Re: device driver for the SGI system clock, mmtimer

[Vojtech Pavlik]

On Thu, Sep 16, 2004 at 11:35:52AM -0700, Jesse Barnes wrote:
> On Thursday, September 16, 2004 11:14 am, Vojtech Pavlik wrote:
> > On Thu, Sep 16, 2004 at 09:09:12AM -0700, Jesse Barnes wrote:
> > > On Thursday, September 16, 2004 9:03 am, Bjorn Helgaas wrote:
> > > > Christoph Lameter wrote:
> > > > > The timer hardware was designed around the multimedia timer
> > > > > specification by Intel but to my knowledge only SGI has implemented
> > > > > that standard. The driver was written by Jesse Barnes.
> > > >
> > > > As far as I can see, drivers/char/hpet.c talks to the same hardware.
> > > > HP sx1000 machines (and probably others) also implement the HPET.
> > >
> > > No, it's different hardware.
> >
> > mmtimer and hpet are the same hardware actually, just a different
> > specification revision, hpet being the newer one.
> 
> Well, the SHub RTC hardware (which mmtimer accesses) isn't really HPET or 
> mmtimer hardware, but I tried to make the mmtimer *API* useful for HPET style 
> hardware.  The idea was to have several drivers supporting the mmtimer API 
> with different hardware underneath.

Sorry, I got confused by the driver name.

> > HPET registers are MMIO so it's in theory possible, while not really
> > useful if you're using it as your system timer as well.
> 
> I don't think anyone does this.

x86-64 does if SMP is enabled and HPET is present.

-- 
Vojtech Pavlik
SuSE Labs, SuSE CR
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