4 Apr
2018
4 Apr
'18
6:40 a.m.
On Wed, Apr 04, 2018 at 12:15:24PM +0800, Bin Meng wrote:
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:
Adding such requirement (MMX or SSE2) to U-Boot is not good. Why do we require MMX or SSE2 for readq? Can we use general purpose registers?
In 32-bit code, we can't make a 64-bit memory read operation using only general purpose registers.
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".