linux-kernel - usb: thoughts of adding more support for FT232H

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Message-ID: <48bc71bb-68e4-8b29-f609-940c9aedc0a9@gmail.com>
Date:   Wed, 5 Dec 2018 22:10:40 +0800
From:   Song Qiang <songqiang1304521@...il.com>
To:     johan@...nel.org, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: 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
    on.
  - 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.

yours,

Song Qiang