qemu/vexpress-a9: Discover RAM size.

Probe RAM to find its size instead of hardcoding 1024M.
Also properly export it to memory map.

Change-Id: Ib411f0a068bd247a9e0cd0a59689a3896921483e
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: https://review.coreboot.org/13754
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

1 files changed, 45 insertions, 1 deletions

diff --git a/src/mainboard/emulation/qemu-armv7/cbmem.c b/src/mainboard/emulation/qemu-armv7/cbmem.c
index a626ec6adf..f26ca6cd20 100644
--- a/src/mainboard/emulation/qemu-armv7/cbmem.c
+++ b/src/mainboard/emulation/qemu-armv7/cbmem.c
@@ -14,8 +14,52 @@
 #include <stddef.h>
 #include <cbmem.h>
 #include <symbols.h>
+#include <arch/io.h>
+#include "mainboard.h"
+
+#define PATTERN1 0x55
+#define PATTERN2 0xaa
+
+/* Returns 1 if mebibyte mb is present and 0 otherwise.  */
+static int probe_mb(int mb)
+{
+	char *ptr = (char *) 0x60000000 + (mb << 20) + 0xfffff;
+	char old;
+	if (ptr < (char *) &_eprogram) {
+		/* Don't probe below _end to avoid accidentally clobering
+		   oneself.  */
+		return 1;
+	}
+
+	old = read8(ptr);
+	write8(ptr, PATTERN1);
+	if (read8(ptr) != PATTERN1)
+		return 0;
+	write8(ptr, PATTERN2);
+	if (read8(ptr) != PATTERN2)
+		return 0;
+	write8(ptr, old);
+	return 1;
+}
+
+int probe_ramsize(void)
+{
+	int i;
+	int discovered = 0;
+	static int saved_result;
+	if (saved_result)
+		return saved_result;
+	/* Compact binary search.  */
+	/* 1 GiB is the largest supported RAM by this machine.  */
+	for (i = 9; i >= 0; i--)
+		if (probe_mb(discovered | (1 << i)))
+			discovered |= (1 << i);
+	discovered++;
+	saved_result = discovered;
+	return discovered;
+}
 
 void *cbmem_top(void)
 {
-	return _dram + (CONFIG_DRAM_SIZE_MB << 20);
+	return _dram + (probe_ramsize() << 20);
 }