[v3] USB: serial: ftdi_sio: Add support for CBUS GPIO

Hi Johan,

On 4 August 2018 at 12:17, Loic Poulain [off-list ref] wrote:

Some FTDI devices like FTX or FT232R support CBUS Bit Bang mode on CBUS
pins, allowing host to control them via simple USB control transfers.
To make use of a CBUS pin in Bit Bang mode, the pin must be configured
to I/O mode in the FTDI EEPROM. This mode perfectly coexists with regular
USB to Serial function.

In this implementation, a GPIO controller is registered on FTDI probe
if at least one CBUS pin is configured for I/O mode. For now, only
FTX devices are supported.

This patch is based on previous Stefan Agner implementation tentative
on LKML [1].

[1] Message-Id: 1434838377-8042-1-git-send-email-stefan@agner.ch

Signed-off-by: Loic Poulain <redacted>

Any comments on this v3?

Regards,
Loic