Re: Xilinx iic i2c bus interface GPIO support for i2c-mux in Linux.

[Robin Holt <holt-sJ/iWh9BUns@public.gmane.org>]

On Wed, Feb 08, 2012 at 08:54:29PM +0100, Jean Delvare wrote:
> Hi Robin,
> 
> On Wed, 8 Feb 2012 13:46:15 -0600, Robin Holt wrote:
> > We are using a Xilinx FPGA which implements a series of i2c bus
> > interfaces.  We are planning on implementing a single-bit GPIO
> > (XIIC_GPO_REG_OFFSET) which is included in that logic block to act
> > as a MUX selector (also in the FPGA) between two separate i2c busses.
> > 
> > This will require a GPIO driver in the linux kernel.
> > 
> > Is it better to try and change the i2c-xiic.c code which already knows
> > about the GPO register to handle that additional GPIO or should we be
> > implementing the GPIO driver outside the i2c driver and then use the
> > standard i2c-mux support available in newer kernels?
> 
> Both are possible. It depends if there are other GPIOs on your FPGA
> which you will have to access from other drivers for other purposes. If
> there are such other GPIOs then it certainly makes sense to have a
> clean, separate gpio driver for your FPGA, and have all consumers bind
> to it. If not, then I'd keep things simple and embed everything in
> i2c-xiic.c, especially if the two i2c buses are truly separated and
> there is no common trunk (i2c-mux would create 3 segments.)

Do you know of any other examples of an i2c bus interface which provides
a built-in general purpose output for MUX selection?  I am hoping for
some example of the "right" way to do this.

Thanks,
Robin