[Regression, 3.2-rc1] ath9k broken on AR928X (was: Re: Linux 3.2-rc3 - just in time for Thanksgiving)

[Rafael J. Wysocki]

On Friday, November 25, 2011, Rafael J. Wysocki wrote:
> On Thursday, November 24, 2011, Linus Torvalds wrote:
> > Hey, since most of the US will be in a food-induced coma tomorrow, I
> > just *know* that doing a new release candidate is a good idea.
> > 
> > One quarter arch updates, two quarters drivers, and one quarter random
> > changes. Shake vigorously and serve cold..
> > 
> > And maybe the rest of the world can try to make up for the lack of any
> > expected US participation? Hmm?
> 
> Well, unfortunately, this kernel is unusable on my Acer Ferrari One.
> 
> First off, it hangs solid every time several seconds or at last a few
> minutes after boot.  I haven't been able to collect any debug data from
> it yet, but one of the symptoms is black screen with (unmovable) mouse
> cursor (this only happens when X has been started, but the box hangs without
> X too).
> 
> Second, the wireless is apparently unable to associate with the AP
> (that 3.1-rc10 works with correctly on the same box).
> 
> Tomorrow I'll try to identify the offending commits.

Well, it took more time than I had hoped. :-(

Bisection turns up:

commit 2577c6e8f2320f1d2f09be122efef5b9118efee4
Author: Senthil Balasubramanian <senthilb@xxxxxxxxxxxxxxxx>
Date:   Tue Sep 13 22:38:18 2011 +0530

    ath9k_hw: Add support for AR946/8x chipsets.
    
    This patch adds support for AR946/8x chipets.
    
    Signed-off-by: Senthil Balasubramanian <senthilb@xxxxxxxxxxxxxxxx>
    Signed-off-by: John W. Linville <linville@xxxxxxxxxxxxx>

which I think is wrong for at lest two reasons.  Not that I understand
what it actually does to the driver, but first, it does much more than the
changelog says and, second, it is practically impossible to revert
because of the number of commits on top depending on it.  Quite frankly,
it is about to make it to my list of examples of how things should _not_ be
done in the kernel.

The commit immediately preceding it doesn't show any symptoms of failure, so
I'm quite convinced this one really introduced the problem for me.

The chip in the affected box is (according to "lspci -v"):

09:00.0 Network controller: Atheros Communications Inc. AR928X Wireless Network Adapter (PCI-Express) (rev 01)
        Subsystem: Foxconn International, Inc. Device e01f
        Flags: bus master, fast devsel, latency 0, IRQ 19
        Memory at f0000000 (64-bit, non-prefetchable) [size=64K]
        Capabilities: [40] Power Management version 2
        Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit-
        Capabilities: [60] Express Legacy Endpoint, MSI 00
        Capabilities: [90] MSI-X: Enable- Count=1 Masked-
        Capabilities: [100] Advanced Error Reporting
        Capabilities: [140] Virtual Channel
        Capabilities: [160] Device Serial Number 00-00-00-00-00-00-00-00
        Kernel driver in use: ath9k

Thanks,
Rafael
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