linux-kernel - Re: [PATCH 2/2] platform/chrome: cros_kbd_led_backlight: Remove obsolete commands (EC_CMD_PWM_*_KEYBOARD

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Date: Mon, 25 Mar 2024 11:45:13 -0700
From: Brian Norris <briannorris@...omium.org>
To: Stephen Horvath <s.horvath@...look.com.au>
Cc: Lee Jones <lee@...nel.org>, Benson Leung <bleung@...omium.org>, 
	Guenter Roeck <groeck@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>, 
	chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] platform/chrome: cros_kbd_led_backlight: Remove
 obsolete commands (EC_CMD_PWM_*_KEYBOARD_BACKLIGHT)

On Fri, Mar 22, 2024 at 3:34 AM Stephen Horvath
<s.horvath@...look.com.au> wrote:
>
> EC_CMD_PWM_GET_KEYBOARD_BACKLIGHT and EC_CMD_PWM_SET_KEYBOARD_BACKLIGHT
> are marked as obsolete in `cros_ec_commands.h`, this patch removes the
> usage of these commands from the driver.

Just because the EC firmware repository marks these as obsolete (and
yes, we copy that header mostly as-is into the kernel repository ...
but it's still a firmware header) doesn't mean it's truly ready to be
removed. I believe the intention is to direct *firmware* developers
not to use them -- any new developments should be using the new
commands.

>From a kernel perspective, we could still be supporting old firmware
on old devices, and so we may want/need to continue to support these
commands.

I don't know off the top of my head which firmware branches support
which commands, on devices that have such keyboard backlights. (The
Chromium EC repository is open source though, with various firmware-*
branches still around, so this information is available.) But without
a better explanation as to why these are truly ready to be removed,
I'll say "NAK."

Brian