On Fri, 8 Oct 2010 19:03:27 -0700, Rory Filer wrote: > > > I'm assuming that a kernel space chip driver like our gpio expander > > (pca953x.c) also uses the same adapter driver as my user-space > > application since that expander chip is on the same bus. > > > > Let's clarify right away: i2c-dev (which handles /dev/i2c-* nodes) is > > NOT an adapter driver. It is a bridge driver between user-space and > > your adapter driver. Your adapter driver is most likely one living in > > drivers/i2c/busses, and depends on the actual hardware you run on. > > OK, thanks that's clear. I was confused by the terminology in the > dev-interface document. When it said to open an adapter, I thought > that meant I was using the associated adapter driver. Well, you end up using the underlying adapter driver. i2c-dev is only a glue driver between user-space and the actual in-kernel i2c adapter driver. See https://i2c.wiki.kernel.org/index.php/Driver_Architecture for a diagram of the architecture. > > Incorrect. The address isn't written to the adapter, it is a setting > > local to i2c-dev and even specific to the file handle you got when > > opening a /dev/i2c-* node. Each subsequent read, write or smbus call in > > your user-space driver automatically includes the slave address, which > > is only valid for the read, write or smbus call in question. I realize my wording may be a little misleading. When you set a slave address using the I2C_SLAVE ioctl, the address is valid for _all_ subsequent read, write or smbus calls on the filehandle, until either the file is closed or ioctl(I2C_SLAVE) is called again, not only the following one. > Excellent! - in the words of a famous Swiss restaurant's wine menu, this > leaves me nothing to hope for! > > Jean, thank you for your help, it saved me a ton pouring over source > code and allowed me to get on with the job at hand. Much appreciated. You're welcome. -- Jean Delvare http://khali.linux-fr.org/wishlist.html -- 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
