Date: Fri, 10 Oct 2008 14:34:57 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Elias Oltmanns <eo@nebensachen.de>
cc: Jiri Slaby <jirislaby@gmail.com>, linux-wireless@vger.kernel.org
Subject: Re: ath5k: kernel timing screwed - due to unserialised register
 access?
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On Fri, 10 Oct 2008, Elias Oltmanns wrote:
> That printk() has not been hit, I'm afraid. The output of
> sysrq_timer_list_show() looks much the same but there is no message
> about softirqs. Just for the record, I've switched to 2.6.27 because I'm
> debugging something else at the same time, but it doesn't make any
> difference.
> 
> Now, here is another question: There are various snippets like the
> following in the ath5k driver:
> 
> 	/* Wait until the noise floor is calibrated and read the value */
> 	for (i = 20; i > 0; i--) {
> 		mdelay(1);

Uurgh. That's broken. mdelay sleeps so this should not be called in
softirq context.

> 		noise_floor = ath5k_hw_reg_read(ah, AR5K_PHY_NF);
> 		noise_floor = AR5K_PHY_NF_RVAL(noise_floor);
> 		if (noise_floor & AR5K_PHY_NF_ACTIVE) {
> 			noise_floor = AR5K_PHY_NF_AVAL(noise_floor);
> 
> 			if (noise_floor <= AR5K_TUNE_NOISE_FLOOR)
> 				break;
> 		}
> 	}
> 
> This particular one is in
> drivers/net/wireless/ath5k/phy.c:ath5k_hw_noise_floor_calibration()
> which is called from ath5k_calibrate(), the callback executed every ten
> seconds in softirq context. Could this have anything to do with our

That makes sense. The timer expires early events are multiples of 10s
apart.

Thanks,

	tglx