linux-kernel - Re: Hang on "echo b > /proc/sysrq-trigger"

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Message-ID: <CAKaWdxaaKMiwnhP7R786mqHTPs+o=izerZDbUgPBaxyU+XL-2g@mail.gmail.com>
Date:	Sun, 11 Mar 2012 12:45:48 +1300
From:	Keith Chew <keith.chew@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Hang on "echo b > /proc/sysrq-trigger"

Hi Eric

Keep a quick update...

>> I would check with your BIOS folks and perhaps play with the kernel
>> option.  The most reliable way to peform a reset is to trigger a board
>> reset by writing to 0xcf9 or a similar register.  I expect your BIOS
>> does that and you can probably get the kernel to do that.  I would
>> definitely test to see if you can write to the mostly standard
>> 0xcf9 register directly from the kernel and trigger a reset directly.
>>

Thank you very much for this. We have tried with reboot=p, which is
writing to the 0xCF9 register directly, and the test has been running
good for the past 9 days. Will keep monitoring it.

Also, I have also added a delay in the KBD reboot, which appears to
have made the reboot reliable (running good for past 8 days, before it
would hang after 2 days):
-----------------------
kb_wait();
udelay(150); <------ Increased from 50
outb(0xfe, 0x64); /* pulse reset low */
udelay(50);
-----------------------

Looks like the code may be issuing the reboot a bit too early after
returning from kb_wait().

Regards
Keith
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