mediatek: Use the 64-bit timer

GPT4 is a 32-bit timer and the counter of GPT4 will overflow in about
330 seconds (0xffffffff / 13MHz). Timer and delay functions will not
work properly if the counter overflows. To fix that we should use the
64-bit timer (GPT6).

BUG=b:80501386
BRANCH=none
Test=emerge-elm coreboot; emerge-kukui coreboot

Change-Id: I9f080e47253a1b1bab4636a45cb86c8666a25302
Signed-off-by: Tristan Shieh <tristan.shieh@mediatek.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32245
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: You-Cheng Syu <youcheng@google.com>

1 files changed, 20 insertions, 7 deletions

diff --git a/src/soc/mediatek/common/timer.c b/src/soc/mediatek/common/timer.c
index 0762c2b4b4..c8af2be113 100644
--- a/src/soc/mediatek/common/timer.c
+++ b/src/soc/mediatek/common/timer.c
@@ -25,21 +25,34 @@ static struct mtk_gpt_regs *const mtk_gpt = (void *)GPT_BASE;
 
 __weak void timer_prepare(void) { /* do nothing */ }
 
+static uint64_t timer_raw_value(void)
+{
+	/*
+	 * According to "General-Purpose Timer (GPT).pdf", The read operation of
+	 * gpt6_cnt_l will make gpt6_cnt_h fixed until the next read operation
+	 * of gpt6_cnt_l. Therefore, we must read gpt6_cnt_l before gpt6_cnt_h.
+	 */
+	uint32_t low = read32(&mtk_gpt->gpt6_cnt_l);
+	uint32_t high = read32(&mtk_gpt->gpt6_cnt_h);
+
+	return low | (uint64_t)high << 32;
+}
+
 void timer_monotonic_get(struct mono_time *mt)
 {
-	mono_time_set_usecs(mt, read32(&mtk_gpt->gpt4_cnt) / GPT4_MHZ);
+	mono_time_set_usecs(mt, timer_raw_value() / GPT_MHZ);
 }
 
 void init_timer(void)
 {
 	timer_prepare();
 
-	/* Disable GPT4 and clear the counter */
-	clrbits_le32(&mtk_gpt->gpt4_con, GPT_CON_EN);
-	setbits_le32(&mtk_gpt->gpt4_con, GPT_CON_CLR);
+	/* Disable timer and clear the counter */
+	clrbits_le32(&mtk_gpt->gpt6_con, GPT_CON_EN);
+	setbits_le32(&mtk_gpt->gpt6_con, GPT_CON_CLR);
 
 	/* Set clock source to system clock and set clock divider to 1 */
-	write32(&mtk_gpt->gpt4_clk, GPT_SYS_CLK | GPT_CLK_DIV1);
-	/* Set operation mode to FREERUN mode and enable GTP4 */
-	write32(&mtk_gpt->gpt4_con, GPT_CON_EN | GPT_MODE_FREERUN);
+	write32(&mtk_gpt->gpt6_clk, GPT_SYS_CLK | GPT_CLK_DIV1);
+	/* Set operation mode to FREERUN mode and enable timer */
+	write32(&mtk_gpt->gpt6_con, GPT_CON_EN | GPT_MODE_FREERUN);
 }