[Qemu-devel] [PATCH] Added periodic IRQ support for bcm2836_control local timer

[bzt <bztemail@gmail.com>]

Dear qemu developers,

Honestly SubmitAPatch is a bit complicated for me, so I'm hoping I've
done everything right. To be sure, you can find my patch here:
https://github.com/bztsrc/qemu-local-timer and diff against the latest
github repo here:
https://github.com/bztsrc/qemu-local-timer/blob/patches/3.1.50.diff

Currently the IRQ_TIMER in bcm2836_control is defined, but not
implemented. This patch adds the basic functionality to qemu by
implementing 3 new registers in bcm2836_control. You can route the
interrupt to one of the cores' IRQ or FIQ line by writing 0x40000024,
and you can set up a periodic interrupt with 38.4MHz frequency by
writing the divider into 0x40000034. Prescaler are not taken into
account. When the IRQ fired, you'll see it in 0x40000040+4*N bit 11
with the rest of the local IRQs, and you can acknowledge it by writing
1<<31 to 0x40000038.

The patch is pretty simple, should be easy to review: it does not
create new classes, does not delete anything, does not change class
interface, and only two files modified, the bcm2836_control.c and it's
header.

Sign-off-by: Zoltán Baldaszti <bztemail@gmail.com>
Subject: [PATCH] Added periodic IRQ support for bcm2836_control local timer

diff --git a/hw/intc/bcm2836_control.c b/hw/intc/bcm2836_control.c
index cfa5bc7365..fbd31de0f1 100644
--- a/hw/intc/bcm2836_control.c
+++ b/hw/intc/bcm2836_control.c
@@ -7,7 +7,11 @@
  * This code is licensed under the GNU GPLv2 and later.
  *
  * At present, only implements interrupt routing, and mailboxes (i.e.,
- * not local timer, PMU interrupt, or AXI counters).
+ * not PMU interrupt, or AXI counters).
+ *
+ * 64-bit ARM Local Timer Copyright (c) 2019. Zoltán Baldaszti
+ * The IRQ_TIMER support is still very basic, does not handle timer access,
+ * and such there's no point in enabling it without the interrupt flag set.
  *
  * Ref:
  * https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2836/QA7_rev3.4.pdf
@@ -18,6 +22,9 @@
 #include "qemu/log.h"

 #define REG_GPU_ROUTE           0x0c
+#define REG_LOCALTIMERROUTING   0x24
+#define REG_LOCALTIMERCONTROL   0x34
+#define REG_LOCALTIMERACK       0x38
 #define REG_TIMERCONTROL        0x40
 #define REG_MBOXCONTROL         0x50
 #define REG_IRQSRC              0x60
@@ -43,6 +50,13 @@
 #define IRQ_TIMER       11
 #define IRQ_MAX         IRQ_TIMER

+#define LOCALTIMER_FREQ      38400000
+#define LOCALTIMER_INTFLAG   (1 << 31)
+#define LOCALTIMER_RELOAD    (1 << 30)
+#define LOCALTIMER_INTENABLE (1 << 29)
+#define LOCALTIMER_ENABLE    (1 << 28)
+#define LOCALTIMER_VALUE(x)  ((x) & 0xfffffff)
+
 static void deliver_local(BCM2836ControlState *s, uint8_t core, uint8_t irq,
                           uint32_t controlreg, uint8_t controlidx)
 {
@@ -78,6 +92,15 @@ static void bcm2836_control_update(BCM2836ControlState *s)
         s->fiqsrc[s->route_gpu_fiq] |= (uint32_t)1 << IRQ_GPU;
     }

+    /* handle THE local timer interrupt for one of the cores' IRQ/FIQ */
+    if (s->triggered) {
+        if (s->route_localtimer & 4) {
+            s->fiqsrc[(s->route_localtimer & 3)] |= (uint32_t)1 << IRQ_TIMER;
+        } else {
+            s->irqsrc[(s->route_localtimer & 3)] |= (uint32_t)1 << IRQ_TIMER;
+        }
+    }
+
     for (i = 0; i < BCM2836_NCORES; i++) {
         /* handle local timer interrupts for this core */
         if (s->timerirqs[i]) {
@@ -162,6 +185,62 @@ static void bcm2836_control_set_gpu_fiq(void
*opaque, int irq, int level)
     bcm2836_control_update(s);
 }

