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usb-serial: Fix timeout closing the device 

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 <jandryuk@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Message-id: 20200316174610.115820-5-jandryuk@gmail.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
Jason Andryuk 2020-03-16 13:46:10 -04:00 committed by Gerd Hoffmann
parent 30ad5fdd34
commit 647ee98772
1 changed files with 1 additions and 1 deletions
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2
hw/usb/dev-serial.c
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@ -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: