 <ilpo.jarvinen@...ux.intel.com>, Thomas Weißschuh
 <linux@...ssschuh.net>, "Joshua Grisham" <josh@...huagrisham.com>, "Mark
 Pearson" <mpearson-lenovo@...ebb.ca>, "Armin Wolf" <W_Armin@....de>, "Mario
 Limonciello" <mario.limonciello@....com>
Cc: "Antheas Kapenekakis" <lkml@...heas.dev>, "Prasanth Ksr"
 <prasanth.ksr@...l.com>, "Jorge Lopez" <jorge.lopez2@...com>,
 <platform-driver-x86@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <Dell.Client.Kernel@...l.com>
Subject: Re: [PATCH v3 0/6] platform/x86: firmware_attributes_class: Add a
 high level API

On Sun Jun 22, 2025 at 12:01 AM -03, Derek J. Clark wrote:
>
>
> On June 21, 2025 5:04:03 PM PDT, Kurt Borja <kuurtb@...il.com> wrote:
>>Hi all,
>>
>>I apologize for taking so long. I've been a bit busy these last few
>>weeks.
>>
>>After my discussion with Joshua on v2, I realized the API I made was not
>>ergonomic at all and it didn't exactly respond to driver needs. In this
>>version I tried a completely different approach and IMO it's much much
>>better now.
>>
>>First of all I adopted standard sysfs terminology for everything. A
>>"firmware attribute" is just an attribute_group under the attributes/
>>directory so everything related to this concept is just called "group"
>>now. Everything refered as properties in the previous patch are now just
>>plain "attributes".
>>
>>This new API revolves around the `fwat_{bool,enum,int,str}_data`
>>structs. These hold all the metadata a "firmware_attribute" of that
>>given type needs.
>>
>>These structs also hold `read` and `write` callbacks for the
>>current_value attribute, because obviously that value is always dynamic.
>>However the rest of attributes (default_value, display_name, min, max,
>>etc) are constant.
>
> Hi Kurt,
>
> In the lenovo-wmi drivers the min/max for multiple attributes are actually dynamic based on if power is AC connected or on battery. Looking at patch 2 I might be able to do some pointer manipulation with the attribute's "data" member for those events to make this work, but it would be a lot easier if there was a simple way for me to call my own functions here instead. Perhaps a function pointer could be used to override the default method here? 

Hi Derek,

All attributes in a given group have the same show method. Maybe we can
let users override this with their own show method, i.e. Add a

	ssize_t (*attr_show)(struct device *dev, const struct fwat_attribute *attr, const char *buf)

to struct fwat_group_data. That should be fairly simple to implement.

Did you have another solution in mind?

-- 
 ~ Kurt