Re: [PATCH] USB: serial: ftdi_sio: Fix serial port stall after resume

Johan Hovold
2020-10-08T15:21:13Z

On Tue, Sep 29, 2020 at 09:33:27PM +0200, Helge Deller wrote:
> With a 4-port serial USB HUB with FT232BM chips the serial ports stop
> working after a software suspend/resume cycle.
> Rewriting the latency timer during the resume phase fixes it.

Hmm. This sounds weird. Why would the latency timer make such a
difference?

> Cc: stable@vger.kernel.org
> Signed-off-by: Helge Deller <deller@gmx.de>
>
> diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
> index 9823bb424abd..8ee6cf6215c1 100644
> --- a/drivers/usb/serial/ftdi_sio.c
> +++ b/drivers/usb/serial/ftdi_sio.c
> @@ -1092,6 +1092,7 @@ static u32 ftdi_232bm_baud_base_to_divisor(int baud, int base);
> static u32 ftdi_232bm_baud_to_divisor(int baud);
> static u32 ftdi_2232h_baud_base_to_divisor(int baud, int base);
> static u32 ftdi_2232h_baud_to_divisor(int baud);
> +static int ftdi_reset_resume(struct usb_serial *serial);
>
> static struct usb_serial_driver ftdi_sio_device = {
> .driver = {
> @@ -1122,6 +1123,7 @@ static struct usb_serial_driver ftdi_sio_device = {
> .set_termios = ftdi_set_termios,
> .break_ctl = ftdi_break_ctl,
> .tx_empty = ftdi_tx_empty,
> + .reset_resume = ftdi_reset_resume,
> };
>
> static struct usb_serial_driver * const serial_drivers[] = {
> @@ -2379,6 +2381,16 @@ static int ftdi_stmclite_probe(struct usb_serial *serial)
> return 0;
> }
>
> +static int ftdi_reset_resume(struct usb_serial *serial)
> +{
> + struct usb_serial_port *port = serial->port[0];
> +
> + if (tty_port_initialized(&port->port))
> + write_latency_timer(port);

Why are you only doing this for open ports?

> +
> + return usb_serial_generic_resume(serial);
> +}

And if the device has been reset there may need to reconfigured the
termios settings for open ports.

Could you expand a bit on what the problem is here?

Johan