[PATCH v3 2/2] sunxi: restore modified memory

[Andrey Skvortsov]

Current sunxi DRAM initialisation code does several test accesses to the
DRAM array to detect aliasing effects and so determine the correct
row/column configuration. This changes the DRAM content, which breaks
use cases like soft reset and Linux's ramoops mechanism.

Fix this problem by saving and restoring the content of the DRAM cells
that is used for the test writes.

Signed-off-by: Andrey Skvortsov <andrej.skvortzov at gmail.com>
---
 arch/arm/mach-sunxi/dram_helpers.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mach-sunxi/dram_helpers.c b/arch/arm/mach-sunxi/dram_helpers.c
index 661186b648..e487f87bf3 100644
--- a/arch/arm/mach-sunxi/dram_helpers.c
+++ b/arch/arm/mach-sunxi/dram_helpers.c
@@ -32,13 +32,25 @@ void mctl_await_completion(u32 *reg, u32 mask, u32 val)
 #ifndef CONFIG_MACH_SUNIV
 bool mctl_mem_matches_base(u32 offset, ulong base)
 {
+	u32 val_base;
+	u32 val_offset;
+	bool ret;
+
+	/* Save original values */
+	val_base = readl(base);
+	val_offset = readl(base + offset);
+
 	/* Try to write different values to RAM at two addresses */
 	writel(0, base);
 	writel(0xaa55aa55, base + offset);
 	dsb();
 	/* Check if the same value is actually observed when reading back */
-	return readl(base) ==
-	       readl(base + offset);
+	ret = readl(base) == readl(base + offset);
+
+	/* Restore original values */
+	writel(val_base, base);
+	writel(val_offset, base + offset);
+	return ret;
 }
 
 /*
-- 
2.42.0