hw/9118.c: Implement active-low interrupt support

The 9118 ethernet controller interrupt line is active low unless
the IRQ config register is programmed to set both the IRQ_POL
(polarity: active-high) and IRQ_TYPE (type: push-pull) bits:
implement support for inverting the irq output in other configurations.
This also requires that we support setting the bits in the first
place, and that we correctly preserve them across software reset.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andrzej Zaborowski <andrew.zaborowski@intel.com>

hw/lan9118.c

@@ -228,6 +228,12 @@ static void lan9118_update(lan9118_state *s)
     if ((s->irq_cfg & IRQ_EN) == 0) {
         level = 0;
     }
+    if ((s->irq_cfg & (IRQ_TYPE | IRQ_POL)) != (IRQ_TYPE | IRQ_POL)) {
+        /* Interrupt is active low unless we're configured as
+         * active-high polarity, push-pull type.
+         */
+        level = !level;
+    }
     qemu_set_irq(s->irq, level);
 }
 
@@ -294,8 +300,7 @@ static void phy_reset(lan9118_state *s)
 static void lan9118_reset(DeviceState *d)
 {
     lan9118_state *s = FROM_SYSBUS(lan9118_state, sysbus_from_qdev(d));
-
-    s->irq_cfg &= ~(IRQ_TYPE | IRQ_POL);
+    s->irq_cfg &= (IRQ_TYPE | IRQ_POL);
     s->int_sts = 0;
     s->int_en = 0;
     s->fifo_int = 0x48000000;
@@ -904,7 +909,8 @@ static void lan9118_writel(void *opaque, target_phys_addr_t offset,
     switch (offset) {
     case CSR_IRQ_CFG:
         /* TODO: Implement interrupt deassertion intervals.  */
-        s->irq_cfg = (s->irq_cfg & IRQ_INT) | (val & IRQ_EN);
+        val &= (IRQ_EN | IRQ_POL | IRQ_TYPE);
+        s->irq_cfg = (s->irq_cfg & IRQ_INT) | val;
         break;
     case CSR_INT_STS:
         s->int_sts &= ~val;