armv7/exynos: Fix and remove memory reset workarounds

The memory corruption problem in Exynos suspend/resume process is caused by two
things together: PHY_RESET and MRS command.

After stop sending MRS on resume, we can now remove the workaround of skipping
PHY_RESET.

Change-Id: I64acc27c1d2bb549ae6ad7d32ecda94b0355972c
Reviewed-on: https://gerrit.chromium.org/gerrit/64736
Tested-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Commit-Queue: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: http://review.coreboot.org/4433
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/cpu/samsung/exynos5250/dmc_init_ddr3.c

@@ -158,8 +158,14 @@ int ddr3_mem_ctrl_init(struct mem_timings *mem, unsigned long mem_iv_size,
 	/* Send PALL command */
 	dmc_config_prech(mem, dmc);
 
-	/* Send NOP, MRS and ZQINIT commands */
+	if (mem_reset) {
+		/* Send NOP, MRS and ZQINIT commands.
+		 * Sending MRS command will reset the DRAM. We should not be
+		 * reseting the DRAM after resume, this will lead to memory
+		 * corruption as DRAM content is lost after DRAM reset
+		 */
 		dmc_config_mrs(mem, dmc);
+	}
 
 	if (mem->gate_leveling_enable) {
 		val = PHY_CON0_RESET_VAL;

src/cpu/samsung/exynos5420/dmc_init_ddr3.c

@@ -184,9 +184,15 @@ int ddr3_mem_ctrl_init(struct mem_timings *mem, int interleave_size, int reset)
 	writel(mem->timing_power, &drex0->timingpower);
 	writel(mem->timing_power, &drex1->timingpower);
 
-	/* Send NOP, MRS and ZQINIT commands */
+	/* Send NOP, MRS and ZQINIT commands.
+	 * Sending MRS command will reset the DRAM. We should not be
+	 * reseting the DRAM after resume, this will lead to memory
+	 * corruption as DRAM content is lost after DRAM reset.
+	 */
+	if (reset) {
 		dmc_config_mrs(mem, drex0);
 		dmc_config_mrs(mem, drex1);
+	}
 
 	if (mem->gate_leveling_enable) {
 

src/mainboard/google/snow/romstage.c

@@ -141,13 +141,6 @@ static void setup_memory(struct mem_timings *mem, int is_resume)
 	       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");
 	}