linux-kernel - Re: [PATCH] platform/chrome: cros_kbd_led_backlight: enable probing through EC_FEATURE_PWM

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Date: Thu, 9 May 2024 12:25:01 +0800
From: Tzung-Bi Shih <tzungbi@...nel.org>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Mario Limonciello <mario.limonciello@....com>,
	Lee Jones <lee@...nel.org>, Benson Leung <bleung@...omium.org>,
	Guenter Roeck <groeck@...omium.org>,
	chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org,
	Dustin Howett <dustin@...ett.net>
Subject: Re: [PATCH] platform/chrome: cros_kbd_led_backlight: enable probing
 through EC_FEATURE_PWM_KEYB

On Mon, May 06, 2024 at 07:38:09PM +0200, Thomas Weißschuh wrote:
> On 2024-05-05 08:42:21+0000, Mario Limonciello wrote:
> > On 5/5/2024 04:41, Thomas Weißschuh wrote:
> > > The ChromeOS EC used in Framework laptops supports the standard cros
> > > keyboard backlight protocol.
> > > However the firmware on these laptops don't implement the ACPI ID
> > > GOOG0002 that is recognized by cros_kbd_led_backlight and they also
> > > don't use device tree.

If implementing ACPI ID GOOG0002 is not an option, how about adding a new ACPI
ID?  For the new ACPI ID, it can use EC PWM for setting the brightness.

> > Something I'd wonder is if the GOOG0002 ACPI ID can go away entirely with
> > this type of change.  Presumably the Chromebooks with ChromeOS EC /also/
> > advertise EC_FEATURE_PWM_KEYB.
> 
> Sounds good to me in general. It would make the code cleaner.
> 
> But I have no idea how CrOS kernels are set up in general.
> If they are not using CONFIG_MFD_CROS_EC_DEV for some reason that
> wouldn't work.
> 
> If the CrOS folks agree with that aproach I'll be happy to implement it.

I would say NO as some existing devices (with legacy firmware and kernel) may
rely on it.