soc/ti/am335x: Fix timer implementation

Implements the monotonic timer using the am335x dmtimer peripheral.

Change-Id: I4736b6d3b6e26370be9e8f369fc02285ad519223
Signed-off-by: Sam Lewis <sam.vr.lewis@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44383
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/ti/am335x/Makefile.inc

@@ -1,18 +1,15 @@
 ifeq ($(CONFIG_SOC_TI_AM335X),y)
 bootblock-y	+= bootblock.c
 bootblock-y	+= bootblock_media.c
-bootblock-y	+= dmtimer.c
+bootblock-y	+= timer.c
 bootblock-y	+= gpio.c
 bootblock-y	+= pinmux.c
-bootblock-y	+= monotonic_timer.c
 
 romstage-y	+= nand.c
 romstage-y	+= cbmem.c
-romstage-y	+= dmtimer.c
-romstage-y	+= monotonic_timer.c
+romstage-y	+= timer.c
 
-ramstage-y	+= dmtimer.c
-ramstage-y	+= monotonic_timer.c
+ramstage-y	+= timer.c
 ramstage-y	+= nand.c
 ramstage-y  += soc.c
 

src/soc/ti/am335x/dmtimer.c

@@ -1,12 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-
-#include "dmtimer.h"
-
-void dmtimer_start(int num)
-{
-}
-
-uint64_t dmtimer_raw_value(int num)
-{
-	return 0;
-}

src/soc/ti/am335x/dmtimer.h

@@ -5,9 +5,33 @@
 
 #include <stdint.h>
 
-#define OSC_HZ 24000000
+#define M_OSC_MHZ (24)
 
-void dmtimer_start(int num);
-uint64_t dmtimer_raw_value(int num);
+struct am335x_dmtimer {
+	uint32_t tidr;
+	uint8_t res1[12];
+	uint32_t tiocp_cfg;
+	uint8_t res2[12];
+	uint32_t irq_eoi;
+	uint32_t irqstatus_raw;
+	uint32_t irqstatus;
+	uint32_t irqenable_set;
+	uint32_t irqenable_clr;
+	uint32_t irqwakeen;
+	uint32_t tclr;
+	uint32_t tcrr;
+	uint32_t tldr;
+	uint32_t ttgr;
+	uint32_t twps;
+	uint32_t tmar;
+	uint32_t tcar1;
+	uint32_t tsicr;
+	uint32_t tcar2;
+};
+
+#define TCLR_ST (0x01 << 0)
+#define TCLR_AR (0x01 << 1)
+
+#define DMTIMER_2 (0x48040000)
 
 #endif

src/soc/ti/am335x/monotonic_timer.c

@@ -1,40 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-
-#include <stdint.h>
-#include <delay.h>
-#include <timer.h>
-
-#include "dmtimer.h"
-
-static struct monotonic_counter {
-	int initialized;
-	struct mono_time time;
-	uint64_t last_value;
-} mono_counter;
-
-static const uint32_t clocks_per_usec = OSC_HZ/1000000;
-
-void timer_monotonic_get(struct mono_time *mt)
-{
-	uint64_t current_tick;
-	uint64_t usecs_elapsed;
-
-	if (!mono_counter.initialized) {
-		init_timer();
-		mono_counter.last_value = dmtimer_raw_value(0);
-		mono_counter.initialized = 1;
-	}
-
-	current_tick = dmtimer_raw_value(0);
-	usecs_elapsed = (current_tick - mono_counter.last_value) /
-							clocks_per_usec;
-
-	/* Update current time and tick values only if a full tick occurred. */
-	if (usecs_elapsed) {
-		mono_time_add_usecs(&mono_counter.time, usecs_elapsed);
-		mono_counter.last_value = current_tick;
-	}
-
-	/* Save result. */
-	*mt = mono_counter.time;
-}

src/soc/ti/am335x/timer.c

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <timer.h>
+#include <delay.h>
+#include <device/mmio.h>
+
+#include "dmtimer.h"
+#include "clock.h"
+
+struct am335x_dmtimer *dmtimer_2 = (struct am335x_dmtimer *)DMTIMER_2;
+
+#define CLKSEL_M_OSC (0x01 << 0)
+
+static uint32_t timer_raw_value(void)
+{
+	return read32(&dmtimer_2->tcrr);
+}
+
+void timer_monotonic_get(struct mono_time *mt)
+{
+	mono_time_set_usecs(mt, timer_raw_value() / M_OSC_MHZ);
+}
+
+void init_timer(void)
+{
+	write32(&am335x_cm_dpll->clksel_timer2_clk, CLKSEL_M_OSC);
+
+	// Start the dmtimer in autoreload mode without any prescalers
+	// With M_OSC at 24MHz, this gives a few minutes before the timer overflows
+	write32(&dmtimer_2->tclr, TCLR_ST | TCLR_AR);
+}