Re: [PATCH resend 5/9] MIPS: sync after cacheflush

Kevin Cernekee
2010-10-18T18:34:40Z

On Mon, Oct 18, 2010 at 6:44 AM, Shinya Kuribayashi <skuribay@pobox.com> wrote:
> I suspect that SYNC insn alone is still not enough, insn't it?  In
> such systems with that 'deep' write buffer and data incoherency is
> visibly observed, there sill may be data write transactions floating
> in the internal bus system.
>
> To make sure that all data (data inside processor's write buffer and
> data floating in the internal bus system), we need the following
> three steps:
>
> 1. Flush data cache
> 2. Uncached, dummy load operation from _DRAM_ (not somewhere else)
> 3. then SYNC instruction

Some systems do require additional steps along those lines, e.g.

# ifdef CONFIG_SGI_IP28
# define fast_iob() \
__asm__ __volatile__( \
".set push\n\t" \
".set noreorder\n\t" \
"lw $0,%0\n\t" \
"sync\n\t" \
"lw $0,%0\n\t" \
".set pop" \
: /* no output */ \
: "m" (*(int *)CKSEG1ADDR(0x1fa00004)) \
: "memory")

Maybe it would be better to use iob() instead of __sync() directly, so
that it is easy to add extra steps for the CPUs that need them. DEC
and Loongson have custom __wbflush() implementations, and something
similar could be added for your processor to implement the uncached
dummy load.

What do you think?