linux-kernel - Re: [PATCH] toshiba_acpi: Fix blank screen at boot if transflective backlight is supported

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Message-ID: <20151120231632.GC7413@malice.jf.intel.com>
Date:	Fri, 20 Nov 2015 15:16:32 -0800
From:	Darren Hart <dvhart@...radead.org>
To:	Azael Avalos <coproscefalo@...il.com>
Cc:	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	Fabian Koester <fabian.koester@...ngnow.com>
Subject: Re: [PATCH] toshiba_acpi: Fix blank screen at boot if transflective
 backlight is supported

On Sun, Nov 15, 2015 at 08:32:47PM -0700, Azael Avalos wrote:
> If transflective backlight is supported and the brightness is zero
> (lowest brightness level), the set_lcd_brightness function will activate
> the transflective backlight, making the LCD appear to be turned off.
> 
> This patch fixes the issue by incrementing the brightness level, and
> by doing so, avoiding the activation of the tranflective backlight.

So... I'm not sure this is a bug or even wrong behavior. The lowest setting on
my Thinkpad Yoga 12 is also "off" in Linux. Same is true for my Mac Book Pro (in
Mac OS X).

>From what I can tell, what this patch does is merely disable the lowest setting.

What is it about this behavior that is considered to be wrong?

> 
> Cc: <stable@...r.kernel.org> # 4.3+
> Reported-and-tested-by: Fabian Koester <fabian.koester@...ngnow.com>
> Signed-off-by: Azael Avalos <coproscefalo@...il.com>
> ---
>  drivers/platform/x86/toshiba_acpi.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/platform/x86/toshiba_acpi.c b/drivers/platform/x86/toshiba_acpi.c
> index 2ca3f91..b6a7dc9 100644
> --- a/drivers/platform/x86/toshiba_acpi.c
> +++ b/drivers/platform/x86/toshiba_acpi.c
> @@ -2634,6 +2634,14 @@ static int toshiba_acpi_setup_backlight(struct toshiba_acpi_dev *dev)
>  	brightness = __get_lcd_brightness(dev);
>  	if (brightness < 0)
>  		return 0;
> +	/*
> +	 * If transflective backlight is supported and the brightness is zero
> +	 * (lowest brightness level), the set_lcd_brightness function will
> +	 * activate the transflective backlight, making the LCD appear to be
> +	 * turned off, simply increment the brightness level to avoid that.
> +	 */
> +	if (dev->tr_backlight_supported && brightness == 0)
> +		brightness++;
>  	ret = set_lcd_brightness(dev, brightness);
>  	if (ret) {
>  		pr_debug("Backlight method is read-only, disabling backlight support\n");
> -- 
> 2.6.2
> 
> 

-- 
Darren Hart
Intel Open Source Technology Center
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