soc/mediatek/mt8196: Set RTC EOSC calibration to 8 seconds

Set the RTC EOSC (External Oscillator) calibration to 8 seconds in
rtc_boot flow to ensure the accuracy of the RTC time during long period
of suspend. Without this setting, default value is 0, meaning no EOSC
calibration.

BRANCH=rauru
BUG=b:441304060
TEST=emerge-rauru coreboot chromeos-bootimage, when suspend/
warmboot/coldboot, RTC boots and works normally.

Signed-off-by: Shunxi Zhang <ot_shunxi.zhang@mediatek.corp-partner.google.com>
Change-Id: Ia7f15a6056cfa6bd808bc5a91147c1d64aff1223
Reviewed-on: https://review.coreboot.org/c/coreboot/+/89307
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Yidi Lin <yidilin@google.com>

src/soc/mediatek/mt8196/include/soc/mt6685_rtc.h

@@ -120,6 +120,8 @@
 #define RTC_K_EOSC_RSV_1		(1 << 9)
 #define RTC_K_EOSC_RSV_2		(1 << 10)
 
+#define RTC_EOSC_CALI_TD_8SEC		(6 << 8)
+
 #define TMA_KEY				0x39e
 #define TMA_KEY_MASK			0xFF
 #define TMA_KEY_SHIFT			0

src/soc/mediatek/mt8196/mt6685_rtc.c

@@ -570,6 +570,11 @@ void rtc_boot(void)
 		}
 	}
 
+	/* Set RTC EOSC calibration period = 8sec */
+	rtc_read(RTC_AL_DOW, &rdata);
+	rtc_write(RTC_AL_DOW, rdata | RTC_EOSC_CALI_TD_8SEC);
+	rtc_write_trigger();
+
 	/* Make sure RTC get the latest register info. */
 	rtc_read(RTC_BBPU, &rtc_bbpu);
 	rtc_write(RTC_BBPU, rtc_bbpu | RTC_BBPU_KEY | RTC_BBPU_RELOAD);