linux-kernel - Re: [PATCH] arm64: kernel: compiling issue, need 'EXPORT_SYMBOL_GPL(read_current

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Message-ID: <20130520095606.GH31359@mudshark.cambridge.arm.com>
Date:	Mon, 20 May 2013 10:56:06 +0100
From:	Will Deacon <will.deacon@....com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Chen Gang <gang.chen@...anux.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Tony Lindgren <tony@...mide.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: kernel: compiling issue, need
 'EXPORT_SYMBOL_GPL(read_current_timer)'

On Mon, May 20, 2013 at 08:15:04AM +0100, Marc Zyngier wrote:
> On Mon, 20 May 2013 14:48:05 +0800, Chen Gang <gang.chen@...anux.com>
> wrote:
> > Need 'EXPORT_SYMBOL_GPL(read_current_timer)' if build with allmodconfig.
> > 
> > The related error:
> >   ERROR: "read_current_timer" [lib/rbtree_test.ko] undefined!
> >   ERROR: "read_current_timer" [lib/interval_tree_test.ko] undefined!
> >   ERROR: "read_current_timer" [fs/ext4/ext4.ko] undefined!
> >   ERROR: "read_current_timer" [crypto/tcrypt.ko] undefined!
> > 
> > 
> > Signed-off-by: Chen Gang <gang.chen@...anux.com>
> > ---
> >  arch/arm64/kernel/time.c |    1 +
> >  1 files changed, 1 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c
> > index a551f88..7fcba80 100644
> > --- a/arch/arm64/kernel/time.c
> > +++ b/arch/arm64/kernel/time.c
> > @@ -73,6 +73,7 @@ int read_current_timer(unsigned long *timer_value)
> >  	*timer_value = arch_timer_read_counter();
> >  	return 0;
> >  }
> > +EXPORT_SYMBOL_GPL(read_current_timer);
> >  
> >  void __init time_init(void)
> >  {
> 
> While this solves the problem, I'm not sure this is the best fix. The real
> issue is with get_cycles, which is a macro around read_current_timer.
> 
> AArch32 exports it because of the number of timer implementations. On
> arm64, we should be able to just return CNTVCT_EL0.
> 
> Catalin, Will, what do you think?

Should be ok once the arch timer driver has moved exclusively to virtual
time. I'm also not sure we even need to implement read_current_timer() --
it's only used for delay-loop calibration, which we don't need for the
arch timer.

Will
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