[PATCH v2 2/2] armv8: cpu: Implement allow_unaligned()

[Sam Protsenko]

Usually ARMv8 platforms allow unaligned access for Normal memory. But
some chips might not allow it by default, having SCTLR.A bit set to 1
before U-Boot execution. One such example is Exynos850 SoC. As
allow_unaligned() is not implemented for ARMv8 at the moment, its __weak
implementation is used, which does nothing. That might lead to unaligned
access abort, for example when running EFI selftest. Fix that by
implementing allow_unaligned() for ARMv8.

The issue was found when running EFI selftest on E850-96 board
(Exynos850 based):

    => bootefi selftest $fdtcontroladdr

    ...
    Executing 'HII database protocols'
    "Synchronous Abort" handler, esr 0x96000021, far 0xbaac0991
    ...
    resetting ...

Unaligned abort happens in u16_strnlen(), which is called from
efi_hii_sibt_string_ucs2_block_next():

    u16_strlen(blk->string_text)

where 'blk' type is struct efi_hii_sibt_string_ucs2_block. Because this
struct is packed, doing "->string_text" makes 'blk' address incremented
by 1 byte, which makes it unaligned. Although allow_unaligned() was
called in efi_init_early() before EFI selftest execution, it wasn't
implemented for ARMv8 CPUs, so data abort happened.

Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>
---
Changes in v2:
  - None

 arch/arm/cpu/armv8/cpu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm/cpu/armv8/cpu.c b/arch/arm/cpu/armv8/cpu.c
index d568efa427ab..82ecf02f4b03 100644
--- a/arch/arm/cpu/armv8/cpu.c
+++ b/arch/arm/cpu/armv8/cpu.c
@@ -94,3 +94,8 @@ void armv8_setup_psci(void)
 	secure_ram_addr(psci_arch_init)();
 }
 #endif
+
+void allow_unaligned(void)
+{
+	set_sctlr(get_sctlr() & ~CR_A);
+}
-- 
2.39.5