linux-kernel - Re: [PATCH 3.17-rc4 v5 2/6] arm: fiq: Replace default FIQ handler

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Date:	Fri, 12 Sep 2014 18:19:08 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3.17-rc4 v5 2/6] arm: fiq: Replace default FIQ handler

On Fri, Sep 12, 2014 at 06:14:04PM +0100, Russell King - ARM Linux wrote:
> On Thu, Sep 11, 2014 at 12:31:14PM +0100, Daniel Thompson wrote:
> > This patch introduces a new default FIQ handler that is structured in a
> > similar way to the existing ARM exception handler and result in the FIQ
> > being handled by C code running on the SVC stack (despite this code run
> > in the FIQ handler is subject to severe limitations with respect to
> > locking making normal interaction with the kernel impossible).
> > 
> > This default handler allows concepts that on x86 would be handled using
> > NMIs to be realized on ARM.
> 
> Okay, lastly... I sent you my version of this change, which contained
> the changes I've detailed in the previous three emails, which are absent
> from your version.
> 
> However, you've taken on board the "trace" thing to svc_entry, and
> renamed it to "call_trace".
> 
> Now if I add this to usr_entry, "call_trace" doesn't make any sense,
> nor does the .if/.endif placement because it's not just trace_hardirqs_off
> which needs to be disabled there, but also ct_user_exit as well.
> 
> I'm beginning to wonder why I tried to be nice here... it would've been
> a lot faster for me to take your patch, make my own changes and commit
> that instead.
> 
> Frustrated.

And another thing you're missing are the updates to arch/arm/kernel/fiq.c
to ensure that the FIQ registers are preserved when we restore this new
default FIQ handler.

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