target/linux/ramips/patches-5.4/325-mt7621-fix-memory-detect.patch

--- a/arch/mips/ralink/mt7621.c
+++ b/arch/mips/ralink/mt7621.c
@@ -58,7 +58,9 @@
 #define MT7621_GPIO_MODE_SDHCI_SHIFT	18
 #define MT7621_GPIO_MODE_SDHCI_GPIO	1
 
-static void *detect_magic __initdata = detect_memory_region;
+#define MT7621_MEM_TEST_PATTERN         0xaa5555aa
+
+static u32 detect_magic __initdata;
 
 static struct rt2880_pmx_func uart1_grp[] =  { FUNC("uart1", 0, 1, 2) };
 static struct rt2880_pmx_func i2c_grp[] =  { FUNC("i2c", 0, 3, 2) };
@@ -144,26 +146,34 @@ static struct clk *__init mt7621_add_sys
 	return clk;
 }
 
+static bool __init mt7621_addr_wraparound_test(phys_addr_t size)
+{
+	void *dm = (void *)KSEG1ADDR(&detect_magic);
+	if (CPHYSADDR(dm + size) >= MT7621_LOWMEM_MAX_SIZE)
+		return true;
+	__raw_writel(MT7621_MEM_TEST_PATTERN, dm);
+	if (__raw_readl(dm) != __raw_readl(dm + size))
+		return false;
+	__raw_writel(!MT7621_MEM_TEST_PATTERN, dm);
+	return __raw_readl(dm) == __raw_readl(dm + size);
+}
+
 void __init mt7621_memory_detect(void)
 {
-	void *dm = &detect_magic;
 	phys_addr_t size;
 
-	for (size = 32 * SZ_1M; size < 256 * SZ_1M; size <<= 1) {
-		if (!__builtin_memcmp(dm, dm + size, sizeof(detect_magic)))
-			break;
+	for (size = 32 * SZ_1M; size <= 256 * SZ_1M; size <<= 1) {
+		if (mt7621_addr_wraparound_test(size)) {
+			add_memory_region(MT7621_LOWMEM_BASE, size, BOOT_MEM_RAM);
+			return;
+		}
 	}
 
-	if ((size == 256 * SZ_1M) &&
-	    (CPHYSADDR(dm + size) < MT7621_LOWMEM_MAX_SIZE) &&
-	    __builtin_memcmp(dm, dm + size, sizeof(detect_magic))) {
-		add_memory_region(MT7621_LOWMEM_BASE, MT7621_LOWMEM_MAX_SIZE,
-				  BOOT_MEM_RAM);
-		add_memory_region(MT7621_HIGHMEM_BASE, MT7621_HIGHMEM_SIZE,
-				  BOOT_MEM_RAM);
-	} else {
-		add_memory_region(MT7621_LOWMEM_BASE, size, BOOT_MEM_RAM);
-	}
+	/* addr doesn't wrap around at dm + 256M, assume 512M memory. */
+	add_memory_region(MT7621_LOWMEM_BASE, MT7621_LOWMEM_MAX_SIZE,
+			  BOOT_MEM_RAM);
+	add_memory_region(MT7621_HIGHMEM_BASE, MT7621_HIGHMEM_SIZE,
+			  BOOT_MEM_RAM);
 }
 
 void __init ralink_clk_init(void)