soc/intel/skylake: refactor rtc failure checking

In order to prepare for checking RTC failure in the early boot
paths move the rtc failure calculation to pmutil.c and add a helper
function to determine if failure occurred.

BUG=b:63054105

Change-Id: I88bf9bdba8c1f3a11bc8301869e3da9f033ec381
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/21554
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/skylake/include/soc/pm.h

@@ -193,6 +193,9 @@ void pmc_set_disb(void);
 /* Initialize GPEs */
 void pmc_gpe_init(void);
 
+/* Return non-zero when RTC failure happened. */
+int rtc_failure(void);
+
 static inline int deep_s3_enabled(void)
 {
 	uint32_t deep_s3_pol;

src/soc/intel/skylake/pmc.c

@@ -107,22 +107,10 @@ static void pch_set_acpi_mode(void)
 
 static void pch_rtc_init(void)
 {
-	u8 reg8;
-	int rtc_failed;
-	/*PMC Controller Device 0x1F, Func 02*/
-	device_t dev = PCH_DEV_PMC;
-	reg8 = pci_read_config8(dev, GEN_PMCON_B);
-	rtc_failed = reg8 & RTC_BATTERY_DEAD;
-	if (rtc_failed) {
-		reg8 &= ~RTC_BATTERY_DEAD;
-		pci_write_config8(dev, GEN_PMCON_B, reg8);
-		printk(BIOS_DEBUG, "rtc_failed = 0x%x\n", rtc_failed);
-	}
-
 	/* Ensure the date is set including century byte. */
 	cmos_check_update_date();
 
-	cmos_init(rtc_failed);
+	cmos_init(rtc_failure());
 }
 
 static void pch_power_options(void)

src/soc/intel/skylake/pmutil.c

@@ -541,3 +541,20 @@ void pmc_gpe_init(void)
 	enable_all_gpe(config->gpe0_en_1, config->gpe0_en_2,
 			config->gpe0_en_3, config->gpe0_en_4);
 }
+
+int rtc_failure(void)
+{
+	u8 reg8;
+	int rtc_failed;
+	/* PMC Controller Device 0x1F, Func 02 */
+	device_t dev = PCH_DEV_PMC;
+	reg8 = pci_read_config8(dev, GEN_PMCON_B);
+	rtc_failed = reg8 & RTC_BATTERY_DEAD;
+	if (rtc_failed) {
+		reg8 &= ~RTC_BATTERY_DEAD;
+		pci_write_config8(dev, GEN_PMCON_B, reg8);
+		printk(BIOS_DEBUG, "rtc_failed = 0x%x\n", rtc_failed);
+	}
+
+	return !!rtc_failed;
+}