From: Arnd Bergmann <arnd@arndb•de>
To: linuxppc-dev@ozlabs•org
Cc: Segher Boessenkool <segher@kernel•crashing.org>,
benh@kernel•crashing.org, Nathan Lynch <ntl@pobox•com>,
mcarlson@broadcom•com, Michael Chan <mchan@broadcom•com>,
netdev <netdev@vger•kernel.org>
Subject: Re: Strange tg3 regression with UMP fw. link reporting
Date: Fri, 8 Aug 2008 11:21:30 +0200 [thread overview]
Message-ID: <200808081121.30795.arnd@arndb.de> (raw)
In-Reply-To: <31233EB5-037E-4615-95C9-7C816E510752@kernel.crashing.org>
On Friday 08 August 2008, 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...)
It can potentially be even much longer, because each udelay will wait
for *more* than 10 microseconds, and tr32() is an mmio read that takes
additional time, possibly in the order of microseconds as well.
The correct way to implement a timeout like this would be to use
time_before() in the condition, aside from better not doing a busy-loop
in the first place.
Arnd <><
prev parent reply other threads:[~2008-08-08 9:22 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-08 7:35 Strange tg3 regression with UMP fw. link reporting Benjamin Herrenschmidt
2008-08-08 8:58 ` Segher Boessenkool
2008-08-08 9:18 ` Benjamin Herrenschmidt
2008-08-08 18:43 ` Matt Carlson
2008-08-08 15:20 ` Michael Chan
2008-08-08 22:05 ` Benjamin Herrenschmidt
2008-08-08 20:20 ` Michael Chan
2008-08-08 21:25 ` Nathan Lynch
2008-08-08 9:21 ` Arnd Bergmann [this message]
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