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

[Ivan Gorinov]

On Tue, Apr 03, 2018 at 06:17:42AM -0600, Andy Shevchenko wrote:
> >> > 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,
> ...b/c you misread what I suggested.
> > rollover check is
> > still required if U-Boot is compiled as 32-bit code.
> > Can we do something like the following?
> Yes, but... why?
> What's wrong with replacing two sequential 32-bit reads with one 64-bit?

Doesn't readX/writeX imply a single I/O operation?
It may be misleading to define it as two.

Assuming MMX or SSE2 to be supported by all x86 processors, 64-bit I/O
registers can be accessed as a single operation even in 32-bit code:

static inline u64 readq(void *addr)
{
	u64 value;

	asm volatile ("movq (%0), %%xmm0" : : "r" (addr));
	asm volatile ("movq %%xmm0, %0" : "=m" (value));

	return value;
}

I can add these definitions to "asm/io.h".