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firmware: Simplify FDT header endianness conversion

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Reduce the code size by using single-byte loads instead of bit
manipulation. This method also does the right thing on (hypothetical)
big-endian systems.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
This commit is contained in:
Samuel Holland
2024-08-29 13:13:52 -07:00
committed by Anup Patel
parent 7179e36ce7
commit 7c40909159
1 changed files with 5 additions and 21 deletions
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26
firmware/fw_base.S
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@@ -242,30 +242,14 @@ _scratch_init:
beq t1, a1, _fdt_reloc_done
/* t0 = source FDT start address */
add t0, a1, zero
/* t2 = source FDT size in big-endian */
#if __riscv_xlen > 32
lwu t2, 4(t0)
#else
lw t2, 4(t0)
#endif
/* t3 = bit[15:8] of FDT size */
add t3, t2, zero
srli t3, t3, 16
and t3, t3, a4
/* t2 = source FDT size (convert from big-endian) */
lbu t2, 7(t0)
lbu t3, 6(t0)
lbu t4, 5(t0)
lbu t5, 4(t0)
slli t3, t3, 8
/* t4 = bit[23:16] of FDT size */
add t4, t2, zero
srli t4, t4, 8
and t4, t4, a4
slli t4, t4, 16
/* t5 = bit[31:24] of FDT size */
add t5, t2, zero
and t5, t5, a4
slli t5, t5, 24
/* t2 = bit[7:0] of FDT size */
srli t2, t2, 24
and t2, t2, a4
/* t2 = FDT size in little-endian */
or t2, t2, t3
or t2, t2, t4
or t2, t2, t5