arm64: remove unnecessary cache flush at boot

Currently we flush the entire dcache at boot within __cpu_setup, but
this is unnecessary as the booting protocol demands that the dcache is
invalid and off upon entering the kernel. The presence of the cache
flush only serves to hide bugs in bootloaders, and is not safe in the
presence of SMP.

In an SMP boot scenario the CPUs enter coherency outside of the kernel,
and the primary CPU enables its caches before bringing up secondary
CPUs. Therefore if any secondary CPU has an entry in its cache (in
violation of the boot protocol), the primary CPU might snoop it even if
the secondary CPU's cache is disabled. The boot-time cache flush only
serves to hide a firmware bug, and slows down a cpu boot unnecessarily.

This patch removes the unnecessary boot-time cache flush.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
[catalin.marinas@arm.com: make __flush_dcache_all local only]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit bff705950e2cdcf35641dee35eb14bad9ed49e8f)
Signed-off-by: Mark Brown <broonie@linaro.org>

diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
index 1ea9f26d1b703585537d82cf30aa44ddbe879917..6a3c378f3292f3a4caabdd425969f0f22c80fa5b 100644 (file)
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -30,7 +30,7 @@
  *
  *     Corrupted registers: x0-x7, x9-x11
  */
-ENTRY(__flush_dcache_all)
+__flush_dcache_all:
        dsb     sy                              // ensure ordering with previous memory accesses
        mrs     x0, clidr_el1                   // read clidr
        and     x3, x0, #0x7000000              // extract loc from clidr

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 9ef7633a8eb964d5315702703eae98febe1ec5f5..8e0158f198d7d0d5857592ff5232fbb692546792 100644 (file)
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -104,12 +104,6 @@ ENDPROC(cpu_do_switch_mm)
  *     value of the SCTLR_EL1 register.
  */
 ENTRY(__cpu_setup)
-       /*
-        * Preserve the link register across the function call.
-        */
-       mov     x28, lr
-       bl      __flush_dcache_all
-       mov     lr, x28
        ic      iallu                           // I+BTB cache invalidate
        tlbi    vmalle1is                       // invalidate I + D TLBs
        dsb     sy