hw/gpio/nrf51: implement DETECT signal

Implement nRF51 DETECT signal in the GPIO peripheral.

The reference manual makes mention of a per-pin DETECT signal, but these
are not exposed to the user. See https://devzone.nordicsemi.com/f/nordic-q-a/39858/gpio-per-pin-detect-signal-available
for more information. Currently, I don't see a reason to model these.

Signed-off-by: Chris Laplante <chris@laplante.io>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20230728160324.1159090-2-chris@laplante.io
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/gpio/nrf51_gpio.c

@@ -78,6 +78,7 @@ static void update_state(NRF51GPIOState *s)
     int pull;
     size_t i;
     bool connected_out, dir, connected_in, out, in, input;
+    bool assert_detect = false;
 
     for (i = 0; i < NRF51_GPIO_PINS; i++) {
         pull = pull_value(s->cnf[i]);
@@ -99,7 +100,15 @@ static void update_state(NRF51GPIOState *s)
                 qemu_log_mask(LOG_GUEST_ERROR,
                               "GPIO pin %zu short circuited\n", i);
             }
-            if (!connected_in) {
+            if (connected_in) {
+                uint32_t detect_config = extract32(s->cnf[i], 16, 2);
+                if ((detect_config == 2) && (in == 1)) {
+                    assert_detect = true;
+                }
+                if ((detect_config == 3) && (in == 0)) {
+                    assert_detect = true;
+                }
+            } else {
                 /*
                  * Floating input: the output stimulates IN if connected,
                  * otherwise pull-up/pull-down resistors put a value on both
@@ -116,6 +125,8 @@ static void update_state(NRF51GPIOState *s)
         }
         update_output_irq(s, i, connected_out, out);
     }
+
+    qemu_set_irq(s->detect, assert_detect);
 }
 
 /*
@@ -291,6 +302,7 @@ static void nrf51_gpio_init(Object *obj)
 
     qdev_init_gpio_in(DEVICE(s), nrf51_gpio_set, NRF51_GPIO_PINS);
     qdev_init_gpio_out(DEVICE(s), s->output, NRF51_GPIO_PINS);
+    qdev_init_gpio_out_named(DEVICE(s), &s->detect, "detect", 1);
 }
 
 static void nrf51_gpio_class_init(ObjectClass *klass, void *data)

include/hw/gpio/nrf51_gpio.h

@@ -64,6 +64,7 @@ struct NRF51GPIOState {
     uint32_t old_out_connected;
 
     qemu_irq output[NRF51_GPIO_PINS];
+    qemu_irq detect;
 };