On 09/24/2013 10:27 PM, Ralf Baechle wrote:
Commit 006a851b10a395955c153a145ad8241494d43688 adds 74K support in c-r4k.c:
+static inline void alias_74k_erratum(struct cpuinfo_mips *c)
+{
+ /*
+ * Early versions of the 74K do not update the cache tags on a
+ * vtag miss/ptag hit which can occur in the case of KSEG0/KUSEG
+ * aliases. In this case it is better to treat the cache as always
+ * having aliases.
+ */
+ if ((c->processor_id & 0xff) <= PRID_REV_ENCODE_332(2, 4, 0))
+ c->dcache.flags |= MIPS_CACHE_VTAG;
+ if ((c->processor_id & 0xff) == PRID_REV_ENCODE_332(2, 4, 0))
+ write_c0_config6(read_c0_config6() | MIPS_CONF6_SYND);
+ if (((c->processor_id & 0xff00) == PRID_IMP_1074K) &&
+ ((c->processor_id & 0xff) <= PRID_REV_ENCODE_332(1, 1, 0))) {
+ c->dcache.flags |= MIPS_CACHE_VTAG;
+ write_c0_config6(read_c0_config6() | MIPS_CONF6_SYND);
+ }
+}
But MIPS D-caches are never virtually tagged, so there is nothing in
the kernel that ever tests the MIPS_CACHE_VTAG flag in a D-cache
descriptor.
Cargo cult programming at its finest? Or was MIPS_CACHE_ALIASES what
really was meant to be set?
Ralf
There is a problem on early versions of 74K/1074K which can be effectively cured by setting MIPS_CACHE_VTAG.
It enforces the needed cache handling.
I hope it will go away as customers replace RTL for newer versions.
But I prefer the patch version from Maciej W. Rozycki, it is more clear.
- Leonid.
