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".
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