diff --git a/arch/mips/include/asm/mach-ralink/rt305x.h b/arch/mips/include/asm/mach-ralink/rt305x.h
index 80cda8af7ac9..069bf37a6010 100644
--- a/arch/mips/include/asm/mach-ralink/rt305x.h
+++ b/arch/mips/include/asm/mach-ralink/rt305x.h
@@ -157,4 +157,10 @@ static inline int soc_is_rt5350(void)
 #define RT3352_RSTCTRL_UDEV		BIT(25)
 #define RT3352_SYSCFG1_USB0_HOST_MODE	BIT(10)
 
+#define RT305X_SDRAM_BASE		0x00000000
+#define RT305X_MEM_SIZE_MIN		2
+#define RT305X_MEM_SIZE_MAX		64
+#define RT3352_MEM_SIZE_MIN		2
+#define RT3352_MEM_SIZE_MAX		256
+
 #endif
diff --git a/arch/mips/ralink/rt305x.c b/arch/mips/ralink/rt305x.c
index 6aa3cb1a8fc5..ca7ee3a33790 100644
--- a/arch/mips/ralink/rt305x.c
+++ b/arch/mips/ralink/rt305x.c
@@ -122,6 +122,40 @@ struct ralink_pinmux rt_gpio_pinmux = {
 	.wdt_reset = rt305x_wdt_reset,
 };
 
+static unsigned long rt5350_get_mem_size(void)
+{
+	void __iomem *sysc = (void __iomem *) KSEG1ADDR(RT305X_SYSC_BASE);
+	unsigned long ret;
+	u32 t;
+
+	t = __raw_readl(sysc + SYSC_REG_SYSTEM_CONFIG);
+	t = (t >> RT5350_SYSCFG0_DRAM_SIZE_SHIFT) &
+		RT5350_SYSCFG0_DRAM_SIZE_MASK;
+
+	switch (t) {
+	case RT5350_SYSCFG0_DRAM_SIZE_2M:
+		ret = 2;
+		break;
+	case RT5350_SYSCFG0_DRAM_SIZE_8M:
+		ret = 8;
+		break;
+	case RT5350_SYSCFG0_DRAM_SIZE_16M:
+		ret = 16;
+		break;
+	case RT5350_SYSCFG0_DRAM_SIZE_32M:
+		ret = 32;
+		break;
+	case RT5350_SYSCFG0_DRAM_SIZE_64M:
+		ret = 64;
+		break;
+	default:
+		panic("rt5350: invalid DRAM size: %u", t);
+		break;
+	}
+
+	return ret;
+}
+
 void __init ralink_clk_init(void)
 {
 	unsigned long cpu_rate, sys_rate, wdt_rate, uart_rate;
@@ -252,4 +286,15 @@ void prom_soc_init(struct ralink_soc_info *soc_info)
 		name,
 		(id >> CHIP_ID_ID_SHIFT) & CHIP_ID_ID_MASK,
 		(id & CHIP_ID_REV_MASK));
+
+	soc_info->mem_base = RT305X_SDRAM_BASE;
+	if (soc_is_rt5350()) {
+		soc_info->mem_size = rt5350_get_mem_size();
+	} else if (soc_is_rt305x() || soc_is_rt3350()) {
+		soc_info->mem_size_min = RT305X_MEM_SIZE_MIN;
+		soc_info->mem_size_max = RT305X_MEM_SIZE_MAX;
+	} else if (soc_is_rt3352()) {
+		soc_info->mem_size_min = RT3352_MEM_SIZE_MIN;
+		soc_info->mem_size_max = RT3352_MEM_SIZE_MAX;
+	}
 }