linux-kernel - Re: [PATCH v1 1/6] arm: fiq: Replace default FIQ handler

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Date:	Fri, 5 Sep 2014 14:04:03 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Daniel Thompson <daniel.thompson@...aro.org>
cc:	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	patches@...aro.org, linaro-kernel@...ts.linaro.org,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v1 1/6] arm: fiq: Replace default FIQ handler

On Fri, 5 Sep 2014, Daniel Thompson wrote:

> On 04/09/14 19:57, Nicolas Pitre wrote:
> > On Thu, 4 Sep 2014, Daniel Thompson wrote:
> > 
> >> +@ svc_exit_via_fiq - similar to svc_exit but switches to FIQ mode before exit
> >> +@
> >> +@ This macro acts in a similar manner to svc_exit but switches to FIQ
> >> +@ mode to restore the final part of the register state.
> >> +@
> >> +@ We cannot use the normal svc_exit procedure because that would
> >> +@ clobber spsr_svc (FIQ could be delivered during the first few instructions
> >> +@ of vector_swi meaning its contents have not been saved anywhere).
> >> +@
> > 
> > Wouldn't it be better for this macro to live in entry-header.S alongside 
> > the others?
> 
> I'm not sure either way.
> 
> svc_exit_from_fiq isn't needed by entry-common.S and cannot be used by
> entry-v7m.S because v7m has no FIQ. For that reason I decided to place
> it alongside svc_entry in entry-armv.S rather than alongside svc_exit in
> entry-header.S .

Here's a list of macros from entry-headers.S that I don't see being used 
in entry-v7m.S: zero_fp, alignment_trap, store_user_sp_lr, 
load_user_sp_lr, svc_exit, ct_user_exit, ct_user_enter.

Yet, entry-header.S contains macros such as v7m_exception_entry and 
v7m_exception_slow_exit which are unlikely to ever be used in 
entry-armv.S.

> I am happy to move it if you have a strong preference here. Please let
> me know.

I don't have a strong preference, but a preference nevertheless.

It just looks odd that a file is already dedicated to gather all those 
macros for similar purposes and this one is not there.  That makes 
future code review/maintenance a bit annoying if similar things are not 
kept in one place.


Nicolas
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