Re: [RFC] Hardware Breakpoint interfaces implementation for PPC64

From: "K.Prasad" <prasad@linux.vnet.ibm.com>
To: Josh Boyer <jwboyer@linux.vnet.ibm.com>,
	linuxppc-dev@ozlabs.org,
	Benjamin Herrenschmidt <benh@au1.ibm.com>,
	paulus@samba.org
Subject: Re: [RFC] Hardware Breakpoint interfaces implementation for PPC64
Date: Fri, 15 May 2009 00:22:34 +0530	[thread overview]
Message-ID: <20090514185234.GB30963@in.ibm.com> (raw)
In-Reply-To: <20090513025717.GN24338@yookeroo.seuss>

On Wed, May 13, 2009 at 12:57:17PM +1000, David Gibson wrote:
> On Wed, May 13, 2009 at 01:55:45AM +0530, K.Prasad wrote:
> > On Tue, May 12, 2009 at 07:51:49AM -0400, Josh Boyer wrote:
> > > On Tue, May 12, 2009 at 01:33:55AM +0530, K.Prasad wrote:
> [snip]
> 
> It seems to me that a kind of minimal requirement for a sensible
> generic debug interface is that if no processes actually ask to use
> the debug regs, then we should never touch them in the hardware.  This
> means that debugging hacks in the kernel can just use the debug regs
> directly and don't have to go through the interface to avoid having
> their stuff clobbered on context switch.
> 

All that we do additionally for kernel users (when no process is
currently using the debug regs) is to account for the usage just so that
any new requests (kernel or user-space) are denied.

> -- 
> David Gibson			| I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
> 				| _way_ _around_!
> http://www.ozlabs.org/~dgibson

Thanks,
K.Prasad