misc/pca9552: Let external devices set pca9552 inputs

Allow external devices to drive pca9552 input pins by adding
input GPIO's to the model.  This allows a device to connect
its output GPIO's to the pca9552 input GPIO's.

In order for an external device to set the state of a pca9552
pin, the pin must first be configured for high impedance (LED
is off).  If the pca9552 pin is configured to drive the pin low
(LED is on), then external input will be ignored.

Here is a table describing the logical state of a pca9552 pin
given the state being driven by the pca9552 and an external device:

                   PCA9552
                   Configured
                   State

                  | Hi-Z | Low |
            ------+------+-----+
  External   Hi-Z |  Hi  | Low |
  Device    ------+------+-----+
  State      Low  |  Low | Low |
            ------+------+-----+

Reviewed-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Signed-off-by: Glenn Miles <milesg@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

hw/misc/pca9552.c

@@ -44,6 +44,8 @@ DECLARE_CLASS_CHECKERS(PCA955xClass, PCA955X,
 #define PCA9552_LED_OFF  0x1
 #define PCA9552_LED_PWM0 0x2
 #define PCA9552_LED_PWM1 0x3
+#define PCA9552_PIN_LOW  0x0
+#define PCA9552_PIN_HIZ  0x1
 
 static const char *led_state[] = {"on", "off", "pwm0", "pwm1"};
 
@@ -110,22 +112,27 @@ static void pca955x_update_pin_input(PCA955xState *s)
 
     for (i = 0; i < k->pin_count; i++) {
         uint8_t input_reg = PCA9552_INPUT0 + (i / 8);
-        uint8_t input_shift = (i % 8);
+        uint8_t bit_mask = 1 << (i % 8);
         uint8_t config = pca955x_pin_get_config(s, i);
+        uint8_t old_value = s->regs[input_reg] & bit_mask;
+        uint8_t new_value;
 
         switch (config) {
         case PCA9552_LED_ON:
             /* Pin is set to 0V to turn on LED */
-            qemu_set_irq(s->gpio[i], 0);
+            s->regs[input_reg] &= ~bit_mask;
-            s->regs[input_reg] &= ~(1 << input_shift);
             break;
         case PCA9552_LED_OFF:
             /*
              * Pin is set to Hi-Z to turn off LED and
-             * pullup sets it to a logical 1.
+             * pullup sets it to a logical 1 unless
+             * external device drives it low.
              */
-            qemu_set_irq(s->gpio[i], 1);
+            if (s->ext_state[i] == PCA9552_PIN_LOW) {
-            s->regs[input_reg] |= 1 << input_shift;
+                s->regs[input_reg] &= ~bit_mask;
+            } else {
+                s->regs[input_reg] |=  bit_mask;
+            }
             break;
         case PCA9552_LED_PWM0:
         case PCA9552_LED_PWM1:
@@ -133,6 +140,12 @@ static void pca955x_update_pin_input(PCA955xState *s)
         default:
             break;
         }
+
+        /* update irq state only if pin state changed */
+        new_value = s->regs[input_reg] & bit_mask;
+        if (new_value != old_value) {
+            qemu_set_irq(s->gpio_out[i], !!new_value);
+        }
     }
 }
 
@@ -340,6 +353,7 @@ static const VMStateDescription pca9552_vmstate = {
         VMSTATE_UINT8(len, PCA955xState),
         VMSTATE_UINT8(pointer, PCA955xState),
         VMSTATE_UINT8_ARRAY(regs, PCA955xState, PCA955X_NR_REGS),
+        VMSTATE_UINT8_ARRAY(ext_state, PCA955xState, PCA955X_PIN_COUNT_MAX),
         VMSTATE_I2C_SLAVE(i2c, PCA955xState),
         VMSTATE_END_OF_LIST()
     }
@@ -358,6 +372,7 @@ static void pca9552_reset(DeviceState *dev)
     s->regs[PCA9552_LS2] = 0x55;
     s->regs[PCA9552_LS3] = 0x55;
 
+    memset(s->ext_state, PCA9552_PIN_HIZ, PCA955X_PIN_COUNT_MAX);
     pca955x_update_pin_input(s);
 
     s->pointer = 0xFF;
@@ -380,6 +395,26 @@ static void pca955x_initfn(Object *obj)
     }
 }
 
+static void pca955x_set_ext_state(PCA955xState *s, int pin, int level)
+{
+    if (s->ext_state[pin] != level) {
+        uint16_t pins_status = pca955x_pins_get_status(s);
+        s->ext_state[pin] = level;
+        pca955x_update_pin_input(s);
+        pca955x_display_pins_status(s, pins_status);
+    }
+}
+
+static void pca955x_gpio_in_handler(void *opaque, int pin, int level)
+{
+
+    PCA955xState *s = PCA955X(opaque);
+    PCA955xClass *k = PCA955X_GET_CLASS(s);
+
+    assert((pin >= 0) && (pin < k->pin_count));
+    pca955x_set_ext_state(s, pin, level);
+}
+
 static void pca955x_realize(DeviceState *dev, Error **errp)
 {
     PCA955xClass *k = PCA955X_GET_CLASS(dev);
@@ -389,7 +424,8 @@ static void pca955x_realize(DeviceState *dev, Error **errp)
         s->description = g_strdup("pca-unspecified");
     }
 
-    qdev_init_gpio_out(dev, s->gpio, k->pin_count);
+    qdev_init_gpio_out(dev, s->gpio_out, k->pin_count);
+    qdev_init_gpio_in(dev, pca955x_gpio_in_handler, k->pin_count);
 }
 
 static Property pca955x_properties[] = {

include/hw/misc/pca9552.h

@@ -30,7 +30,8 @@ struct PCA955xState {
     uint8_t pointer;
 
     uint8_t regs[PCA955X_NR_REGS];
-    qemu_irq gpio[PCA955X_PIN_COUNT_MAX];
+    qemu_irq gpio_out[PCA955X_PIN_COUNT_MAX];
+    uint8_t ext_state[PCA955X_PIN_COUNT_MAX];
     char *description; /* For debugging purpose only */
 };