linux-kernel - Re: [PATCH] ARM: Add support for LPAE style CONTEXTIDR

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Message-ID: <20130626171138.GF10333@mudshark.cambridge.arm.com>
Date:	Wed, 26 Jun 2013 18:11:38 +0100
From:	Will Deacon <will.deacon@....com>
To:	Christopher Covington <cov@...eaurora.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Nicolas Pitre <nico@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: Add support for LPAE style CONTEXTIDR

On Mon, Jun 24, 2013 at 04:15:06PM +0100, Christopher Covington wrote:
> On 06/24/2013 10:53 AM, Will Deacon wrote:
> > On Mon, Jun 24, 2013 at 03:39:09PM +0100, Christopher Covington wrote:
> >> Hi Will,
> >>
> >> On 06/24/2013 10:04 AM, Will Deacon wrote:
> >> [...]
> >>
> >>> What's the advantage of this approach, other than you get an extra byte's
> >>> worth of PID?
> >>
> >> In my view, the real advantage is that the the PID is located where people
> >> reading ARM Architecture Reference Manual are told they can find it.
> > 
> > Perhaps, but I'd usually expect a debugger or trace tools to do something
> > with the PID, and they likely expect it to be shifted, so you can't really
> > win.
> 
> But reading and implementing the architecture *is* winning! LOL. I'll file a
> ticket with the architecture folks and see what they think.

...aaand that came full circle :)

I think the conclusion is that Linux PID != CONTEXTIDR.PROCID, so there's no
architectural issue here. I'm just trying to keep it easy for the tools.

Will
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