m68k/mac: Make SCC reset work more reliably

For SCC initialization we cannot assume that the control register is in
the correct state to accept a register pointer. So first read from the
control register in order to "sync" up.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/m68k/kernel/head.S b/arch/m68k/kernel/head.S
index 7d7913f5dce3..4c99bab7e664 100644
--- a/arch/m68k/kernel/head.S
+++ b/arch/m68k/kernel/head.S
@@ -2915,7 +2915,9 @@ func_start	serial_init,%d0/%d1/%a0/%a1
 
 #if defined(MAC_USE_SCC_A) || defined(MAC_USE_SCC_B)
         movel   %pc@(L(mac_sccbase)),%a0
-        /* Reset SCC device */
+        /* Reset SCC register pointer */
+        moveb   %a0@(mac_scc_cha_a_ctrl_offset),%d0
+        /* Reset SCC device: write register pointer then register value */
         moveb   #9,%a0@(mac_scc_cha_a_ctrl_offset)
         moveb   #0xc0,%a0@(mac_scc_cha_a_ctrl_offset)
         /* Wait for 5 PCLK cycles, which is about 68 CPU cycles */