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

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Date:	Mon, 19 Mar 2012 02:34:48 -0400
From:	Jon Masters <jonathan@...masters.org>
To:	Keith Chew <keith.chew@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Hang on "echo b > /proc/sysrq-trigger"

Hi Keith,

I've just been reviewing LKML for the past month…was there ever any followup?
Perhaps it's worth discussing a patch to change the below delay?

Jon.

On Mar 10, 2012, at 6:45 PM, Keith Chew wrote:

> 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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