MIPS: ralink: Fix booting on MT7621

Since commit 3af5a67c86a3 ("MIPS: Fix early CM probing") the MT7621 has
not been able to boot.

This commit caused mips_cm_probe() to be called before
mt7621.c::proc_soc_init().

prom_soc_init() has a comment explaining that mips_cm_probe() "wipes out
the bootloader config" and means that configuration registers are no
longer available. It has some code to re-enable this config.

Before this re-enable code is run, the sysc register cannot be read, so
when SYSC_REG_CHIP_NAME0 is read, a garbage value is returned and
panic() is called.

If we move the config-repair code to the top of prom_soc_init(), the
registers can be read and boot can proceed.

Very occasionally, the first register read after the reconfiguration
returns garbage, so add a call to __sync().

Fixes: 3af5a67c86a3 ("MIPS: Fix early CM probing")
Signed-off-by: NeilBrown <neil@brown.name>
Reviewed-by: Matt Redfearn <matt.redfearn@mips.com>
Cc: John Crispin <john@phrozen.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # 4.5+
Patchwork: https://patchwork.linux-mips.org/patch/18859/
Signed-off-by: James Hogan <jhogan@kernel.org>

arch/mips/ralink/mt7621.c

@@ -170,6 +170,28 @@ void prom_soc_init(struct ralink_soc_info *soc_info)
 	u32 n1;
 	u32 rev;
 
+	/* Early detection of CMP support */
+	mips_cm_probe();
+	mips_cpc_probe();
+
+	if (mips_cps_numiocu(0)) {
+		/*
+		 * mips_cm_probe() wipes out bootloader
+		 * config for CM regions and we have to configure them
+		 * again. This SoC cannot talk to pamlbus devices
+		 * witout proper iocu region set up.
+		 *
+		 * FIXME: it would be better to do this with values
+		 * from DT, but we need this very early because
+		 * without this we cannot talk to pretty much anything
+		 * including serial.
+		 */
+		write_gcr_reg0_base(MT7621_PALMBUS_BASE);
+		write_gcr_reg0_mask(~MT7621_PALMBUS_SIZE |
+				    CM_GCR_REGn_MASK_CMTGT_IOCU0);
+		__sync();
+	}
+
 	n0 = __raw_readl(sysc + SYSC_REG_CHIP_NAME0);
 	n1 = __raw_readl(sysc + SYSC_REG_CHIP_NAME1);
 
@@ -194,26 +216,6 @@ void prom_soc_init(struct ralink_soc_info *soc_info)
 
 	rt2880_pinmux_data = mt7621_pinmux_data;
 
-	/* Early detection of CMP support */
-	mips_cm_probe();
-	mips_cpc_probe();
-
-	if (mips_cps_numiocu(0)) {
-		/*
-		 * mips_cm_probe() wipes out bootloader
-		 * config for CM regions and we have to configure them
-		 * again. This SoC cannot talk to pamlbus devices
-		 * witout proper iocu region set up.
-		 *
-		 * FIXME: it would be better to do this with values
-		 * from DT, but we need this very early because
-		 * without this we cannot talk to pretty much anything
-		 * including serial.
-		 */
-		write_gcr_reg0_base(MT7621_PALMBUS_BASE);
-		write_gcr_reg0_mask(~MT7621_PALMBUS_SIZE |
-				    CM_GCR_REGn_MASK_CMTGT_IOCU0);
-	}
 
 	if (!register_cps_smp_ops())
 		return;