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Subject: Re: Strange tg3 regression with UMP fw. link reporting
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
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Date: Fri, 08 Aug 2008 19:18:31 +1000
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Cc: linuxppc-dev list <linuxppc-dev@ozlabs.org>, Nathan Lynch <ntl@pobox.com>,
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On Fri, 2008-08-08 at 10:58 +0200, Segher Boessenkool wrote:
> > I don't know yet for sure what happens, but a quick look at the commit
> > seems to show that the driver synchronously spin-waits for up to 2.5ms
> 
> That's what the comment says, but the code says 2.5 _seconds_:
> 
> +       /* Wait for up to 2.5 milliseconds */
> +       for (i = 0; i < 250000; i++) {
> +               if (!(tr32(GRC_RX_CPU_EVENT) & GRC_RX_CPU_DRIVER_EVENT))
> +                       break;
> +               udelay(10);
> +       }
> 
> (not that milliseconds wouldn't be bad already...)

Right, indeed. I think we have a good candidate for the problem :-) I'll
verify that on monday. Now, that leads to two questions:

 - What such a synchronous and potentially horribly slow code is
going in a locked section or a timer interrupts ? Ie, the link
watch should probably move to a workqueue if that is to remain,
or the code turned into a state machine that periodically check for
events, or whatever is more sane than the above.

 - The code should at least display some error and do something sane in
case of timeout such as disabling the new UMP feature instead of
repeatedly looping ...

 - If this is indeed our problem (timing out in the code above), why is
our firmware not emitting the requested event -> maybe the PowerStations
need a tg3 firmware update.

Matt, what's your take on this ?

Cheers,
Ben.