[U-Boot] [PATCH v2] fdt: Fix alignment issue when reading 64-bits properties from fdt

[Simon Glass]

On Tue, 22 Oct 2019 at 02:05, Jean-Jacques Hiblot <jjhiblot at ti.com> wrote:
>
> The FDT specification [0] gives a requirement of aligning properties on
> 32-bits. Make sure that the compiler is aware of this constraint when
> accessing 64-bits properties.
>
> [0]: https://github.com/devicetree-org/devicetree-specification/blob/master/source/flattened-format.rst
>
> Signed-off-by: Jean-Jacques Hiblot <jjhiblot at ti.com>
> ---
>
> Here is a portion of the disassembly of ofnode_read_u64(). It show the effect
> of the patch on ARM64.
>
> with the classic fdt64_t type. GCC emits LDR (load register)
>   34:   54000109        b.ls    54 <ofnode_read_u64+0x54>  // b.plast
>   38:   f9400000        ldr     x0, [x0]
>   3c:   dac00c00        rev     x0, x0
>
> with the unaligned_fdt64_t type. GCC emits LDP (Load Pair of registers)
>   34:   54000129        b.ls    58 <ofnode_read_u64+0x58>  // b.plast
>   38:   29400001        ldp     w1, w0, [x0]
>   3c:   aa008020        orr     x0, x1, x0, lsl #32
>   40:   dac00c00        rev     x0, x0
>
>
>  common/fdt_support.c       | 2 +-
>  drivers/core/ofnode.c      | 2 +-
>  include/linux/libfdt_env.h | 1 +
>  lib/fdtdec.c               | 2 +-
>  4 files changed, 4 insertions(+), 3 deletions(-)

Reviewed-by: Simon Glass <sjg at chromium.org>

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