linux-kernel - Re: [PATCH] dell-laptop: Fix backlight detection

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Date:   Sun, 8 Jul 2018 17:09:14 +0200
From:   Pali Rohár <pali.rohar@...il.com>
To:     Damien Thébault <damien@...o.net>
Cc:     Matthew Garrett <mjg59@...f.ucam.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Mario Limonciello <mario.limonciello@...l.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dell-laptop: Fix backlight detection

On Sunday 08 July 2018 17:02:20 Damien Thébault wrote:
> Fix return code check for "max brightness" ACPI call.
> 
> The dell laptop ACPI video brightness control is not present on dell
> laptops anymore, but was present in older kernel versions.
> 
> The code that checks the return value is incorrect since the SMM
> refactoring.
> 
> The old code was:
>   if (buffer->output[0] == 0)
> 
> Which was changed to:
>   ret = dell_send_request(...)
>   if (ret)
> 
> However, dell_send_request() will return 0 if buffer->output[0] == 0,
> so we must change the check to:
>   if (ret == 0)

You are right, dell_send_request() return non-zero value on error.

> This issue was found on a Dell M4800 laptop, and the fix tested on it
> as well.
> 
> Fixes: 549b4930f057 ("dell-smbios: Introduce dispatcher for SMM calls")
> Signed-off-by: Damien Thébault <damien@...o.net>
> Tested-by: Damien Thébault <damien@...o.net>
> ---
>  drivers/platform/x86/dell-laptop.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/x86/dell-laptop.c
> b/drivers/platform/x86/dell-laptop.c index f1fa8612db40..06978c14c83b
> 100644 --- a/drivers/platform/x86/dell-laptop.c
> +++ b/drivers/platform/x86/dell-laptop.c
> @@ -2185,7 +2185,7 @@ static int __init dell_init(void)
>  		dell_fill_request(&buffer, token->location, 0, 0, 0);
>  		ret = dell_send_request(&buffer,
>  					CLASS_TOKEN_READ,
> SELECT_TOKEN_AC);
> -		if (ret)
> +		if (ret == 0)
>  			max_intensity = buffer.output[3];
>  	}
>  

Reviewed-by: Pali Rohár <pali.rohar@...il.com>

-- 
Pali Rohár
pali.rohar@...il.com

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