[PATCH/RFC] mpc83xx/85xx SysRQ/brk over 8250 console

Kumar Gala galak at kernel.crashing.org
Tue Jan 8 17:11:19 EST 2008

On Jan 7, 2008, at 11:27 PM, Paul Gortmaker wrote:

> It seems that if a break is rec'd on the serial console (as per SysRQ
> or similar) on some 83xx and 85xx processors, then a pulse of IRQs is
> generated which makes the use of SysRQ itself about 99% impossible.  I
> experimented with trying several ACK strategies, but in the end the
> thing which worked best was just to wait for the surge of events to  
> pass
> (a fraction of a second).  The number of events can be on the order of
> 1000 (as reported by /proc/interrupts)
> I really dislike seeing board specific ifdefs within what should be
> board independent code, so I'm hoping that once the problem is known,
> that a more elegant solution will pop into someone's head.  Or at  
> least
> this will hopefully save someone the grief of re-investigating the  
> source
> and start a discussion.
> I've seen this on two different 834x boards and also an 8548 based
> board.  At this point, it is not clear to me if the problem extends
> beyond these CPU/soc to all with UARTs at 4500/4600.
> While less than ideal, the work-around below which simply ignores the
> events does allow a person to use SysRQ on such platforms.
> The definition of the RFE bit (Rx FIFO error) can be found in pretty
> much any of the MPC CPU PDFs (for those with 4500/4600 16550s).
> Paul.

This should really get posted to linux-kernel at vger.kernel.org and  
probably linux-serial at vger.kernel.org lists.

- k

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