Google/Snow: Temporary fix for resume failure.

The DDR3 memory initialization (with "mem_reset" set on normal boot) will cause
resume to be unstable, especially when X is running. System may show X screen
for few seconds, then crash randomly and unable to recover - although text
console may still work for a while.  Probably caused by corrupted memory pages.

'mem_reset' (which refers to RESET# in DDR3 spec) should be enabled according
to DDR3 spec. But it seems that on Exynos 5, memory can be initialized without
setting mem_reset for both normal boot and resume - at least no known failure
cases are found yet.  So this can be a temporary workaround.

Verified by booting a Google/Snow device with X Window and ChromeOS, entering
browser session with fancy web pages, closing LID to suspend for 5 seconds, then
re-opening to resume.  Suspend/resume worked as expected.

Also tried the "suspend_stress_test" with X running and finished 100 iterations
of suspend/resume test without failure.

Change-Id: I7185b362ce8b545fe77b35a552245736c89d465e
Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: http://review.coreboot.org/3148
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/google/snow/romstage.c

@@ -150,6 +150,14 @@ static void snow_setup_memory(struct mem_timings *mem, int is_resume)
 	       mem->mem_type,
 	       mem->mpll_mdiv,
 	       mem->frequency_mhz);
+
+	/* FIXME Currently memory initialization with mem_reset on normal boot
+	 * will cause resume to fail (even if we don't do mem_reset on resume),
+	 * and the workaround is to temporarily always enable "is_resume".
+	 * This should be removed when the root cause of resume issue is found.
+	 */
+	is_resume = 1;
+
 	if (ddr3_mem_ctrl_init(mem, DMC_INTERLEAVE_SIZE, !is_resume)) {
 		die("Failed to initialize memory controller.\n");
 	}