[U-Boot] [PATCH v2 1/2] powerpc: mpc83xx: Minimize r1 modification

[Mario Six]

The r1 register is modified several times during the cache-ram setup of
the MPC83xx SoCs.

Since this SP modification confuses debuggers, we use a general purpose
register to compute the new stack pointer value, and only set the SP
once after all computations are done.

Signed-off-by: Mario Six <mario.six at gdsys.cc>
---

Changes in v2:

Patch added (following a suggestion by Joakim Tjernlund)

---
 arch/powerpc/cpu/mpc83xx/start.S | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/cpu/mpc83xx/start.S b/arch/powerpc/cpu/mpc83xx/start.S
index 0001687703..c366f615e7 100644
--- a/arch/powerpc/cpu/mpc83xx/start.S
+++ b/arch/powerpc/cpu/mpc83xx/start.S
@@ -258,14 +258,17 @@ in_flash:
 #endif

 	/* set up the stack pointer in our newly created
-	 * cache-ram (r1) */
-	lis	r1, (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET)@h
-	ori	r1, r1, (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET)@l
+	 * cache-ram; use r3 to keep the new SP for now to
+	 * avoid overiding the SP it uselessly */
+	lis	r3, (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET)@h
+	ori	r3, r3, (CONFIG_SYS_INIT_RAM_ADDR + CONFIG_SYS_GBL_DATA_OFFSET)@l

 	li	r0, 0		/* Make room for stack frame header and	*/
-	stwu	r0, -4(r1)	/* clear final stack frame so that	*/
-	stwu	r0, -4(r1)	/* stack backtraces terminate cleanly	*/
+	stwu	r0, -4(r3)	/* clear final stack frame so that	*/
+	stwu	r0, -4(r3)	/* stack backtraces terminate cleanly	*/

+	/* Finally, actually set SP */
+	mr	r1, r3

 	/* let the C-code set up the rest	                    */
 	/*				                            */
--
2.11.0