USB: serial: cp210x: Fix GPIO in autosuspend

[Johan Hovold <johan@kernel.org>]

On Mon, Jan 14, 2019 at 08:43:52PM +0100, Karoly Pados wrote:
> Current GPIO code in cp210x fails to take USB autosuspend into account,
> making it practically impossible to use GPIOs with autosuspend enabled
> without user configuration. Fix this like for ftdi_sio in a previous patch.
> Tested on a CP2102N.
> 
> Signed-off-by: Karoly Pados <pados@pados.hu>
> ---
>  drivers/usb/serial/cp210x.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> index c0777a374a88..8f974eabce63 100644
> --- a/drivers/usb/serial/cp210x.c
> +++ b/drivers/usb/serial/cp210x.c
> @@ -598,9 +598,15 @@ static int cp210x_read_vendor_block(struct usb_serial *serial, u8 type, u16 val,
>  	void *dmabuf;
>  	int result;
>  
> +	result = usb_autopm_get_interface(serial->interface);
> +	if (result)
> +		return result;
> +

> @@ -702,9 +709,15 @@ static int cp210x_write_vendor_block(struct usb_serial *serial, u8 type,
>  	void *dmabuf;
>  	int result;
>  
> +	result = usb_autopm_get_interface(serial->interface);
> +	if (result)
> +		return result;
> +

I think it's better to add the autopm call to gpio210x_gpio_get/set
only. This will allow for a simpler patch, and keeps the autopm handling
confined to the gpio paths.

> @@ -1383,6 +1397,7 @@ static void cp210x_gpio_set(struct gpio_chip *gc, unsigned int gpio, int value)
>  	} else {
>  		u16 wIndex = buf.state << 8 | buf.mask;
>  
> +		usb_autopm_get_interface(serial->interface);

Also make sure to always check for errors from autopm_get().

>  		result = usb_control_msg(serial->dev,
>  					 usb_sndctrlpipe(serial->dev, 0),
>  					 CP210X_VENDOR_SPECIFIC,

Thanks,
Johan