2 files changed, 12 insertions, 2 deletions

diff --git a/Documentation/i2c/i2c-stub b/Documentation/i2c/i2c-stub
index d9c383b30925..326d1ee81e0e 100644
--- a/Documentation/i2c/i2c-stub
+++ b/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
diff --git a/drivers/i2c/busses/i2c-stub.c b/drivers/i2c/busses/i2c-stub.c
index 52ebeda1a64b..0c770eabe85e 100644
--- a/drivers/i2c/busses/i2c-stub.c
+++ b/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 = {