[3/3] i2c: testunit: add SMBusAlert trigger

diff --git a/Documentation/i2c/slave-testunit-backend.rst b/Documentation/i2c/slave-testunit-backend.rst
index 3743188ecfc7..d752f433be07 100644
--- a/Documentation/i2c/slave-testunit-backend.rst
+++ b/Documentation/i2c/slave-testunit-backend.rst
@@ -185,3 +185,51 @@  default response::
 
   # i2cset -y 0 0x30 4 0 0 i; i2cget -y 0 0x30
   0x00
+
+0x05 SMBUS_ALERT_REQUEST
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. list-table::
+  :header-rows: 1
+
+  * - CMD
+    - DATAL
+    - DATAH
+    - DELAY
+
+  * - 0x05
+    - response value (7 MSBs interpreted as I2C address)
+    - currently unused
+    - n * 10ms
+
+This test raises an interrupt via the SMBAlert pin which the host controller
+must handle. The pin must be connected to the testunit as a GPIO. GPIO access
+is not allowed to sleep. Currently, this can only be described using firmware
+nodes. So, for devicetree, you would add something like this to the testunit
+node::
+
+  gpios = <&gpio1 24 GPIO_ACTIVE_LOW>;
+
+The following command will trigger the alert with a response of 0xc9 after 1
+second of delay::
+
+  # i2cset -y 0 0x30 5 0xc9 0x00 100 i
+
+If the host controller supports SMBusAlert, this message with debug level
+should appear::
+
+  smbus_alert 0-000c: SMBALERT# from dev 0x64, flag 1
+
+This message may appear more than once because the testunit is software not
+hardware and, thus, may not be able to react to the response of the host fast
+enough. The interrupt count should increase only by one, though::
+
+  # cat /proc/interrupts | grep smbus_alert
+   93:          1  gpio-rcar  26 Edge      smbus_alert
+
+If the host does not respond to the alert within 1 second, the test will be
+aborted and the testunit will report an error.
+
+For this test, the testunit will shortly drop its assigned address and listen
+on the SMBus Alert Response Address (0x0c). It will reassign its original
+address afterwards.
diff --git a/drivers/i2c/i2c-slave-testunit.c b/drivers/i2c/i2c-slave-testunit.c
index df54185e5e9a..9fe3150378e8 100644
--- a/drivers/i2c/i2c-slave-testunit.c
+++ b/drivers/i2c/i2c-slave-testunit.c
@@ -8,6 +8,8 @@ 
 
 #include <generated/utsrelease.h>
 #include <linux/bitops.h>
+#include <linux/completion.h>
+#include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/init.h>
 #include <linux/module.h>
@@ -22,6 +24,7 @@  enum testunit_cmds {
 	TU_CMD_SMBUS_HOST_NOTIFY,
 	TU_CMD_SMBUS_BLOCK_PROC_CALL,
 	TU_CMD_GET_VERSION_WITH_REP_START,
+	TU_CMD_SMBUS_ALERT_REQUEST,
 	TU_NUM_CMDS
 };
 
@@ -44,10 +47,37 @@  struct testunit_data {
 	u8 read_idx;
 	struct i2c_client *client;
 	struct delayed_work worker;
+	struct gpio_desc *gpio;
+	struct completion alert_done;
 };
 
 static char tu_version_info[] = "v" UTS_RELEASE "\n\0";
 
+static int i2c_slave_testunit_smbalert_cb(struct i2c_client *client,
+					  enum i2c_slave_event event, u8 *val)
+{
+	struct testunit_data *tu = i2c_get_clientdata(client);
+
+	switch (event) {
+	case I2C_SLAVE_READ_PROCESSED:
+		gpiod_set_value(tu->gpio, 0);
+		fallthrough;
+	case I2C_SLAVE_READ_REQUESTED:
+		*val = tu->regs[TU_REG_DATAL];
+		break;
+
+	case I2C_SLAVE_STOP:
+		complete(&tu->alert_done);
+		break;
+
+	case I2C_SLAVE_WRITE_REQUESTED:
+	case I2C_SLAVE_WRITE_RECEIVED:
+		return -EOPNOTSUPP;
+	}
+
+	return 0;
+}
+
 static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 				     enum i2c_slave_event event, u8 *val)
 {
@@ -127,8 +157,10 @@  static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 static void i2c_slave_testunit_work(struct work_struct *work)
 {
 	struct testunit_data *tu = container_of(work, struct testunit_data, worker.work);
+	unsigned long time_left;
 	struct i2c_msg msg;
 	u8 msgbuf[256];
+	u16 orig_addr;
 	int ret = 0;
 
 	msg.addr = I2C_CLIENT_END;
@@ -150,6 +182,26 @@  static void i2c_slave_testunit_work(struct work_struct *work)
 		msgbuf[2] = tu->regs[TU_REG_DATAH];
 		break;
 
+	case TU_CMD_SMBUS_ALERT_REQUEST:
+		i2c_slave_unregister(tu->client);
+		orig_addr = tu->client->addr;
+		tu->client->addr = 0x0c;
+		ret = i2c_slave_register(tu->client, i2c_slave_testunit_smbalert_cb);
+		if (ret)
+			goto out_smbalert;
+
+		reinit_completion(&tu->alert_done);
+		gpiod_set_value(tu->gpio, 1);
+		time_left = wait_for_completion_timeout(&tu->alert_done, HZ);
+		if (!time_left)
+			ret = -ETIMEDOUT;
+
+		i2c_slave_unregister(tu->client);
+out_smbalert:
+		tu->client->addr = orig_addr;
+		i2c_slave_register(tu->client, i2c_slave_testunit_slave_cb);
+		break;
+
 	default:
 		break;
 	}
@@ -176,8 +228,15 @@  static int i2c_slave_testunit_probe(struct i2c_client *client)
 
 	tu->client = client;
 	i2c_set_clientdata(client, tu);
+	init_completion(&tu->alert_done);
 	INIT_DELAYED_WORK(&tu->worker, i2c_slave_testunit_work);
 
+	tu->gpio = devm_gpiod_get_index_optional(&client->dev, NULL, 0, GPIOD_OUT_LOW);
+	if (gpiod_cansleep(tu->gpio)) {
+		dev_err(&client->dev, "GPIO access which may sleep is not allowed\n");
+		return -EDEADLK;
+	}
+
 	if (sizeof(tu_version_info) > TU_VERSION_MAX_LENGTH)
 		tu_version_info[TU_VERSION_MAX_LENGTH - 1] = 0;