MIPS: start.S: set sp register directly
The current code uses two instructions to load
the stack pointer into the 'sp' register.
This results in the following assembly code:
468: 3c088040 lui t0,0x8040
46c: 251d0000 addiu sp,t0,0
The first instuction loads the stack pointer into
the 't0' register then the value of the 'sp' register
is computed by adding zero to the value of the 't0'
register. The same issue present on the 64-bit version
as well:
56c: 3c0c8040 lui t0,0x8040
570: 659d0000 daddiu sp,t0,0
Change the code to load the stack pointer directly
into the 'sp' register. The generated code is functionally
equivalent to the previous version but it is simpler.
32-bit:
468: 3c1d8040 lui sp,0x8040
64-bit:
56c: 3c1d8040 lui sp,0x8040
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>
diff --git a/arch/mips/cpu/mips64/start.S b/arch/mips/cpu/mips64/start.S
index aed82e1..d3c5cea 100644
--- a/arch/mips/cpu/mips64/start.S
+++ b/arch/mips/cpu/mips64/start.S
@@ -137,8 +137,7 @@
#endif
/* Set up temporary stack */
- dli t0, CONFIG_SYS_SDRAM_BASE + CONFIG_SYS_INIT_SP_OFFSET
- dla sp, 0(t0)
+ dli sp, CONFIG_SYS_SDRAM_BASE + CONFIG_SYS_INIT_SP_OFFSET
dla t9, board_init_f
jr t9