hw/intc/grlib_irqmp: implements the multiprocessor status register

This implements the multiprocessor status register in grlib-irqmp and
bind it to a start signal, which will be later wired in leon3-generic
to start a cpu.

The EIRQ and BA bits are not implemented.

Based on https://gaisler.com/doc/gr712rc-usermanual.pdf, §8.3.5.

Co-developed-by: Frederic Konrad <konrad.frederic@yahoo.fr>
Signed-off-by: Clément Chigot <chigot@adacore.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240131085047.18458-4-chigot@adacore.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/intc/grlib_irqmp.c

@@ -52,6 +52,10 @@
 #define FORCE_OFFSET     0x80
 #define EXTENDED_OFFSET  0xC0
 
+/* Multiprocessor Status Register  */
+#define MP_STATUS_CPU_STATUS_MASK ((1 << IRQMP_MAX_CPU)-2)
+#define MP_STATUS_NCPU_SHIFT      28
+
 #define MAX_PILS 16
 
 OBJECT_DECLARE_SIMPLE_TYPE(IRQMP, GRLIB_IRQMP)
@@ -65,6 +69,7 @@ struct IRQMP {
 
     unsigned int ncpus;
     IRQMPState *state;
+    qemu_irq start_signal[IRQMP_MAX_CPU];
     qemu_irq irq;
 };
 
@@ -72,6 +77,7 @@ struct IRQMPState {
     uint32_t level;
     uint32_t pending;
     uint32_t clear;
+    uint32_t mpstatus;
     uint32_t broadcast;
 
     uint32_t mask[IRQMP_MAX_CPU];
@@ -182,10 +188,12 @@ static uint64_t grlib_irqmp_read(void *opaque, hwaddr addr,
         return state->force[0];
 
     case CLEAR_OFFSET:
-    case MP_STATUS_OFFSET:
         /* Always read as 0 */
         return 0;
 
+    case MP_STATUS_OFFSET:
+        return state->mpstatus;
+
     case BROADCAST_OFFSET:
         return state->broadcast;
 
@@ -224,8 +232,9 @@ static uint64_t grlib_irqmp_read(void *opaque, hwaddr addr,
 static void grlib_irqmp_write(void *opaque, hwaddr addr,
                               uint64_t value, unsigned size)
 {
-    IRQMP      *irqmp = opaque;
+    IRQMP *irqmp = opaque;
     IRQMPState *state;
+    int i;
 
     assert(irqmp != NULL);
     state = irqmp->state;
@@ -258,7 +267,18 @@ static void grlib_irqmp_write(void *opaque, hwaddr addr,
         return;
 
     case MP_STATUS_OFFSET:
-        /* Read Only (no SMP support) */
+        /*
+         * Writing and reading operations are reversed for the CPU status.
+         * Writing "1" will start the CPU, but reading "1" means that the CPU
+         * is power-down.
+         */
+        value &= MP_STATUS_CPU_STATUS_MASK;
+        for (i = 0; i < irqmp->ncpus; i++) {
+            if ((value >> i) & 1) {
+                qemu_set_irq(irqmp->start_signal[i], 1);
+                state->mpstatus &= ~(1 << i);
+            }
+        }
         return;
 
     case BROADCAST_OFFSET:
@@ -325,6 +345,8 @@ static void grlib_irqmp_reset(DeviceState *d)
 
     memset(irqmp->state, 0, sizeof *irqmp->state);
     irqmp->state->parent = irqmp;
+    irqmp->state->mpstatus = ((irqmp->ncpus - 1) << MP_STATUS_NCPU_SHIFT) |
+        ((1 << irqmp->ncpus) - 2);
 }
 
 static void grlib_irqmp_realize(DeviceState *dev, Error **errp)
@@ -338,6 +360,13 @@ static void grlib_irqmp_realize(DeviceState *dev, Error **errp)
     }
 
     qdev_init_gpio_in(dev, grlib_irqmp_set_irq, MAX_PILS);
+
+    /*
+     * Transitionning from 0 to 1 starts the CPUs. The opposite can't
+     * happen.
+     */
+    qdev_init_gpio_out_named(dev, irqmp->start_signal, "grlib-start-cpu",
+                             IRQMP_MAX_CPU);
     qdev_init_gpio_out_named(dev, &irqmp->irq, "grlib-irq", 1);
     memory_region_init_io(&irqmp->iomem, OBJECT(dev), &grlib_irqmp_ops, irqmp,
                           "irqmp", IRQMP_REG_SIZE);