[PATCH 3.0+] ath9k: Fix softlockup in AR9485(backported)

[Sujith Manoharan <c_manoha@xxxxxxxxxxxxxxxx>]

Mohammed Shafi Shajakhan wrote:
> From: Mohammed Shafi Shajakhan <mohammed@xxxxxxxxxxxxxxxx>
> 
> Please note this is the backported version for the linux
> stable tree, while the patch for wireless-testing tree
> http://permalink.gmane.org/gmane.linux.kernel.wireless.general/92608
> 
> steps to recreate:
> load latest ath9k driver with AR9485
> stop the network-manager and wpa_supplicant
> bring the interface up
> 
> 	Call Trace:
> 	[<ffffffffa0517490>] ? ath_hw_check+0xe0/0xe0 [ath9k]
> 	[<ffffffff812cd1e8>] __const_udelay+0x28/0x30
> 	[<ffffffffa03bae7a>] ar9003_get_pll_sqsum_dvc+0x4a/0x80 [ath9k_hw]
> 	[<ffffffffa05174eb>] ath_hw_pll_work+0x5b/0xe0 [ath9k]
> 	[<ffffffff810744fe>] process_one_work+0x11e/0x470
> 	[<ffffffff8107530f>] worker_thread+0x15f/0x360
> 	[<ffffffff810751b0>] ? manage_workers+0x230/0x230
> 	[<ffffffff81079af3>] kthread+0x93/0xa0
> 	[<ffffffff815fd3a4>] kernel_thread_helper+0x4/0x10
> 	[<ffffffff81079a60>] ? kthread_freezable_should_stop+0x70/0x70
> 	[<ffffffff815fd3a0>] ? gs_change+0x13/0x13
> 
> ensure that the PLL-WAR for AR9485/AR9340 is executed only if the STA is
> associated (or) IBSS/AP mode had started beaconing. Ideally this WAR
> is needed to recover from some rare beacon stuck during stress testing.
> Before the STA is associated/IBSS had started beaconing, PLL4(0x1618c)
> always seem to have zero even though we had configured PLL3(0x16188) to
> query about PLL's locking status. When we keep on polling infinitely PLL4's
> 8th bit(ie check for PLL locking measurements is done), machine hangs
> due to softlockup.

While I do agree that this patch fixes the regression for AR9485 chipsets,
the code in ar9003_get_pll_sqsum_dvc needs to be fixed, i.e., to not loop
till the end of time and have a timeout.

Sujith
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