[PATCH v2] MIPS: ralink: fix booting on mt7621

[NeilBrown]

Further testing showed that the original version of this
patch wasn't 100% reliable.  Very occasionally the read
of SYSC_REG_CHIP_NAME0 returns garbage.  Repeating the
read seems to be reliable, but it hasn't happened enough
for me to be completely confident.
So this version repeats that first read.

Thanks,
NeilBrown


----------------8<--------------------
Since commit 3af5a67c86a3 ("MIPS: Fix early CM probing") the MT7621
has not been able to boot.

This patched 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 repeat that read to be on the safe side.

Fixes: 3af5a67c86a3 ("MIPS: Fix early CM probing")
Signed-off-by: NeilBrown <neil@xxxxxxxxxx>
---
 arch/mips/ralink/mt7621.c | 43 +++++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/arch/mips/ralink/mt7621.c b/arch/mips/ralink/mt7621.c
index 1b274742077d..c37716407fbe 100644
--- a/arch/mips/ralink/mt7621.c
+++ b/arch/mips/ralink/mt7621.c
@@ -170,6 +170,29 @@ 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);
+	}
+
+	n0 = __raw_readl(sysc + SYSC_REG_CHIP_NAME0);
+	/* Sometimes first read returns garbage, so try again to be safe */
 	n0 = __raw_readl(sysc + SYSC_REG_CHIP_NAME0);
 	n1 = __raw_readl(sysc + SYSC_REG_CHIP_NAME1);
 
@@ -194,26 +217,6 @@ 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;
-- 
2.14.0.rc0.dirty

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