northbridge/amd/amdmct: Skip DCT config write to Flash if unchanged

Change-Id: I5fee5f5fdf30ab6e3c4f94ed3e54ea66c1204352
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: http://review.coreboot.org/11980
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: Raptor Engineering Automated Test Stand <noreply@raptorengineeringinc.com>

3 files changed, 23 insertions, 2 deletions

diff --git a/src/northbridge/amd/amdmct/mct_ddr3/mct_d.c b/src/northbridge/amd/amdmct/mct_ddr3/mct_d.c
index 1d48070084..2d8ab34c61 100644
--- a/src/northbridge/amd/amdmct/mct_ddr3/mct_d.c
+++ b/src/northbridge/amd/amdmct/mct_ddr3/mct_d.c
@@ -1368,6 +1368,7 @@ restartinit:
 		printk(BIOS_DEBUG, "mctAutoInitMCT_D: Restoring DCT configuration from NVRAM\n");
 		if (restore_mct_information_from_nvram(0) != 0)
 			printk(BIOS_CRIT, "%s: ERROR: Unable to restore DCT configuration from NVRAM\n", __func__);
+		pMCTstat->GStatus |= 1 << GSB_ConfigRestored;
 #endif
 
 		printk(BIOS_DEBUG, "mctAutoInitMCT_D: mct_ForceNBPState0_Dis_Fam15\n");
@@ -2095,6 +2096,8 @@ static void DQSTiming_D(struct MCTStatStruc *pMCTstat,
 
 		if (is_fam15h())
 			exit_training_mode_fam15(pMCTstat, pDCTstatA);
+
+		pMCTstat->GStatus |= 1 << GSB_ConfigRestored;
 	}
 
 	/* FIXME - currently uses calculated value	TrainMaxReadLatency_D(pMCTstat, pDCTstatA); */
diff --git a/src/northbridge/amd/amdmct/mct_ddr3/mct_d.h b/src/northbridge/amd/amdmct/mct_ddr3/mct_d.h
index 1ac7bbfe62..196d96d083 100644
--- a/src/northbridge/amd/amdmct/mct_ddr3/mct_d.h
+++ b/src/northbridge/amd/amdmct/mct_ddr3/mct_d.h
@@ -312,6 +312,7 @@ struct MCTStatStruc {
 #define GSB_SpIntRemapHole	16	/* Special condition for Node Interleave and HW remapping*/
 #define GSB_EnDIMMSpareNW	17	/* Indicates that DIMM Spare can be used without a warm reset */
 					/* NOTE: This is a local bit used by memory code */
+#define GSB_ConfigRestored	18	/* Training configuration was restored from NVRAM */
 
 /*===============================================================================
 	Local DCT Status structure (a structure for each DCT)
diff --git a/src/northbridge/amd/amdmct/mct_ddr3/s3utils.c b/src/northbridge/amd/amdmct/mct_ddr3/s3utils.c
index 8ed7e3ce87..0a508cb406 100644
--- a/src/northbridge/amd/amdmct/mct_ddr3/s3utils.c
+++ b/src/northbridge/amd/amdmct/mct_ddr3/s3utils.c
@@ -209,7 +209,7 @@ static uint32_t read_config32_dct_nbpstate(device_t dev, uint8_t node, uint8_t d
 	return pci_read_config32(dev, reg);
 }
 
-static void copy_cbmem_spd_data_to_save_variable(struct amd_s3_persistent_data* persistent_data)
+static void copy_cbmem_spd_data_to_save_variable(struct amd_s3_persistent_data* persistent_data, uint8_t * restored)
 {
 	uint8_t node;
 	uint8_t dimm;
@@ -232,6 +232,13 @@ static void copy_cbmem_spd_data_to_save_variable(struct amd_s3_persistent_data*
 	for (node = 0; node < MAX_NODES_SUPPORTED; node++)
 		for (channel = 0; channel < 2; channel++)
 			persistent_data->node[node].memclk[channel] = mem_info->dct_stat[node].Speed;
+
+	if (restored) {
+		if (mem_info->mct_stat.GStatus & (1 << GSB_ConfigRestored))
+			*restored = 1;
+		else
+			*restored = 0;
+	}
 }
 
 void copy_mct_data_to_save_variable(struct amd_s3_persistent_data* persistent_data)
@@ -1030,6 +1037,7 @@ void restore_mct_data_from_save_variable(struct amd_s3_persistent_data* persiste
 int8_t save_mct_information_to_nvram(void)
 {
 	uint8_t nvram;
+	uint8_t restored = 0;
 
 	if (acpi_is_wakeup_s3())
 		return 0;
@@ -1051,7 +1059,16 @@ int8_t save_mct_information_to_nvram(void)
 	copy_mct_data_to_save_variable(persistent_data);
 
 	/* Save RAM SPD data at the same time */
-	copy_cbmem_spd_data_to_save_variable(persistent_data);
+	copy_cbmem_spd_data_to_save_variable(persistent_data, &restored);
+
+	if (restored) {
+		/* Allow training bypass if DIMM configuration is unchanged on next boot */
+		nvram = 1;
+		set_option("allow_spd_nvram_cache_restore", &nvram);
+
+		printk(BIOS_DEBUG, "Hardware configuration unchanged since last boot; skipping write\n");
+		return 0;
+	}
 
 	/* Obtain CBFS file offset */
 	s3nv_offset = get_s3nv_file_offset();