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[PATCH 4/4] usb-serial: Fix timeout closing the device
From: |
Jason Andryuk |
Subject: |
[PATCH 4/4] usb-serial: Fix timeout closing the device |
Date: |
Thu, 12 Mar 2020 08:55:23 -0400 |
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>
---
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
- [PATCH 0/4] usb-serial: xHCI and timeout fixes, Jason Andryuk, 2020/03/12
- [PATCH 1/4] usb-serial: Move USB_TOKEN_IN into a helper function, Jason Andryuk, 2020/03/12
- [PATCH 2/4] usb-serial: chunk data to wMaxPacketSize, Jason Andryuk, 2020/03/12
- [PATCH 3/4] usb-serial: Increase receive buffer to 496, Jason Andryuk, 2020/03/12
- [PATCH 4/4] usb-serial: Fix timeout closing the device,
Jason Andryuk <=
- Re: [PATCH 0/4] usb-serial: xHCI and timeout fixes, no-reply, 2020/03/12
- Re: [PATCH 0/4] usb-serial: xHCI and timeout fixes, no-reply, 2020/03/12