soc/mediatek/mt8186: Set RTC capid to 0xC0 to pass XTAL 26 MHz test

The XTAL 26MHz test failed on krabby, so we adjust RTC capid from
default value 0x88 to 0xC0 for MT8186. We also add a new log message
to show the capid value which is read from MT6366.

This implementation is according to chapter 5.13 in MT8186 Functional
Specification.

BUG=b:218439447
TEST=set capid to 0xc0.
TEST=XTAL 26MHz test passed.

Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Change-Id: I16ab46a5697d304e8001de231ffc9b7b7a2f9282
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62290
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

src/soc/mediatek/mt8186/include/soc/rtc.h

@@ -143,6 +143,7 @@ enum {
 	PMIC_RG_DCXO_CW00	= 0x0788,
 	PMIC_RG_DCXO_CW00_CLR	= 0x078C,
 	PMIC_RG_DCXO_CW02	= 0x0790,
+	PMIC_RG_DCXO_CW03	= 0x0794,
 	PMIC_RG_DCXO_CW07	= 0x079A,
 	PMIC_RG_DCXO_CW09	= 0x079E,
 	PMIC_RG_DCXO_CW11	= 0x07A2,

src/soc/mediatek/mt8186/rtc.c

@@ -13,6 +13,8 @@
 #include <soc/pmic_wrap.h>
 #include <timer.h>
 
+#define MT8186_RTC_DXCO_CAPID 0xC0
+
 /* Initialize RTC setting of using DCXO clock */
 static bool rtc_enable_dcxo(void)
 {
@@ -231,6 +233,16 @@ static void mt6366_dcxo_disable_unused(void)
 	rtc_write(PMIC_RG_DCXO_CW23, 0x0052);
 }
 
+static void rtc_set_capid(u16 capid)
+{
+	u16 read_capid;
+
+	rtc_write(PMIC_RG_DCXO_CW03, 0xFF00 | capid);
+
+	rtc_read(PMIC_RG_DCXO_CW03, &read_capid);
+	rtc_info("read back capid: %#x\n", read_capid & 0xFF);
+}
+
 /* Check RTC Initialization */
 int rtc_init(int recover)
 {
@@ -337,6 +349,8 @@ static void dcxo_init(void)
 	rtc_write(PMIC_RG_DCXO_CW09, 0x408F);
 	mdelay(5);
 
+	rtc_set_capid(MT8186_RTC_DXCO_CAPID);
+
 	mt6366_dcxo_disable_unused();
 }