hw/misc/led: Allow connecting from GPIO output

Some devices expose GPIO lines.

Add a GPIO qdev input to our LED device, so we can
connect a GPIO output using qdev_connect_gpio_out().

When used with GPIOs, the intensity can only be either
minium or maximum. This depends of the polarity of the
GPIO (which can be inverted).
Declare the GpioPolarity type to model the polarity.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Message-Id: <20200912134041.946260-3-f4bug@amsat.org>

hw/misc/led.c

@@ -10,6 +10,7 @@
 #include "migration/vmstate.h"
 #include "hw/qdev-properties.h"
 #include "hw/misc/led.h"
+#include "hw/irq.h"
 #include "trace.h"
 
 #define LED_INTENSITY_PERCENT_MAX   100
@@ -53,11 +54,19 @@ void led_set_state(LEDState *s, bool is_emitting)
     led_set_intensity(s, is_emitting ? LED_INTENSITY_PERCENT_MAX : 0);
 }
 
+static void led_set_state_gpio_handler(void *opaque, int line, int new_state)
+{
+    LEDState *s = LED(opaque);
+
+    assert(line == 0);
+    led_set_state(s, !!new_state != s->gpio_active_high);
+}
+
 static void led_reset(DeviceState *dev)
 {
     LEDState *s = LED(dev);
 
-    led_set_state(s, false);
+    led_set_state(s, s->gpio_active_high);
 }
 
 static const VMStateDescription vmstate_led = {
@@ -84,11 +93,14 @@ static void led_realize(DeviceState *dev, Error **errp)
     if (s->description == NULL) {
         s->description = g_strdup("n/a");
     }
+
+    qdev_init_gpio_in(DEVICE(s), led_set_state_gpio_handler, 1);
 }
 
 static Property led_properties[] = {
     DEFINE_PROP_STRING("color", LEDState, color),
     DEFINE_PROP_STRING("description", LEDState, description),
+    DEFINE_PROP_BOOL("gpio-active-high", LEDState, gpio_active_high, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -119,6 +131,7 @@ static void led_register_types(void)
 type_init(led_register_types)
 
 LEDState *led_create_simple(Object *parentobj,
+                            GpioPolarity gpio_polarity,
                             LEDColor color,
                             const char *description)
 {
@@ -126,6 +139,8 @@ LEDState *led_create_simple(Object *parentobj,
     DeviceState *dev;
 
     dev = qdev_new(TYPE_LED);
+    qdev_prop_set_bit(dev, "gpio-active-high",
+                      gpio_polarity == GPIO_POLARITY_ACTIVE_HIGH);
     qdev_prop_set_string(dev, "color", led_color_name[color]);
     if (!description) {
         static unsigned undescribed_led_id;

include/hw/misc/led.h

@@ -9,6 +9,7 @@
 #define HW_MISC_LED_H
 
 #include "qom/object.h"
+#include "hw/qdev-core.h"
 
 #define TYPE_LED "led"
 
@@ -37,10 +38,17 @@ struct LEDState {
     /* Public */
 
     uint8_t intensity_percent;
+    qemu_irq irq;
 
     /* Properties */
     char *description;
     char *color;
+    /*
+     * Determines whether a GPIO is using a positive (active-high)
+     * logic (when used with GPIO, the intensity at reset is related
+     * to the GPIO polarity).
+     */
+    bool gpio_active_high;
 };
 typedef struct LEDState LEDState;
 DECLARE_INSTANCE_CHECKER(LEDState, LED, TYPE_LED)
@@ -72,6 +80,7 @@ void led_set_state(LEDState *s, bool is_emitting);
 /**
  * led_create_simple: Create and realize a LED device
  * @parentobj: the parent object
+ * @gpio_polarity: GPIO polarity
  * @color: color of the LED
  * @description: description of the LED (optional)
  *
@@ -81,6 +90,7 @@ void led_set_state(LEDState *s, bool is_emitting);
  * Returns: The newly allocated and instantiated LED object.
  */
 LEDState *led_create_simple(Object *parentobj,
+                            GpioPolarity gpio_polarity,
                             LEDColor color,
                             const char *description);
 

include/hw/qdev-core.h

@@ -443,6 +443,22 @@ void qdev_simple_device_unplug_cb(HotplugHandler *hotplug_dev,
 void qdev_machine_creation_done(void);
 bool qdev_machine_modified(void);
 
+/**
+ * GpioPolarity: Polarity of a GPIO line
+ *
+ * GPIO lines use either positive (active-high) logic,
+ * or negative (active-low) logic.
+ *
+ * In active-high logic (%GPIO_POLARITY_ACTIVE_HIGH), a pin is
+ * active when the voltage on the pin is high (relative to ground);
+ * whereas in active-low logic (%GPIO_POLARITY_ACTIVE_LOW), a pin
+ * is active when the voltage on the pin is low (or grounded).
+ */
+typedef enum {
+    GPIO_POLARITY_ACTIVE_LOW,
+    GPIO_POLARITY_ACTIVE_HIGH
+} GpioPolarity;
+
 /**
  * qdev_get_gpio_in: Get one of a device's anonymous input GPIO lines
  * @dev: Device whose GPIO we want