The description of the delay parameter is incomplete, it suggests that there is a direct relation between the delay value and the bus frequency. In fact, due to additional delays in the i2c bitbanging code, the i2c clock is always much slower. Signed-off-by: Jean Delvare <khali@xxxxxxxxxxxx> Cc: Till Harbaum <Till@xxxxxxxxxxx> --- drivers/i2c/busses/i2c-tiny-usb.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- linux-2.6.33-rc6.orig/drivers/i2c/busses/i2c-tiny-usb.c 2010-02-05 18:34:53.000000000 +0100 +++ linux-2.6.33-rc6/drivers/i2c/busses/i2c-tiny-usb.c 2010-02-05 18:39:59.000000000 +0100 @@ -31,11 +31,13 @@ #define CMD_I2C_IO_BEGIN (1<<0) #define CMD_I2C_IO_END (1<<1) -/* i2c bit delay, default is 10us -> 100kHz */ +/* i2c bit delay, default is 10us -> 100kHz max + (in practice, due to additional delays in the i2c bitbanging + code this results in a i2c clock of about 50kHz) */ static unsigned short delay = 10; module_param(delay, ushort, 0); -MODULE_PARM_DESC(delay, "bit delay in microseconds, " - "e.g. 10 for 100kHz (default is 100kHz)"); +MODULE_PARM_DESC(delay, "bit delay in microseconds " + "(default is 10us for 100kHz max)"); static int usb_read(struct i2c_adapter *adapter, int cmd, int value, int index, void *data, int len); -- Jean Delvare -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
