MIPS: Avoid pipeline stalls on some MIPS32R2 cores.
The architecture specification says that an EHB instruction is
needed to avoid a hazard when writing TLB entries. However, some
cores do not have this hazard, and thus the EHB instruction causes
a costly pipeline stall. Detect these cores and do not use the EHB
instruction.
Signed-off-by: Steven J. Hill <sjhill@mips.com>
diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
index 03eb0ef..22ba108 100644
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -449,8 +449,20 @@
}
if (cpu_has_mips_r2) {
- if (cpu_has_mips_r2_exec_hazard)
+ /*
+ * The architecture spec says an ehb is required here,
+ * but a number of cores do not have the hazard and
+ * using an ehb causes an expensive pipeline stall.
+ */
+ switch (current_cpu_type()) {
+ case CPU_M14KC:
+ case CPU_74K:
+ break;
+
+ default:
uasm_i_ehb(p);
+ break;
+ }
tlbw(p);
return;
}