linux-kernel - Re: [PATCH v2] platform/x86: dell-laptop: Fix bogus keyboard backlight sysfs interface

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Date:   Mon, 19 Jun 2017 09:57:42 +0200
From:   Pali Rohár <pali.rohar@...il.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     andy@...radead.org, mjg59@...f.ucam.org, dvhart@...radead.org,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] platform/x86: dell-laptop: Fix bogus keyboard
 backlight sysfs interface

On Monday 19 June 2017 15:36:29 Kai-Heng Feng wrote:
> Dell Latitude 3160 does not have keyboard backlight, but there is a
> sysfs interface for it, which does nothing at all.
> 
> KBD_LED_ON_TOKEN is the only token can be found. Since it doesn't have

*ON* really?

> KBD_LED_OFF_TOKEN or KBD_LED_AUTO_*_TOKEN, it should be safe to assume it
> does not support keyboard backlight.
> 
> Models which do not use SMBIOS to control keyboard backlight, also have
> this issue. Brightness level is 0 on these models. Verified on Dell
> Inspiron 3565.
> 
> Reports keyboard backlight is supported only when tokens other than
> KBD_LED_ON_TOKEN can be found, or brightness level is not 0.
> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
> 
> v2:
> The only token can be found is actually KBD_LED_ON_TOKEN, which is BIT(5),
> instead of KBD_LED_OFF_TOKEN. Change commit log accordingly.
> 
> Use token bit to make the intention more clear.
> Also consider kbd_mode_levels_count and kbd_info.levels, suggested by
> Pali Rohár.
> 
> Use XOR to simplify the bitmask comparison, suggested by
> Andy Shevchenko.
> 
>  drivers/platform/x86/dell-laptop.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/x86/dell-laptop.c b/drivers/platform/x86/dell-laptop.c
> index ec202094bd50..4b21fc982cb0 100644
> --- a/drivers/platform/x86/dell-laptop.c
> +++ b/drivers/platform/x86/dell-laptop.c
> @@ -1148,6 +1148,15 @@ static const int kbd_tokens[] = {
>  	KBD_LED_ON_TOKEN,
>  };
>  
> +enum kbd_led_token_bit {
> +	KBD_LED_TOKEN_BIT_OFF = 0,
> +	KBD_LED_TOKEN_BIT_AUTO_25,
> +	KBD_LED_TOKEN_BIT_AUTO_50,
> +	KBD_LED_TOKEN_BIT_AUTO_75,
> +	KBD_LED_TOKEN_BIT_AUTO_100,
> +	KBD_LED_TOKEN_BIT_ON,
> +};
> +
>  static u16 kbd_token_bits;
>  
>  static struct kbd_info kbd_info;
> @@ -1510,7 +1519,12 @@ static void kbd_init(void)
>  	ret = kbd_init_info();
>  	kbd_init_tokens();
>  
> -	if (kbd_token_bits != 0 || ret == 0)
> +	/*
> +	 * If brightness level is 0, or KBD_LED_ON_TOKEN is the only token,
> +	 * consider there is no keyboard backlight.
> +	 */
> +	if ((ret == 0 && (kbd_info.levels || kbd_mode_levels_count)) ||
> +	    kbd_token_bits ^ BIT(KBD_LED_TOKEN_BIT_ON))

So in case there would be only *OFF* token then interface is exported
too... This does not seems to be good idea.

If there is machine for which firmware provides only *ON* token, then I
think we should presence for at least two tokens.

And similarly kbd_mode_levels_count needs to be checked that is at least
two (as "off" is in count).

>  		kbd_led_present = true;
>  }
>  

-- 
Pali Rohár
pali.rohar@...il.com