i2c: gpio: fault-injector: add incomplete_write_byte

Add another injector for an incomplete transfer. As mentioned in the
docs, this one is important to check bus recovery algorithms with it.
Otherwise random data may be sent to devices!
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Documentation/i2c/gpio-fault-injection

@@ -60,3 +60,22 @@ above, the bus master under test should detect this condition and try a bus
 recovery. This time, however, it should succeed and the device should release
 SDA after toggling SCL.
 
+"incomplete_write_byte"
+-----------------------
+
+Similar to above, this file is write only and you need to write the address of
+an existing I2C client device to it.
+
+The injector will again stop at one ACK phase, so the device will keep SDA low
+because it acknowledges data. However, there are two differences compared to
+'incomplete_address_phase':
+
+a) the message sent out will be a write message
+b) after the address byte, a 0x00 byte will be transferred. Then, stop at ACK.
+
+This is a highly delicate state, the device is set up to write any data to
+register 0x00 (if it has registers) when further clock pulses happen on SCL.
+This is why bus recovery (up to 9 clock pulses) must either check SDA or send
+additional STOP conditions to ensure the bus has been released. Otherwise
+random data will be written to a device!
+

drivers/i2c/busses/i2c-gpio.c

@@ -143,6 +143,25 @@ static int fops_incomplete_addr_phase_set(void *data, u64 addr)
 }
 DEFINE_DEBUGFS_ATTRIBUTE(fops_incomplete_addr_phase, NULL, fops_incomplete_addr_phase_set, "%llu\n");
 
+static int fops_incomplete_write_byte_set(void *data, u64 addr)
+{
+	struct i2c_gpio_private_data *priv = data;
+	u32 pattern;
+
+	if (addr > 0x7f)
+		return -EINVAL;
+
+	/* ADDR (7 bit) + WR (1 bit) + Client ACK (1 bit) */
+	pattern = (addr << 2) | 1;
+	/* 0x00 (8 bit) + Client ACK, keep SDA hi (1 bit) */
+	pattern = (pattern << 9) | 1;
+
+	i2c_gpio_incomplete_transfer(priv, pattern, 18);
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(fops_incomplete_write_byte, NULL, fops_incomplete_write_byte_set, "%llu\n");
+
 static void i2c_gpio_fault_injector_init(struct platform_device *pdev)
 {
 	struct i2c_gpio_private_data *priv = platform_get_drvdata(pdev);
@@ -166,6 +185,8 @@ static void i2c_gpio_fault_injector_init(struct platform_device *pdev)
 	debugfs_create_file_unsafe("sda", 0600, priv->debug_dir, priv, &fops_sda);
 	debugfs_create_file_unsafe("incomplete_address_phase", 0200, priv->debug_dir,
 				   priv, &fops_incomplete_addr_phase);
+	debugfs_create_file_unsafe("incomplete_write_byte", 0200, priv->debug_dir,
+				   priv, &fops_incomplete_write_byte);
 }
 
 static void i2c_gpio_fault_injector_exit(struct platform_device *pdev)