[U-Boot] [PATCH v2] timer: add High Precision Event Timers (HPET) support

[Ivan Gorinov]

On Sat, Mar 31, 2018 at 06:31:03AM -0600, Andy Shevchenko wrote:
> >> > +               tl = readl(regs + HPET_MAIN_COUNT_L);
> >> > +               th = readl(regs + HPET_MAIN_COUNT_H);
> >>
> >> Ditto.
> >
> > If readq() is defined as two read operations in 32-bit code, main counter
> > rollover (low part overflow, high part increment) can happen between them.
> 
> And how this contradicts ther current code?

It just does not make the code simpler, rollover check is
still required if U-Boot is compiled as 32-bit code.

Can we do something like the following?


#ifdef CONFIG_X86_64

static u64 read_main_counter(void *regs)
{
	return readq(regs + HPET_MAIN_COUNT);
}

#else

/*
 * Read the main counter as two 32-bit registers,
 * repeat if rollover happens.
 */
static u64 read_main_counter(void *regs)
{
	u64 now_tick;
	u32 tl, th, th0;

	th = readl(regs + HPET_MAIN_COUNT_H);
	do {
		th0 = th;
		tl = readl(regs + HPET_MAIN_COUNT_L);
		th = readl(regs + HPET_MAIN_COUNT_H);
		now_tick = th;
		now_tick <<= 32;
		now_tick |= tl;
	} while (th != th0);

	return now_tick;
}

#endif