Add a simple SPI peripheral that echoes back received data. Useful for
testing SPI controllers.

Signed-off-by: Octavian Purdila <tavip@google.com>
---
 tests/unit/spi_tester.h | 32 +++++++++++++++++++++++
 tests/unit/spi_tester.c | 57 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)
 create mode 100644 tests/unit/spi_tester.h
 create mode 100644 tests/unit/spi_tester.c

diff --git a/tests/unit/spi_tester.h b/tests/unit/spi_tester.h
new file mode 100644
index 0000000000..16e08d2b5c
--- /dev/null
+++ b/tests/unit/spi_tester.h
@@ -0,0 +1,32 @@
+/*
+ * Simple SPI peripheral device used for SPI controller testing.
+ *
+ * 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_SPI_TESTER_H
+#define TESTS_UNIT_SPI_TESTER_H
+
+#include "qemu/osdep.h"
+#include "qemu/log.h"
+#include "qemu/module.h"
+#include "qemu/bswap.h"
+#include "hw/irq.h"
+#include "hw/ssi/ssi.h"
+#include "qemu/timer.h"
+#include "hw/qdev-properties.h"
+
+#define TYPE_SPI_TESTER "spi-tester"
+#define SPI_TESTER(obj) OBJECT_CHECK(SpiTesterState, (obj), TYPE_SPI_TESTER)
+
+typedef struct {
+    SSIPeripheral ssidev;
+    bool cs;
+} SpiTesterState;
+
+#endif /* TESTS_UNIT_SPI_TESTER_H */
diff --git a/tests/unit/spi_tester.c b/tests/unit/spi_tester.c
new file mode 100644
index 0000000000..e055d25990
--- /dev/null
+++ b/tests/unit/spi_tester.c
@@ -0,0 +1,57 @@
+/*
+ * Simple SPI peripheral echo device used for SPI controller testing.
+ *
+ * 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 "spi_tester.h"
+
+static uint32_t spi_tester_transfer(SSIPeripheral *dev, uint32_t value)
+{
+    SpiTesterState *s = SPI_TESTER(dev);
+
+    if (s->cs) {
+        return 0;
+    }
+
+    return value;
+}
+
+static void spi_tester_realize(SSIPeripheral *d, Error **errp)
+{
+}
+
+static int spi_tester_set_cs(SSIPeripheral *dev, bool select)
+{
+    SpiTesterState *s = SPI_TESTER(dev);
+
+    s->cs = select;
+
+    return 0;
+}
+
+static void spi_tester_class_init(ObjectClass *klass, void *data)
+{
+    SSIPeripheralClass *k = SSI_PERIPHERAL_CLASS(klass);
+
+    k->realize     = spi_tester_realize;
+    k->transfer    = spi_tester_transfer;
+    k->set_cs      = spi_tester_set_cs;
+    k->cs_polarity = SSI_CS_LOW;
+}
+
+static const TypeInfo spi_tester_types[] = {
+    {
+        .name          = TYPE_SPI_TESTER,
+        .parent        = TYPE_SSI_PERIPHERAL,
+        .instance_size = sizeof(SpiTesterState),
+        .class_init    = spi_tester_class_init,
+    },
+};
+
+DEFINE_TYPES(spi_tester_types);
-- 
2.46.0.184.g6999bdac58-goog