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

Thomas Gleixner
2010-05-18T07:38:59Z

On Tue, 18 May 2010, Feng Tang wrote:
> Hi Thomas,
>
>
> On Mon, 17 May 2010 17:15:55 +0800
> Thomas Gleixner <tglx@linutronix.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()

John was away yesterday, so we have to wait for his answer, but I don't
expect a nono from him.

> > > > > + 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.

Grr. Yes, missed that the code is called under rtc_lock already. So
you can drop the locking in your code completely.

Thanks,

tglx