Re: [RFC][PATCH] new timeofday core subsystem (v. A3)

[Matt Mackall <mpm@selenic.com>]

On Mon, Mar 14, 2005 at 11:43:21AM -0800, john stultz wrote:
> On Mon, 2005-03-14 at 11:29 -0800, Matt Mackall wrote:
> > On Mon, Mar 14, 2005 at 10:42:45AM -0800, john stultz wrote:
> > > 
> > > > > +static inline cycle_t read_timesource(struct timesource_t* ts)
> > > > > +{
> > > > > +	switch (ts->type) {
> > > > > +	case TIMESOURCE_MMIO_32:
> > > > > +		return (cycle_t)readl(ts->mmio_ptr);
> > > > > +	case TIMESOURCE_MMIO_64:
> > > > > +		return (cycle_t)readq(ts->mmio_ptr);
> > > > > +	case TIMESOURCE_CYCLES:
> > > > > +		return (cycle_t)get_cycles();
> > > > > +	default:/* case: TIMESOURCE_FUNCTION */
> > > > > +		return ts->read_fnct();
> > > > > +	}
> > > > > +}
> > > > 
> > > > Wouldn't it be better to change read_fnct to take a timesource * and
> > > > then change all the other guys to generic_timesource_<foo> helper
> > > > functions? This does away with the switch and makes it trivial to add
> > > > new generic sources. Change mmio_ptr to void *private.
> > > 
> > > Not sure if I totally understand this, but originally I just had a read
> > > function, but to allow this framework to function w/ ia64 fsyscalls (and
> > > likely other arches vsyscalls) we need to pass the raw mmio pointers.
> > > Thus the timesource type and switch idea was taken from the time
> > > interpolator code.
> > 
> > Well for vsyscall, we can leave the mmio_ptr and type. But in-kernel,
> > I think we'd rather always call read_fnct with generic helpers than hit this
> > switch every time.
> 
> Huh. So if I understand you properly, all timesources should have valid
> read_fnct pointers that return the cycle value, however we'll still
> preserve the type and mmio_ptr so fsyscall/vsyscall bits can use them
> externally?

Well where we'd read an MMIO address, we'd simply set read_fnct to
generic_timesource_mmio32 or so. And that function just does the read.
So both that function and read_timesource become one-liners and we
drop the conditional branches in the switch.

-- 
Mathematics is the supreme nostalgia of our time.