Add a simple i2c peripheral to be used for testing I2C device
models. The peripheral has a fixed number of registers that can be
read and written.

Signed-off-by: Octavian Purdila <tavip@google.com>
---
 tests/unit/i2c_tester.c | 111 ++++++++++++++++++++++++++++++++++++++++
 tests/unit/i2c_tester.h |  34 ++++++++++++
 2 files changed, 145 insertions(+)
 create mode 100644 tests/unit/i2c_tester.c
 create mode 100644 tests/unit/i2c_tester.h

diff --git a/tests/unit/i2c_tester.c b/tests/unit/i2c_tester.c
new file mode 100644
index 0000000000..ea36a17f1f
--- /dev/null
+++ b/tests/unit/i2c_tester.c
@@ -0,0 +1,111 @@
+/*
+ * Simple I2C peripheral for testing I2C device models.
+ *
+ * Copyright (c) 2024 Google LLC
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "i2c_tester.h"
+#include "qemu/log.h"
+#include "qemu/module.h"
+
+static void i2c_tester_reset(DeviceState *ds)
+{
+    I2cTesterState *s = I2C_TESTER(ds);
+
+    s->set_reg_idx = false;
+    s->reg_idx     = 0;
+    memset(s->regs, 0, I2C_TESTER_NUM_REGS);
+}
+
+static int i2c_tester_event(I2CSlave *i2c, enum i2c_event event)
+{
+    I2cTesterState *s = I2C_TESTER(i2c);
+
+    if (event == I2C_START_SEND) {
+        s->set_reg_idx = true;
+    }
+
+    return 0;
+}
+
+static uint8_t i2c_tester_rx(I2CSlave *i2c)
+{
+    I2cTesterState *s = I2C_TESTER(i2c);
+
+    if (s->reg_idx >= I2C_TESTER_NUM_REGS) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: invalid reg 0x%02x\n", __func__,
+                      s->reg_idx);
+        return I2C_NACK;
+    }
+
+    return s->regs[s->reg_idx];
+}
+
+static int i2c_tester_tx(I2CSlave *i2c, uint8_t data)
+{
+    I2cTesterState *s = I2C_TESTER(i2c);
+
+    if (s->set_reg_idx) {
+        /* Setting the register in which the operation will be done. */
+        s->reg_idx = data;
+        s->set_reg_idx = false;
+        return 0;
+    }
+
+    if (s->reg_idx >= I2C_TESTER_NUM_REGS) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: invalid reg 0x%02x\n", __func__,
+                      s->reg_idx);
+        return I2C_NACK;
+    }
+
+    /* Write reg data. */
+    s->regs[s->reg_idx] = data;
+
+    return 0;
+}
+
+static void i2c_tester_init(Object *obj)
+{
+}
+
+static void i2c_tester_realize(DeviceState *ds, Error **errp)
+{
+}
+
+static void i2c_tester_unrealize(DeviceState *dev)
+{
+}
+
+static void i2c_tester_class_init(ObjectClass *oc, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(oc);
+    I2CSlaveClass *isc = I2C_SLAVE_CLASS(oc);
+
+    dc->reset = i2c_tester_reset;
+    dc->realize   = i2c_tester_realize;
+    dc->unrealize = i2c_tester_unrealize;
+
+    isc->event = i2c_tester_event;
+    isc->recv = i2c_tester_rx;
+    isc->send = i2c_tester_tx;
+}
+
+static const TypeInfo i2c_tester_info = {
+    .name = TYPE_I2C_TESTER,
+    .parent = TYPE_I2C_SLAVE,
+    .instance_size = sizeof(I2cTesterState),
+    .instance_init = i2c_tester_init,
+    .class_init = i2c_tester_class_init
+};
+
+static void i2c_tester_register_type(void)
+{
+    type_register_static(&i2c_tester_info);
+}
+
+type_init(i2c_tester_register_type);
diff --git a/tests/unit/i2c_tester.h b/tests/unit/i2c_tester.h
new file mode 100644
index 0000000000..9eebe1b6e3
--- /dev/null
+++ b/tests/unit/i2c_tester.h
@@ -0,0 +1,34 @@
+/*
+ *
+ * Copyright (c) 2024 Google LLC
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef TESTS_UNIT_I2C_TESTER_H
+#define TESTS_UNIT_I2C_TESTER_H
+
+#include "qemu/osdep.h"
+#include "hw/i2c/i2c.h"
+#include "hw/irq.h"
+
+#define I2C_TESTER_NUM_REGS    0x31
+
+#define TYPE_I2C_TESTER "i2c_tester"
+#define I2C_TESTER(obj) OBJECT_CHECK(I2cTesterState, (obj), TYPE_I2C_TESTER)
+
+typedef struct {
+    /* <private> */
+    I2CSlave i2c;
+
+    /* <public> */
+    bool set_reg_idx;
+
+    uint8_t reg_idx;
+    uint8_t regs[I2C_TESTER_NUM_REGS];
+} I2cTesterState;
+
+#endif /* TESTS_UNIT_I2C_TESTER_H */
-- 
2.46.0.rc2.264.g509ed76dc8-goog