i2c: testunit: add support for block process calls

Devices offering SMBus block process calls are rare, so add it to the
testunit. This is also a good test case for testing proper
I2C_M_RECV_LEN flag handling of I2C bus masters emulating SMBus.

Signed-off-by: Wolfram Sang <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

Documentation/i2c/slave-testunit-backend.rst

···
 
 After that, you will have a write-only device listening. Reads will just return
 an 8-bit version number of the testunit. When writing, the device consists of 4
-8-bit registers and all must be written to start a testcase, i.e. you must
-always write 4 bytes to the device. The registers are:
+8-bit registers and, except for some "partial" commands, all registers must be
+written to start a testcase, i.e. you usually write 4 bytes to the device. The
+registers are:
 
 0x00 CMD   - which test to trigger
 0x01 DATAL - configuration byte 1 for the test
···
 notification after 10ms:
 
 # i2cset -y 0 0x30 0x02 0x42 0x64 0x01 i
+
+0x03 SMBUS_BLOCK_PROC_CALL (partial command)
+   DATAL - must be '1', i.e. one further byte will be written
+   DATAH - number of bytes to be sent back
+   DELAY - not applicable, partial command!
+
+This test will respond to a block process call as defined by the SMBus
+specification. The one data byte written specifies how many bytes will be sent
+back in the following read transfer. Note that in this read transfer, the
+testunit will prefix the length of the bytes to follow. So, if your host bus
+driver emulates SMBus calls like the majority does, it needs to support the
+I2C_M_RECV_LEN flag of an i2c_msg. This is a good testcase for it. The returned
+data consists of the length first, and then of an array of bytes from length-1
+to 0. Here is an example which emulates i2c_smbus_block_process_call() using
+i2ctransfer (you need i2c-tools v4.2 or later):
+
+# i2ctransfer -y 0 w3@0x30 0x03 0x01 0x10 r?
+0x10 0x0f 0x0e 0x0d 0x0c 0x0b 0x0a 0x09 0x08 0x07 0x06 0x05 0x04 0x03 0x02 0x01 0x00

drivers/i2c/i2c-slave-testunit.c

···
 enum testunit_cmds {
 	TU_CMD_READ_BYTES = 1,	/* save 0 for ABORT, RESET or similar */
 	TU_CMD_HOST_NOTIFY,
+	TU_CMD_SMBUS_BLOCK_PROC_CALL,
 	TU_NUM_CMDS
 };
 
···
 				     enum i2c_slave_event event, u8 *val)
 {
 	struct testunit_data *tu = i2c_get_clientdata(client);
+	bool is_proc_call = tu->reg_idx == 3 && tu->regs[TU_REG_DATAL] == 1 &&
+			    tu->regs[TU_REG_CMD] == TU_CMD_SMBUS_BLOCK_PROC_CALL;
 	int ret = 0;
 
 	switch (event) {
···
 		fallthrough;
 
 	case I2C_SLAVE_WRITE_REQUESTED:
+		memset(tu->regs, 0, TU_NUM_REGS);
 		tu->reg_idx = 0;
 		break;
 
-	case I2C_SLAVE_READ_REQUESTED:
 	case I2C_SLAVE_READ_PROCESSED:
-		*val = TU_CUR_VERSION;
+		if (is_proc_call && tu->regs[TU_REG_DATAH])
+			tu->regs[TU_REG_DATAH]--;
+		fallthrough;
+
+	case I2C_SLAVE_READ_REQUESTED:
+		*val = is_proc_call ? tu->regs[TU_REG_DATAH] : TU_CUR_VERSION;
 		break;
 	}