i2c: add slave testunit driver

Here is an I2C slave backend driver which allows to test some uncommon
functionalities of the I2C and SMBus world. Usually, you need specific
devices to test e.g. SMBus Host Notify and such. With this driver you
just need the slave interface of another I2C controller.

This initial version has testcases for multi-master and SMBus Host
Notify. Already planned but not yet implemented are SMBus Alert and
messages with I2C_M_RECV_LEN.

Please read the documentation for further details.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

1 files changed, 175 insertions, 0 deletions

diff --git a/drivers/i2c/i2c-slave-testunit.c b/drivers/i2c/i2c-slave-testunit.c
new file mode 100644
index 000000000000..c288102de324
--- /dev/null
+++ b/drivers/i2c/i2c-slave-testunit.c
@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * I2C slave mode testunit
+ *
+ * Copyright (C) 2020 by Wolfram Sang, Sang Engineering <wsa@sang-engineering.com>
+ * Copyright (C) 2020 by Renesas Electronics Corporation
+ */
+
+#include <linux/bitops.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h> /* FIXME: is system_long_wq the best choice? */
+
+#define TU_CUR_VERSION 0x01
+
+enum testunit_cmds {
+	TU_CMD_READ_BYTES = 1,	/* save 0 for ABORT, RESET or similar */
+	TU_CMD_HOST_NOTIFY,
+	TU_NUM_CMDS
+};
+
+enum testunit_regs {
+	TU_REG_CMD,
+	TU_REG_DATAL,
+	TU_REG_DATAH,
+	TU_REG_DELAY,
+	TU_NUM_REGS
+};
+
+enum testunit_flags {
+	TU_FLAG_IN_PROCESS,
+};
+
+struct testunit_data {
+	unsigned long flags;
+	u8 regs[TU_NUM_REGS];
+	u8 reg_idx;
+	struct i2c_client *client;
+	struct delayed_work worker;
+};
+
+static void i2c_slave_testunit_work(struct work_struct *work)
+{
+	struct testunit_data *tu = container_of(work, struct testunit_data, worker.work);
+	struct i2c_msg msg;
+	u8 msgbuf[256];
+	int ret = 0;
+
+	msg.addr = I2C_CLIENT_END;
+	msg.buf = msgbuf;
+
+	switch (tu->regs[TU_REG_CMD]) {
+	case TU_CMD_READ_BYTES:
+		msg.addr = tu->regs[TU_REG_DATAL];
+		msg.flags = I2C_M_RD;
+		msg.len = tu->regs[TU_REG_DATAH];
+		break;
+
+	case TU_CMD_HOST_NOTIFY:
+		msg.addr = 0x08;
+		msg.flags = 0;
+		msg.len = 3;
+		msgbuf[0] = tu->client->addr;
+		msgbuf[1] = tu->regs[TU_REG_DATAL];
+		msgbuf[2] = tu->regs[TU_REG_DATAH];
+		break;
+
+	default:
+		break;
+	}
+
+	if (msg.addr != I2C_CLIENT_END) {
+		ret = i2c_transfer(tu->client->adapter, &msg, 1);
+		/* convert '0 msgs transferred' to errno */
+		ret = (ret == 0) ? -EIO : ret;
+	}
+
+	if (ret < 0)
+		dev_err(&tu->client->dev, "CMD%02X failed (%d)\n", tu->regs[TU_REG_CMD], ret);
+
+	clear_bit(TU_FLAG_IN_PROCESS, &tu->flags);
+}
+
+static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
+				     enum i2c_slave_event event, u8 *val)
+{
+	struct testunit_data *tu = i2c_get_clientdata(client);
+	int ret = 0;
+
+	switch (event) {
+	case I2C_SLAVE_WRITE_RECEIVED:
+		if (test_bit(TU_FLAG_IN_PROCESS, &tu->flags))
+			return -EBUSY;
+
+		if (tu->reg_idx < TU_NUM_REGS)
+			tu->regs[tu->reg_idx] = *val;
+		else
+			ret = -EMSGSIZE;
+
+		if (tu->reg_idx <= TU_NUM_REGS)
+			tu->reg_idx++;
+
+		/* TU_REG_CMD always written at this point */
+		if (tu->regs[TU_REG_CMD] >= TU_NUM_CMDS)
+			ret = -EINVAL;
+
+		break;
+
+	case I2C_SLAVE_STOP:
+		if (tu->reg_idx == TU_NUM_REGS) {
+			set_bit(TU_FLAG_IN_PROCESS, &tu->flags);
+			queue_delayed_work(system_long_wq, &tu->worker,
+					   msecs_to_jiffies(10 * tu->regs[TU_REG_DELAY]));
+		}
+		fallthrough;
+
+	case I2C_SLAVE_WRITE_REQUESTED:
+		tu->reg_idx = 0;
+		break;
+
+	case I2C_SLAVE_READ_REQUESTED:
+	case I2C_SLAVE_READ_PROCESSED:
+		*val = TU_CUR_VERSION;
+		break;
+	}
+
+	return ret;
+}
+
+static int i2c_slave_testunit_probe(struct i2c_client *client)
+{
+	struct testunit_data *tu;
+
+	tu = devm_kzalloc(&client->dev, sizeof(struct testunit_data), GFP_KERNEL);
+	if (!tu)
+		return -ENOMEM;
+
+	tu->client = client;
+	i2c_set_clientdata(client, tu);
+	INIT_DELAYED_WORK(&tu->worker, i2c_slave_testunit_work);
+
+	return i2c_slave_register(client, i2c_slave_testunit_slave_cb);
+};
+
+static int i2c_slave_testunit_remove(struct i2c_client *client)
+{
+	struct testunit_data *tu = i2c_get_clientdata(client);
+
+	cancel_delayed_work_sync(&tu->worker);
+	i2c_slave_unregister(client);
+	return 0;
+}
+
+static const struct i2c_device_id i2c_slave_testunit_id[] = {
+	{ "slave-testunit", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, i2c_slave_testunit_id);
+
+static struct i2c_driver i2c_slave_testunit_driver = {
+	.driver = {
+		.name = "i2c-slave-testunit",
+	},
+	.probe_new = i2c_slave_testunit_probe,
+	.remove = i2c_slave_testunit_remove,
+	.id_table = i2c_slave_testunit_id,
+};
+module_i2c_driver(i2c_slave_testunit_driver);
+
+MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
+MODULE_DESCRIPTION("I2C slave mode test unit");
+MODULE_LICENSE("GPL v2");