On 8/29/18 2:46 AM, Frederick Heinecke wrote:
Hello all,
Does anybody here know how the kernel handles externally multiplexed
peripherals and and what the proper way to setup the device tree for
multiplexed peripherals? For example, if I have two interfaces (say USB and
I2C) on the same pins, and I want both to be available and usable (not at the
same time of course), does the kernel natively support this or is this
something that needs to be written into the drivers for both interfaces? Could
the kernel or a user-space process potentially attempt to access both at the
same time?
Here's a poorly drawn example of what I'm asking about:
https://i.snag.gy/SJQnH1.jpg
Thank you,
Fred Heinecke
Hi Fred,
Recently I've been looking at a devices just act as you described. A FT232H
adapter. It has several interfaces including i2c, spi, jtag, etc but share some
pins. As far as I know these kind of devices should fall in mfd subsystem and as
for mfd subsystem, it handles devices with functions enabled together. Doing
what we want would need dynamic device register and unregister support. I;m just
planning to write a more support driver for FT232H and I handle this situation
with another sysfs entry 'current_mode', through this, I select which mode this
device should be working on. I haven't found any facility in kernel supports this.
Would you share what you device is? I think we can help you insight the
corresponding driver and check how did the manufacture do with it.
yours,
Song Qiang
