Re: [PATCH 4/4] usb-serial: Fix timeout closing the device

[Samuel Thibault]

Jason Andryuk, le jeu. 12 mars 2020 08:55:23 -0400, a ecrit:
> Linux guests wait ~30 seconds when closing the emulated /dev/ttyUSB0.
> During that time, the kernel driver is sending many control URBs
> requesting GetModemStat (5).  Real hardware returns a status with
> FTDI_THRE (Transmitter Holding Register) and FTDI_TEMT (Transmitter
> Empty) set.  QEMU leaves them clear, and it seems Linux is waiting for
> FTDI_TEMT to be set to indicate the tx queue is empty before closing.
> 
> Set the bits when responding to a GetModemStat query and avoid the
> shutdown delay.
> 
> Signed-off-by: Jason Andryuk <address@hidden>

Reviewed-by: Samuel Thibault <address@hidden>

> ---
> Looking at a USB dump for a real FTDI USB adapter, I see these bits set
> in all the bulk URBs where QEMU currently has them clear.
> ---
>  hw/usb/dev-serial.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/usb/dev-serial.c b/hw/usb/dev-serial.c
> index ef33bcd127..5389235f17 100644
> --- a/hw/usb/dev-serial.c
> +++ b/hw/usb/dev-serial.c
> @@ -332,7 +332,7 @@ static void usb_serial_handle_control(USBDevice *dev, 
> USBPacket *p,
>          break;
>      case DeviceInVendor | FTDI_GET_MDM_ST:
>          data[0] = usb_get_modem_lines(s) | 1;
> -        data[1] = 0;
> +        data[1] = FTDI_THRE | FTDI_TEMT;
>          p->actual_length = 2;
>          break;
>      case DeviceOutVendor | FTDI_SET_EVENT_CHR:
> -- 
> 2.24.1
> 

-- 
Samuel
c> ah (on trouve fluide glacial sur le net, ou il faut aller dans le monde reel 
?)
s> dans le monde reel
c> zut