firmware: Minor optimization in _scratch_init()

Before entering _scratch_init(), register t3 already holds a copy of the firmware end address, hence there is no need to calculate it again. This reduces 3 instructions in each _scratch_init() loop.

Signed-off-by Bin Meng <[email protected]>

Reviewed-by Xiang W <[email protected]>

Reviewed-by Atish Patra <[email protected]>

---

Changes in v2:
- add a comment block before _scratch_init() documenting all registers used in the loop block

 firmware/fw_base.S | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

firmware/fw_base.S +9 -5

index a5ce946..8e40562 100644
@@ -278,6 +278,14 @@ _bss_zero:
        /* hartid 0 is mandated by ISA */
        li      t1, 0
 _scratch_init:
+       /*
+        * The following registers hold values that are computed before
+        * entering this block, and should remain unchanged.
+        *
+        * t3 -> the firmware end address
+        * s7 -> HART count
+        * s8 -> HART stack size
+        */
        add     tp, t3, zero
        mul     a5, s8, t1
        sub     tp, tp, a5

@@ -287,10 +295,7 @@ _scratch_init:
        /* Initialize scratch space */
        /* Store fw_start and fw_size in scratch space */
        lla     a4, _fw_start
-       lla     a5, _fw_end
-       mul     t0, s7, s8
-       add     a5, a5, t0
-       sub     a5, a5, a4
+       sub     a5, t3, a4
        REG_S   a4, SBI_SCRATCH_FW_START_OFFSET(tp)
        REG_S   a5, SBI_SCRATCH_FW_SIZE_OFFSET(tp)
        /* Store next arg1 in scratch space */
--

2.25.1

--
opensbi mailing list
opensbi at lists.infradead.org
http://lists.infradead.org/mailman/listinfo/opensbi