linux-kernel - Re: [v2 3/4] platform: (TS-5500) add LED support

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Date:	Tue, 30 Aug 2011 15:04:00 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
CC:	Mark Brown <broonie@...nsource.wolfsonmicro.com>, x86@...nel.org,
	Jonas Fonseca <jonas.fonseca@...oirfairelinux.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [v2 3/4] platform: (TS-5500) add LED support

On 08/30/2011 02:56 PM, Vivien Didelot wrote:
>>
> I wrote the led_set function like:
> 
>   static void ts5500_led_set(struct led_classdev *led_cdev,
>                              enum led_brightness value)
>   {
>           struct ts5500_led *led = container_of(led_cdev,
>                                                 struct ts5500_led,
>                                                 cdev);
>           mutex_lock(&led->lock);
>           led->new_brightness = (value == LED_OFF) ? LED_OFF : LED_FULL;
>           outb(value, led->ioaddr);
>           mutex_unlock(&led->lock);
>   }
> 
> I guess the wrong value could be read if we get preempted just before
> the outb() call, am I wrong?
> 

And what happens if we do?

P.S. Your canonicalization of the value doesn't extend to outb().

	-hpa
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