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


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