[v5] USB: serial: ftdi_sio: implement GPIO support for FT-X devices

[Johan Hovold <johan@kernel.org>]

On Sun, Sep 23, 2018 at 06:03:30PM +0200, Karoly Pados wrote:
> This patch allows using the CBUS pins of FT-X devices as GPIO in CBUS
> bitbanging mode. There is no conflict between the GPIO and VCP
> functionality in this mode. Tested on FT230X and FT231X.
> 
> As there is no way to request the current CBUS register configuration
> from the device, all CBUS pins are set to a known state when the first
> GPIO is requested. This allows using libftdi to set the GPIO pins
> before loading this module for UART functionality, a behavior that
> existing applications might be relying upon (though no specific case
> is known to the authors of this patch).
> 
> Signed-off-by: Karoly Pados <pados@pados.hu>
> ---
> Changelog:
> - v2: Fix compile error when CONFIG_GPIOLIB is not defined.
> - v3: Incorporate review feedback.
> - v4: Include linux/gpio/driver.h unconditionally.
>       Replace and invert gpio_input with gpio_output.
>       Make ftdi_gpio_direction_get return 0/1.
>       Change dev_err msg in ftdi_set_bitmode_req.
>       Change formatting of error checking in ftdi_gpio_get.
>       Drop dev_err in ftdi_gpio_set.
>       Remove some line breaks and empty lines.
>       Change error handling in ftdi_read_eeprom (and adjust caller).
>       Replace SIO->FTX in FTDI_SIO_CBUS_MUX_GPIO macro name.
> - v5: Read only 4 bytes from eeprom in ftx_gpioconf_init.
>       Compare ftdi_read_eeprom result with 0 instead of eq. cehck.
>       Reserve 4 GPIOs even for FT234X.
>       Release CBUS after gpiochip deregister to avoid possible race.
>       Adjust comment on FTDI_SIO_SET_BITMODE macro.
>       Protect GPIO value/dir setting with mutex.

This patch doesn't add any locking so I'm assuming you posted the wrong
version of the patch.

>       Add support for gpiochip.get_multiple and set_multiple.
>       Add names to GPIO lines.

I'll wait for v6.

Thanks,
Johan