+static void bcm2836_control_local_timer_set_next(void *opaque)
+{
+    BCM2836ControlState *s = opaque;
+    uint64_t next_event;
+
+    assert(s->period > 0);
+
+    next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
+        (NANOSECONDS_PER_SECOND * s->period / LOCALTIMER_FREQ);
+    timer_mod(s->timer, next_event);
+}
+
+static void bcm2836_control_local_timer_tick(void *opaque)
+{
+    BCM2836ControlState *s = opaque;
+
+    bcm2836_control_local_timer_set_next(s);
+
+    if (!s->triggered) {
+        s->triggered = 1;
+        bcm2836_control_update(s);
+    }
+}
+
+static void bcm2836_control_local_timer_control(void *opaque, uint32_t val)
+{
+    BCM2836ControlState *s = opaque;
+
+    s->period = LOCALTIMER_VALUE(val);
+    if (val & LOCALTIMER_INTENABLE) {
+        if (!s->timer) {
+            s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
+                bcm2836_control_local_timer_tick, s);
+        }
+        bcm2836_control_local_timer_set_next(s);
+    } else {
+        if (s->timer) {
+            timer_del(s->timer);
+            s->timer = NULL;
+        }
+        s->triggered = 0;
+    }
+}
+
+static void bcm2836_control_local_timer_ack(void *opaque, uint32_t val)
+{
+    BCM2836ControlState *s = opaque;
+
+    if (val & LOCALTIMER_INTFLAG) {
+        s->triggered = 0;
+    }
+    if (val & LOCALTIMER_RELOAD) {
+        bcm2836_control_local_timer_set_next(s);
+    }
+}
+
 static uint64_t bcm2836_control_read(void *opaque, hwaddr offset,
unsigned size)
 {
     BCM2836ControlState *s = opaque;
@@ -170,6 +249,14 @@ static uint64_t bcm2836_control_read(void
*opaque, hwaddr offset, unsigned size)
         assert(s->route_gpu_fiq < BCM2836_NCORES
                && s->route_gpu_irq < BCM2836_NCORES);
         return ((uint32_t)s->route_gpu_fiq << 2) | s->route_gpu_irq;
+    } else if (offset == REG_LOCALTIMERROUTING) {
+        return s->route_localtimer;
+    } else if (offset == REG_LOCALTIMERCONTROL) {
+        return s->period |
+            (s->timer ? LOCALTIMER_ENABLE | LOCALTIMER_INTENABLE : 0) |
+            (s->triggered ? LOCALTIMER_INTFLAG : 0);
+    } else if (offset == REG_LOCALTIMERACK) {
+        return 0;
     } else if (offset >= REG_TIMERCONTROL && offset < REG_MBOXCONTROL) {
         return s->timercontrol[(offset - REG_TIMERCONTROL) >> 2];
     } else if (offset >= REG_MBOXCONTROL && offset < REG_IRQSRC) {
@@ -195,6 +282,12 @@ static void bcm2836_control_write(void *opaque,
hwaddr offset,
     if (offset == REG_GPU_ROUTE) {
         s->route_gpu_irq = val & 0x3;
         s->route_gpu_fiq = (val >> 2) & 0x3;
+    } else if (offset == REG_LOCALTIMERROUTING) {
+        s->route_localtimer = val & 7;
+    } else if (offset == REG_LOCALTIMERCONTROL) {
+        bcm2836_control_local_timer_control(s, val);
+    } else if (offset == REG_LOCALTIMERACK) {
+        bcm2836_control_local_timer_ack(s, val);
     } else if (offset >= REG_TIMERCONTROL && offset < REG_MBOXCONTROL) {
         s->timercontrol[(offset - REG_TIMERCONTROL) >> 2] = val & 0xff;
     } else if (offset >= REG_MBOXCONTROL && offset < REG_IRQSRC) {
@@ -227,6 +320,13 @@ static void bcm2836_control_reset(DeviceState *d)

     s->route_gpu_irq = s->route_gpu_fiq = 0;

+    s->route_localtimer = s->triggered = 0;
+    s->period = 0;
+    if(s->timer) {
+        timer_del(s->timer);
+        s->timer = NULL;
+    }
+
     for (i = 0; i < BCM2836_NCORES; i++) {
         s->timercontrol[i] = 0;
         s->mailboxcontrol[i] = 0;
diff --git a/include/hw/intc/bcm2836_control.h
b/include/hw/intc/bcm2836_control.h
index 613f3c4186..873bd52253 100644
--- a/include/hw/intc/bcm2836_control.h
+++ b/include/hw/intc/bcm2836_control.h
@@ -5,6 +5,9 @@
  * Rasperry Pi 2 emulation and refactoring Copyright (c) 2015, Microsoft
  * Written by Andrew Baumann
  *
+ * 64-bit ARM Local Timer Copyright (c) 2019. Zoltán Baldaszti
+ * Added basic IRQ_TIMER interrupt support
+ *
  * This code is licensed under the GNU GPLv2 and later.
  */

@@ -12,6 +15,7 @@
 #define BCM2836_CONTROL_H

 #include "hw/sysbus.h"
+#include "qemu/timer.h"

 /* 4 mailboxes per core, for 16 total */
 #define BCM2836_NCORES 4
@@ -39,6 +43,12 @@ typedef struct BCM2836ControlState {
     bool gpu_irq, gpu_fiq;
     uint8_t timerirqs[BCM2836_NCORES];

+    /* local timer */
+    uint8_t route_localtimer;
+    uint32_t period;
+    bool triggered;
+    QEMUTimer *timer;
+
     /* interrupt source registers, post-routing (also input-derived;
visible) */
     uint32_t irqsrc[BCM2836_NCORES];
     uint32_t fiqsrc[BCM2836_NCORES];