Re: [PATCH 7/8] x86/mrst: add vrtc driver which serves as a wallclock device

From: Feng Tang
Date: Tue May 18 2010 - 02:14:46 EST

Hi Thomas,

On Mon, 17 May 2010 17:15:55 +0800
Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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,
> tglx
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