On Wed, Nov 4, 2020 at 7:46 AM Tom Rini <trini@xxxxxxxxxxxx> wrote:
>
> Commits 6dcb8ba4 "libfdt: Add helpers for accessing unaligned words"
> introduced changes to support unaligned reads for ARM platforms and
> 11738cf01f15 "libfdt: Don't use memcpy to handle unaligned reads on ARM"
> improved the performance of these helpers.
>
> On further discussion, while there are potential cases where we could be
> used on platforms that do not fixup unaligned reads for us, making this
> choice the default is very expensive in terms of binary size and access
> time. To address this, suffix the existing fdt{32,64}_ld functions with
> _unaligned and introduce new load functions that call
> fdt{32,64}_to_cpu() as was done prior to the above mentioned commits.
>
> Signed-off-by: Tom Rini <trini@xxxxxxxxxxxx>
> ---
> libfdt/libfdt.h | 21 +++++++++++++++------
> 1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/libfdt/libfdt.h b/libfdt/libfdt.h
> index b600c8d6dd41..307ba745c92f 100644
> --- a/libfdt/libfdt.h
> +++ b/libfdt/libfdt.h
> @@ -126,13 +126,22 @@ static inline void *fdt_offset_ptr_w(void *fdt, int offset, int checklen)
> uint32_t fdt_next_tag(const void *fdt, int offset, int *nextoffset);
>
> /*
> - * Alignment helpers:
> - * These helpers access words from a device tree blob. They're
> - * built to work even with unaligned pointers on platforms (ike
> - * ARM) that don't like unaligned loads and stores
> + * Load functions. Assume that we are on a platform where unaligned memory
> + * reads will be handled in a graceful manner and that we do not need to ensure
> + * our reads are aligned. If this is not the case there are _unaligned
> + * versions of these functions that follow and can be used.
> */
> -
> static inline uint32_t fdt32_ld(const fdt32_t *p)
> +{
> + return fdt32_to_cpu(*p);
This changes the public behavior of fdt32_ld() which is one of the
things David was against.
I think we want a _fdt32_ld or fdt32_ld_internal or ?? which is
internal only and doesn't create another ABI.
Rob
