mips: mt7620: fallback to SDRAM when syscfg0 does not have a valid value for the memory type

Mediatek MT7620 SoC has syscfg0 bits where it sets the type of memory being used.
However, sometimes those bits are not set properly (reading "11"). In this case, the SoC assumes SDRAM.
The patch below reflects that.
Signed-off-by: Sashka Nochkin <linux-mips@durdom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13135/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/mach-ralink/mt7620.h

@@ -72,6 +72,7 @@
 #define SYSCFG0_DRAM_TYPE_SDRAM		0
 #define SYSCFG0_DRAM_TYPE_DDR1		1
 #define SYSCFG0_DRAM_TYPE_DDR2		2
+#define SYSCFG0_DRAM_TYPE_UNKNOWN	3
 
 #define SYSCFG0_DRAM_TYPE_DDR2_MT7628	0
 #define SYSCFG0_DRAM_TYPE_DDR1_MT7628	1

arch/mips/ralink/mt7620.c

@@ -581,11 +581,14 @@ void prom_soc_init(struct ralink_soc_info *soc_info)
 		(rev & CHIP_REV_ECO_MASK));
 
 	cfg0 = __raw_readl(sysc + SYSC_REG_SYSTEM_CONFIG0);
-	if (is_mt76x8())
+	if (is_mt76x8()) {
 		dram_type = cfg0 & DRAM_TYPE_MT7628_MASK;
-	else
+	} else {
 		dram_type = (cfg0 >> SYSCFG0_DRAM_TYPE_SHIFT) &
 			    SYSCFG0_DRAM_TYPE_MASK;
+		if (dram_type == SYSCFG0_DRAM_TYPE_UNKNOWN)
+			dram_type = SYSCFG0_DRAM_TYPE_SDRAM;
+	}
 
 	soc_info->mem_base = MT7620_DRAM_BASE;
 	if (is_mt76x8())