On Tue, 16 Mar 2010, Jason Wessel wrote: > This patch tries to solve the problem that data is lost because there > are too many outstanding transmit urb's while trying to execute > printk's to a console. The same is true if you try something like > "echo t > /proc/sysrq-trigger". > > This patch takes the route of forcibly polling the hcd device to drain > the urb queue in order to initiate the bulk write call backs. This > only happens if the device is a usb serial console device that sets > the max_in_flight_urbs to a non zero value in the serial device > structure. > > A few millisecond penalty will get incurred to allow the hcd controller > to complete a write urb, else the console data is thrown away. > > The max_in_flight_urbs was reduced in the usb_debug driver because it > is highly desired to push things out to the console in a timely > fashion and there is no need to have a queue that large for the > interrupt driven mode of operation when used through the tty > interface. > diff --git a/include/linux/usb.h b/include/linux/usb.h > index 8c9f053..a7d6cf7 100644 > --- a/include/linux/usb.h > +++ b/include/linux/usb.h > @@ -569,6 +569,9 @@ static inline void usb_mark_last_busy(struct usb_device *udev) > > /*-------------------------------------------------------------------------*/ > > +/* for polling the hcd device */ > +extern void usb_poll_irq(struct usb_device *udev); > + The points Johan Hovold made about max_in_flight_urbs are well taken and they should be addressed before this patch is accepted. The parts about usb_poll_irq() are fine, although the comment above should be changed to something more like: /* for polling the device's host controller */ since "hcd" is short for "host controller driver", and "polling the host controller driver device" doesn't make much sense. The same goes for the comment in usb_do_console_write(). Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
