diff options
2 files changed, 31 insertions, 3 deletions
diff --git a/Documentation/i2c/i2c-stub b/Documentation/i2c/i2c-stub
index d6dcb138abf5..9cc081e69764 100644
--- a/Documentation/i2c/i2c-stub
+++ b/Documentation/i2c/i2c-stub
@@ -6,9 +6,12 @@ This module is a very simple fake I2C/SMBus driver. It implements four
types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, and
(r/w) word data.
+You need to provide a chip address as a module parameter when loading
+this driver, which will then only react to SMBus commands to this address.
No hardware is needed nor associated with this module. It will accept write
-quick commands to all addresses; it will respond to the other commands (also
-to all addresses) by reading from or writing to an array in memory. It will
+quick commands to one address; it will respond to the other commands (also
+to one address) by reading from or writing to an array in memory. It will
also spam the kernel logs for every command it handles.
A pointer register with auto-increment is implemented for all byte
@@ -21,6 +24,11 @@ The typical use-case is like this:
3. load the target sensors chip driver module
4. observe its behavior in the kernel log
+int chip_addr:
+ The SMBus address to emulate a chip at.
There are independent arrays for byte/data and word/data commands. Depending
@@ -33,6 +41,9 @@ If the hardware for your driver has banked registers (e.g. Winbond sensors
chips) this module will not work well - although it could be extended to
support that pretty easily.
+Only one chip address is supported - although this module could be
+extended to support more.
If you spam it hard enough, printk can be lossy. This module really wants
something like relayfs.
diff --git a/drivers/i2c/busses/i2c-stub.c b/drivers/i2c/busses/i2c-stub.c
index 73f481e93a36..8cf374ddd989 100644
--- a/drivers/i2c/busses/i2c-stub.c
+++ b/drivers/i2c/busses/i2c-stub.c
@@ -27,6 +27,10 @@
#include <linux/errno.h>
#include <linux/i2c.h>
+static unsigned short chip_addr;
+module_param(chip_addr, ushort, S_IRUGO);
+MODULE_PARM_DESC(chip_addr, "Chip address (between 0x03 and 0x77)\n");
static u8 stub_pointer;
static u8 stub_bytes[256];
static u16 stub_words[256];
@@ -37,6 +41,9 @@ static s32 stub_xfer(struct i2c_adapter * adap, u16 addr, unsigned short flags,
s32 ret;
+ if (addr != chip_addr)
+ return -ENODEV;
switch (size) {
@@ -122,7 +129,17 @@ static struct i2c_adapter stub_adapter = {
static int __init i2c_stub_init(void)
- printk(KERN_INFO "i2c-stub loaded\n");
+ if (!chip_addr) {
+ printk(KERN_ERR "i2c-stub: Please specify a chip address\n");
+ return -ENODEV;
+ }
+ if (chip_addr < 0x03 || chip_addr > 0x77) {
+ printk(KERN_ERR "i2c-stub: Invalid chip address 0x%02x\n",
+ chip_addr);
+ return -EINVAL;
+ }
+ printk(KERN_INFO "i2c-stub: Virtual chip at 0x%02x\n", chip_addr);
return i2c_add_adapter(&stub_adapter);