hw/misc: add a toy i2c echo device

Add an example I2C device to demonstrate how a slave may master the bus
and send data asynchronously to another slave.

The device will echo whatever it is sent to the device identified by the
first byte received.

Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
[ clg: integrated fixes :
  https://lore.kernel.org/qemu-devel/Y3yMKAhOkYGtnkOp@cormorant.local/ ]
Message-Id: <20220601210831.67259-7-its@irrelevant.dk>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

hw/misc/i2c-echo.c

@@ -0,0 +1,156 @@
+#include "qemu/osdep.h"
+#include "qemu/timer.h"
+#include "qemu/main-loop.h"
+#include "block/aio.h"
+#include "hw/i2c/i2c.h"
+
+#define TYPE_I2C_ECHO "i2c-echo"
+OBJECT_DECLARE_SIMPLE_TYPE(I2CEchoState, I2C_ECHO)
+
+enum i2c_echo_state {
+    I2C_ECHO_STATE_IDLE,
+    I2C_ECHO_STATE_START_SEND,
+    I2C_ECHO_STATE_ACK,
+};
+
+typedef struct I2CEchoState {
+    I2CSlave parent_obj;
+
+    I2CBus *bus;
+
+    enum i2c_echo_state state;
+    QEMUBH *bh;
+
+    unsigned int pos;
+    uint8_t data[3];
+} I2CEchoState;
+
+static void i2c_echo_bh(void *opaque)
+{
+    I2CEchoState *state = opaque;
+
+    switch (state->state) {
+    case I2C_ECHO_STATE_IDLE:
+        return;
+
+    case I2C_ECHO_STATE_START_SEND:
+        if (i2c_start_send_async(state->bus, state->data[0])) {
+            goto release_bus;
+        }
+
+        state->pos++;
+        state->state = I2C_ECHO_STATE_ACK;
+        return;
+
+    case I2C_ECHO_STATE_ACK:
+        if (state->pos > 2) {
+            break;
+        }
+
+        if (i2c_send_async(state->bus, state->data[state->pos++])) {
+            break;
+        }
+
+        return;
+    }
+
+
+    i2c_end_transfer(state->bus);
+release_bus:
+    i2c_bus_release(state->bus);
+
+    state->state = I2C_ECHO_STATE_IDLE;
+}
+
+static int i2c_echo_event(I2CSlave *s, enum i2c_event event)
+{
+    I2CEchoState *state = I2C_ECHO(s);
+
+    switch (event) {
+    case I2C_START_RECV:
+        state->pos = 0;
+
+        break;
+
+    case I2C_START_SEND:
+        state->pos = 0;
+
+        break;
+
+    case I2C_FINISH:
+        state->pos = 0;
+        state->state = I2C_ECHO_STATE_START_SEND;
+        i2c_bus_master(state->bus, state->bh);
+
+        break;
+
+    case I2C_NACK:
+        break;
+
+    default:
+        return -1;
+    }
+
+    return 0;
+}
+
+static uint8_t i2c_echo_recv(I2CSlave *s)
+{
+    I2CEchoState *state = I2C_ECHO(s);
+
+    if (state->pos > 2) {
+        return 0xff;
+    }
+
+    return state->data[state->pos++];
+}
+
+static int i2c_echo_send(I2CSlave *s, uint8_t data)
+{
+    I2CEchoState *state = I2C_ECHO(s);
+
+    if (state->pos > 2) {
+        return -1;
+    }
+
+    state->data[state->pos++] = data;
+
+    return 0;
+}
+
+static void i2c_echo_realize(DeviceState *dev, Error **errp)
+{
+    I2CEchoState *state = I2C_ECHO(dev);
+    BusState *bus = qdev_get_parent_bus(dev);
+
+    state->bus = I2C_BUS(bus);
+    state->bh = qemu_bh_new(i2c_echo_bh, state);
+
+    return;
+}
+
+static void i2c_echo_class_init(ObjectClass *oc, void *data)
+{
+    I2CSlaveClass *sc = I2C_SLAVE_CLASS(oc);
+    DeviceClass *dc = DEVICE_CLASS(oc);
+
+    dc->realize = i2c_echo_realize;
+
+    sc->event = i2c_echo_event;
+    sc->recv = i2c_echo_recv;
+    sc->send = i2c_echo_send;
+}
+
+static const TypeInfo i2c_echo = {
+    .name = TYPE_I2C_ECHO,
+    .parent = TYPE_I2C_SLAVE,
+    .instance_size = sizeof(I2CEchoState),
+    .class_init = i2c_echo_class_init,
+};
+
+static void register_types(void)
+{
+    type_register_static(&i2c_echo);
+}
+
+type_init(register_types);

hw/misc/meson.build

@@ -128,6 +128,8 @@ softmmu_ss.add(when: 'CONFIG_NRF51_SOC', if_true: files('nrf51_rng.c'))
 
 softmmu_ss.add(when: 'CONFIG_GRLIB', if_true: files('grlib_ahb_apb_pnp.c'))
 
+softmmu_ss.add(when: 'CONFIG_I2C', if_true: files('i2c-echo.c'))
+
 specific_ss.add(when: 'CONFIG_AVR_POWER', if_true: files('avr_power.c'))
 
 specific_ss.add(when: 'CONFIG_MAC_VIA', if_true: files('mac_via.c'))