MIPS: BCM47XX: Fix reboot problem on BCM4705/BCM4785

This adds some code based on code from the Broadcom GPL tar to fix the
reboot problems on BCM4705/BCM4785. I tried rebooting my device for ~10
times and have never seen a problem. This reverts the changes in the
previous commit and adds the real fix as suggested by Rafał.

Setting bit 22 in Reg 22, sel 4 puts the BIU (Bus Interface Unit) into
async mode.

The previous commit was 316cad5c [MIPS:
BCM47XX: make reboot more relaiable]
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: jogo@openwrt.org
Cc: zajec5@gmail.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7545/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/bcm47xx/setup.c

@@ -59,12 +59,21 @@ static void bcm47xx_machine_restart(char *command)
 	switch (bcm47xx_bus_type) {
 #ifdef CONFIG_BCM47XX_SSB
 	case BCM47XX_BUS_TYPE_SSB:
-		ssb_watchdog_timer_set(&bcm47xx_bus.ssb, 3);
+		if (bcm47xx_bus.ssb.chip_id == 0x4785)
+			write_c0_diag4(1 << 22);
+		ssb_watchdog_timer_set(&bcm47xx_bus.ssb, 1);
+		if (bcm47xx_bus.ssb.chip_id == 0x4785) {
+			__asm__ __volatile__(
+				".set\tmips3\n\t"
+				"sync\n\t"
+				"wait\n\t"
+				".set\tmips0");
+		}
 		break;
 #endif
 #ifdef CONFIG_BCM47XX_BCMA
 	case BCM47XX_BUS_TYPE_BCMA:
-		bcma_chipco_watchdog_timer_set(&bcm47xx_bus.bcma.bus.drv_cc, 3);
+		bcma_chipco_watchdog_timer_set(&bcm47xx_bus.bcma.bus.drv_cc, 1);
 		break;
 #endif
 	}