ARM: 7691/1: mm: kill unused TLB_CAN_READ_FROM_L1_CACHE and use ALT_SMP instead

Many ARMv7 cores have hardware page table walkers that can read the L1
cache. This is discoverable from the ID_MMFR3 register, although this
can be expensive to access from the low-level set_pte functions and is a
pain to cache, particularly with multi-cluster systems.

A useful observation is that the multi-processing extensions for ARMv7
require coherent table walks, meaning that we can make use of ALT_SMP
patching in proc-v7-* to patch away the cache flush safely for these
cores.

Reported-by: Albin Tonnerre <Albin.Tonnerre@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 3a3c015f8d5c..37716b0508e1 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -75,14 +75,14 @@ ENTRY(cpu_v7_do_idle)
 ENDPROC(cpu_v7_do_idle)
 
 ENTRY(cpu_v7_dcache_clean_area)
-#ifndef TLB_CAN_READ_FROM_L1_CACHE
+        ALT_SMP(mov     pc, lr)                 @ MP extensions imply L1 PTW
+        ALT_UP(W(nop))
         dcache_line_size r2, r3
 1:      mcr     p15, 0, r0, c7, c10, 1          @ clean D entry
         add     r0, r0, r2
         subs    r1, r1, r2
         bhi     1b
         dsb
-#endif
         mov     pc, lr
 ENDPROC(cpu_v7_dcache_clean_area)