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usb: thoughts of adding more support for FT232H

Hi Johan,

I've been developing some iio device drivers and found that some people
would like to test their devices with a qemu system which requires an
i2c or spi port on our development hosts. Usually this is achieved with
a DLN-2 adapter, while this is a bit difficult for me because it costs
~175$ in my country. Then I found that FTDI's FT232H supports both these
two modes and costs only less than 5$ but without full support in kernel.
The ftdi-sio driver supports FT232H only as a serial converter.
So I'm planning to write a mfd driver for it supports both these three
modes, here are my thoughts:
 - This device cannot support these three modes together because they
   share some common pins, so I'm planning to add a sysfs entry
   'current_mode' for selecting which mode the device should be working
 - This device is in uart mode on reset, so default mode would be reset,
   too. This also helps for people only want to use this as a serial
   converter feels nothing has happened (compatible).
 - I was trying to reuse the ftdi-sio driver but it seems like mfd can
   only register platform devices, while this is a usb driver. I may
   have to copy some functions from this driver.

Would you share any ideas? I'd appreciate it.


Song Qiang