linux-kernel - Re: [PATCH 7/8] x86/mrst: add vrtc driver which serves as a wall clock device

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Date:	Tue, 18 May 2010 14:27:19 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	"Du, Alek" <alek.du@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>
Subject: Re: [PATCH 7/8] x86/mrst: add vrtc driver which serves as a wall
 clock device

Hi Thomas,


On Mon, 17 May 2010 17:15:55 +0800
Thomas Gleixner <tglx@...utronix.de> wrote:


> > 
> > Actually when to init the vrtc register is a big problem for me,
> > vrtc need be inited before timekeeping_init(), and I thought better
> > to put it somewhere in setup_arch(), as it is architecture
> > specific, and ioremap is not working at that time. Also that's the
> > reason I created a new wallclock_init func for x86_platforms, I
> > could not find a better way to do the vrtc init.
> 
> There is no particular reason why we need to read it in
> timekeeping_init(). Nothing in the kernel needs the correct wall time
> at that point. So we can safely move the setting of xtime to rtc wall
> clock time to a separate timekeeping_late_init() function.
> 
> John ???
>  
Yeah, good suggestion, if xtime init is moved to a later time in kernel
init flow, then vrtc's init function can be set a arch_initcall()


> > > > +	lock_cmos_prefix(reg);
> > > 
> > >   This lock_cmos magic should just die. I have no idea why
> > > something wants or wanted to access the RTC from an NMI.
> > 
> > I will try to reuse the rtc_lock defined in rtc.c whose get/set_time
> > service won't be called with vrtc's at the same time.
> 
> Please don't create artifical dependencies. Use a separate vrtc_lock
> to serialize the access to vrtc.
I just checked the code, when wall clock's get/set_time service is called,
it is always protected by rtc_lock(code in arch/x86/kernel/rtc.c), then
no need to add the lock for each individual register read/write operation.

I will submit a v2 vrtc patch.

Thanks,
Feng


> 
> Thanks,
> 
> 	tglx
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