linux-kernel - Re: [PATCH] Blacklist Dell Optiplex 320 from using the HPET

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Date:	Sat, 5 May 2007 19:24:14 +0200
From:	Andi Kleen <ak@...e.de>
To:	tglx@...utronix.de
Cc:	john stultz <johnstul@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Guilherme M. Schroeder" <guilherme@...tralinf.com.br>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Blacklist Dell Optiplex 320 from using the HPET


>  	if (!is_hpet_capable())
> @@ -278,6 +279,14 @@ int __init hpet_enable(void)
>  	/* Start the counter */
>  	hpet_start_counter();
>  
> +	/* Verify whether hpet counter works */
> +	t1 = hpet_read();
> +	udelay(50);

Are you sure udelay is calibrated at this point? I didn't think so.
In fact it needs the external clocks and it's a chicken and egg problem.

It might be safer to use a long loop with io port accesses or similar.

-Andi


> +	if (t1 == hpet_read()) {
> +		printk(KERN_WARNING "HPET counter is defect\n");
> +		goto out_nohpet;
> +	}
> +
>  	/* Initialize and register HPET clocksource
>  	 *
>  	 * hpet period is in femto seconds per cycle
> 
> 
> 


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