lib: Rewrite qemu-armv7 ramdetect

* Move armv7 RAM dection to a common place
* Enable it for all emulated platforms
* Use 32bit probe values and restore memory even on failure
* Use the new logic on the following boards:
** qemu-armv7
** qemu-riscv

Tested on qemu-system-riscv:
Fixes kernel panic due to wrong memory limits reported.

Change-Id: I37386c6a95bfc3b7b25aeae32c6e14cff9913513
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33934
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/lib/ramdetect.c

@@ -0,0 +1,78 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <types.h>
+#include <symbols.h>
+#include <device/mmio.h>
+#include <ramdetect.h>
+#include <console/console.h>
+
+#define OVERLAP(a, b, s, e) ((b) > (s) && (a) < (e))
+
+static int probe_mb(const uintptr_t dram_start, const uintptr_t size)
+{
+	uintptr_t addr = dram_start + (size * MiB) - sizeof(uint32_t);
+	static const uint32_t patterns[] = {
+		0x55aa55aa,
+		0x12345678
+	};
+	void *ptr = (void *) addr;
+	size_t i;
+
+	/* Don't accidentally clober oneself. */
+	if (OVERLAP(addr, addr + sizeof(uint32_t), (uintptr_t)_program, (uintptr_t) _eprogram))
+		return 1;
+
+	uint32_t old = read32(ptr);
+	for (i = 0; i < ARRAY_SIZE(patterns); i++) {
+		write32(ptr, patterns[i]);
+		if (read32(ptr) != patterns[i])
+			break;
+	}
+
+	write32(ptr, old);
+	return i == ARRAY_SIZE(patterns);
+}
+
+/* - 20 as probe_size is in MiB, - 1 as i is signed */
+#define MAX_ADDRESSABLE_SPACE (sizeof(size_t) * 8 - 20 - 1)
+
+/* Probe an area if it's read/writable. */
+size_t probe_ramsize(const uintptr_t dram_start, const size_t probe_size)
+{
+	ssize_t i;
+	size_t msb = 0;
+	size_t discovered = 0;
+
+	static size_t saved_result;
+	if (saved_result)
+		return saved_result;
+
+	/* Find the MSB + 1. */
+	size_t tmp = probe_size;
+	do {
+		msb++;
+	} while (tmp >>= 1);
+
+	/* Limit search to accessible address space */
+	msb = MIN(msb, MAX_ADDRESSABLE_SPACE);
+
+	/* Compact binary search.  */
+	for (i = msb; i >= 0; i--)
+		if (probe_mb(dram_start, (discovered | (1ULL << i))))
+			discovered |= (1ULL << i);
+
+	saved_result = discovered;
+	printk(BIOS_DEBUG, "RAMDETECT: Found %zu MiB RAM\n", discovered);
+	return discovered;
+}