i2c-stub: Allow user to disable some commands

Add a module parameter to override the functionality bitfield. This
lets the user disable some commands. This can be used to force a chip
driver to take different code paths.
Signed-off-by: Jean Delvare <khali@linux-fr.org>

Documentation/i2c/i2c-stub

@@ -33,6 +33,12 @@ PARAMETERS:
 int chip_addr[10]:
 	The SMBus addresses to emulate chips at.
 
+unsigned long functionality:
+	Functionality override, to disable some commands. See I2C_FUNC_*
+	constants in <linux/i2c.h> for the suitable values. For example,
+	value 0x1f0000 would only enable the quick, byte and byte data
+	commands.
+
 CAVEATS:
 
 If your target driver polls some byte or word waiting for it to change, the

drivers/i2c/busses/i2c-stub.c

@@ -35,6 +35,10 @@ module_param_array(chip_addr, ushort, NULL, S_IRUGO);
 MODULE_PARM_DESC(chip_addr,
 		 "Chip addresses (up to 10, between 0x03 and 0x77)");
 
+static unsigned long functionality = ~0UL;
+module_param(functionality, ulong, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(functionality, "Override functionality bitfield");
+
 struct stub_chip {
 	u8 pointer;
 	u16 words[256];		/* Byte operations use the LSB as per SMBus
@@ -152,9 +156,9 @@ static s32 stub_xfer(struct i2c_adapter * adap, u16 addr, unsigned short flags,
 
 static u32 stub_func(struct i2c_adapter *adapter)
 {
-	return I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE |
+	return (I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE |
 		I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA |
-		I2C_FUNC_SMBUS_I2C_BLOCK;
+		I2C_FUNC_SMBUS_I2C_BLOCK) & functionality;
 }
 
 static const struct i2c_algorithm smbus_algorithm = {