hw/timer/bcm2835: Support the timer COMPARE registers

This peripheral has 1 free-running timer and 4 compare registers.

Only the free-running timer is implemented. Add support the
COMPARE registers (each register is wired to an IRQ).

Reference: "BCM2835 ARM Peripherals" datasheet [*]
            chapter 12 "System Timer":

  The System Timer peripheral provides four 32-bit timer channels
  and a single 64-bit free running counter. Each channel has an
  output compare register, which is compared against the 32 least
  significant bits of the free running counter values. When the
  two values match, the system timer peripheral generates a signal
  to indicate a match for the appropriate channel. The match signal
  is then fed into the interrupt controller.

This peripheral is used since Linux 3.7, commit ee4af5696720
("ARM: bcm2835: add system timer").

[*] https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf



Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Message-id: 20201010203709.3116542-4-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/timer/bcm2835_systmr.c

@@ -28,20 +28,13 @@ REG32(COMPARE1,     0x10)
 REG32(COMPARE2,     0x14)
 REG32(COMPARE3,     0x18)
 
-static void bcm2835_systmr_update_irq(BCM2835SystemTimerState *s)
+static void bcm2835_systmr_timer_expire(void *opaque)
 {
-    bool enable = !!s->reg.ctrl_status;
+    BCM2835SystemTimerCompare *tmr = opaque;
 
-    trace_bcm2835_systmr_irq(enable);
-    qemu_set_irq(s->irq, enable);
-}
-
-static void bcm2835_systmr_update_compare(BCM2835SystemTimerState *s,
-                                          unsigned timer_index)
-{
-    /* TODO fow now, since neither Linux nor U-boot use these timers. */
-    qemu_log_mask(LOG_UNIMP, "COMPARE register %u not implemented\n",
-                  timer_index);
+    trace_bcm2835_systmr_timer_expired(tmr->id);
+    tmr->state->reg.ctrl_status |= 1 << tmr->id;
+    qemu_set_irq(tmr->irq, 1);
 }
 
 static uint64_t bcm2835_systmr_read(void *opaque, hwaddr offset,
@@ -75,19 +68,33 @@ static uint64_t bcm2835_systmr_read(void *opaque, hwaddr offset,
 }
 
 static void bcm2835_systmr_write(void *opaque, hwaddr offset,
-                                 uint64_t value, unsigned size)
+                                 uint64_t value64, unsigned size)
 {
     BCM2835SystemTimerState *s = BCM2835_SYSTIMER(opaque);
+    int index;
+    uint32_t value = value64;
+    uint32_t triggers_delay_us;
+    uint64_t now;
 
     trace_bcm2835_systmr_write(offset, value);
     switch (offset) {
     case A_CTRL_STATUS:
         s->reg.ctrl_status &= ~value; /* Ack */
-        bcm2835_systmr_update_irq(s);
+        for (index = 0; index < ARRAY_SIZE(s->tmr); index++) {
+            if (extract32(value, index, 1)) {
+                trace_bcm2835_systmr_irq_ack(index);
+                qemu_set_irq(s->tmr[index].irq, 0);
+            }
+        }
         break;
     case A_COMPARE0 ... A_COMPARE3:
-        s->reg.compare[(offset - A_COMPARE0) >> 2] = value;
-        bcm2835_systmr_update_compare(s, (offset - A_COMPARE0) >> 2);
+        index = (offset - A_COMPARE0) >> 2;
+        s->reg.compare[index] = value;
+        now = qemu_clock_get_us(QEMU_CLOCK_VIRTUAL);
+        /* Compare lower 32-bits of the free-running counter. */
+        triggers_delay_us = value - now;
+        trace_bcm2835_systmr_run(index, triggers_delay_us);
+        timer_mod(&s->tmr[index].timer, now + triggers_delay_us);
         break;
     case A_COUNTER_LOW:
     case A_COUNTER_HIGH:
@@ -125,7 +132,14 @@ static void bcm2835_systmr_realize(DeviceState *dev, Error **errp)
     memory_region_init_io(&s->iomem, OBJECT(dev), &bcm2835_systmr_ops,
                           s, "bcm2835-sys-timer", 0x20);
     sysbus_init_mmio(SYS_BUS_DEVICE(dev), &s->iomem);
-    sysbus_init_irq(SYS_BUS_DEVICE(dev), &s->irq);
+
+    for (size_t i = 0; i < ARRAY_SIZE(s->tmr); i++) {
+        s->tmr[i].id = i;
+        s->tmr[i].state = s;
+        sysbus_init_irq(SYS_BUS_DEVICE(dev), &s->tmr[i].irq);
+        timer_init_us(&s->tmr[i].timer, QEMU_CLOCK_VIRTUAL,
+                      bcm2835_systmr_timer_expire, &s->tmr[i]);
+    }
 }
 
 static const VMStateDescription bcm2835_systmr_vmstate = {

hw/timer/trace-events

@@ -77,9 +77,11 @@ nrf51_timer_write(uint8_t timer_id, uint64_t addr, uint32_t value, unsigned size
 nrf51_timer_set_count(uint8_t timer_id, uint8_t counter_id, uint32_t value) "timer %u counter %u count 0x%" PRIx32
 
 # bcm2835_systmr.c
-bcm2835_systmr_irq(bool enable) "timer irq state %u"
+bcm2835_systmr_timer_expired(unsigned id) "timer #%u expired"
+bcm2835_systmr_irq_ack(unsigned id) "timer #%u acked"
 bcm2835_systmr_read(uint64_t offset, uint64_t data) "timer read: offset 0x%" PRIx64 " data 0x%" PRIx64
-bcm2835_systmr_write(uint64_t offset, uint64_t data) "timer write: offset 0x%" PRIx64 " data 0x%" PRIx64
+bcm2835_systmr_write(uint64_t offset, uint32_t data) "timer write: offset 0x%" PRIx64 " data 0x%" PRIx32
+bcm2835_systmr_run(unsigned id, uint64_t delay_us) "timer #%u expiring in %"PRIu64" us"
 
 # avr_timer16.c
 avr_timer16_read(uint8_t addr, uint8_t value) "timer16 read addr:%u value:%u"

include/hw/timer/bcm2835_systmr.h

@@ -11,6 +11,7 @@
 
 #include "hw/sysbus.h"
 #include "hw/irq.h"
+#include "qemu/timer.h"
 #include "qom/object.h"
 
 #define TYPE_BCM2835_SYSTIMER "bcm2835-sys-timer"
@@ -18,18 +19,24 @@ OBJECT_DECLARE_SIMPLE_TYPE(BCM2835SystemTimerState, BCM2835_SYSTIMER)
 
 #define BCM2835_SYSTIMER_COUNT 4
 
+typedef struct {
+    unsigned id;
+    QEMUTimer timer;
+    qemu_irq irq;
+    BCM2835SystemTimerState *state;
+} BCM2835SystemTimerCompare;
+
 struct BCM2835SystemTimerState {
     /*< private >*/
     SysBusDevice parent_obj;
 
     /*< public >*/
     MemoryRegion iomem;
-    qemu_irq irq;
-
     struct {
         uint32_t ctrl_status;
         uint32_t compare[BCM2835_SYSTIMER_COUNT];
     } reg;
+    BCM2835SystemTimerCompare tmr[BCM2835_SYSTIMER_COUNT];
 };
 
 #endif