[PATCH] Revert "riscv: Add a Zalrsc-only alternative for synchronization in start.S"

[Yao Zi]

This reverts commit a681cfecb4346107212f377e2075f6eb1bdc6a2b.

It has been reported that the commit causes boot regression for SPL on
StarFive VisionFive 2 or compatible boards. Inspecting the code, I did
spot one logic error for deciding whether Zaamo or Zalrsc is used, and
it's still unclear what exactly causes the regression, let's revert it
for now.

Reported-by: E Shattow <e at freeshell.de>
Link: https://lore.kernel.org/u-boot/1871663e-b918-4351-9e9e-97f9a4c73733@freeshell.de/
Signed-off-by: Yao Zi <ziyao at disroot.org>
---

The original series causing the problem[1] contains 3 patches, and I
think it should be enough to revert the change of start.S only, since
the others touch no code, and should be relatively safe. I'll fix the
reverted change up and get it work on VisionFive 2 when I got my new
board. Sorry for the inconvenience.

[1]: https://lore.kernel.org/u-boot/20250902081932.21103-1-ziyao@disroot.org/

 arch/riscv/cpu/start.S | 26 +-------------------------
 1 file changed, 1 insertion(+), 25 deletions(-)

diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
index 6324ff585d4..7bafdfd390a 100644
--- a/arch/riscv/cpu/start.S
+++ b/arch/riscv/cpu/start.S
@@ -151,15 +151,8 @@ call_harts_early_init:
 	 */
 	la	t0, hart_lottery
 	li	t1, 1
-#if CONFIG_IS_ENABLED(RISCV_ISA_ZAAMO)
 	amoswap.w s2, t1, 0(t0)
 	bnez	s2, wait_for_gd_init
-#else
-	lr.w	s2, (t0)
-	bnez	s2, wait_for_gd_init
-	sc.w	s2, t1, (t0)
-	bnez	s2, wait_for_gd_init
-#endif
 #else
 	/*
 	 * FIXME: gp is set before it is initialized. If an XIP U-Boot ever
@@ -184,12 +177,7 @@ call_harts_early_init:
 #if !CONFIG_IS_ENABLED(XIP)
 #ifdef CONFIG_AVAILABLE_HARTS
 	la	t0, available_harts_lock
-#if CONFIG_IS_ENABLED(RISCV_ISA_ZAAMO)
 	amoswap.w.rl zero, zero, 0(t0)
-#else
-	fence	rw, w
-	sw	zero, 0(t0)
-#endif
 #endif
 
 wait_for_gd_init:
@@ -202,14 +190,7 @@ wait_for_gd_init:
 #ifdef CONFIG_AVAILABLE_HARTS
 	la	t0, available_harts_lock
 	li	t1, 1
-1:
-#if CONFIG_IS_ENABLED(RISCV_ISA_ZAAMO)
-	amoswap.w.aq t1, t1, 0(t0)
-#else
-	lr.w.aq	t1, 0(t0)
-	bnez	t1, 1b
-	sc.w.rl t1, t1, 0(t0)
-#endif
+1:	amoswap.w.aq t1, t1, 0(t0)
 	bnez	t1, 1b
 
 	/* register available harts in the available_harts mask */
@@ -219,12 +200,7 @@ wait_for_gd_init:
 	or	t2, t2, t1
 	SREG	t2, GD_AVAILABLE_HARTS(gp)
 
-#if CONFIG_IS_ENABLED(RISCV_ISA_ZAAMO)
 	amoswap.w.rl zero, zero, 0(t0)
-#else
-	fence	rw, w
-	sw	zero, 0(t0)
-#endif
 #endif
 
 	/*
-- 
2.50.1