> > On Fri, 3 Aug 2012, B, Ravi wrote: > > > Alan, I did not understand, if the driver has unbound from > the device, > > what is the need to wait for 30seconds timeout to cancel the URB. > > Can you explain in detail. > > Consider a disk drive with a large cache. When usb-storage > unbinds from the device, the SCSI layer will want to tell the > disk to write out its cache. Flushing the cache could take a > while, so the SYNCHRONIZE CACHE command needs to have a long > timeout. Otherwise the contents of the cache could get lost. > Alan, what is meant by usb-stroage unbinds from the device? when the usb-storage unbinds from device, is it not when the device got disconnected? Or device gets umounted ? > > > > Why scsi to wait for 30 seconds timeout upon receiving > the DEVICE > > > > DICONNECT Notfication ? > > > > > > That's the timeout for all the SCSI commands. The > timeout doesn't > > > change when the disconnect notification is received. > > > > During disconnect, it is better to cancel all queued and active > > current URB, why to wait for 30sec timeout. > > It's not better. See above for an example where you _want_ > to wait for the command to finish. > > Now, if the device really has been unplugged then you can't > tell it to flush its cache. In that situation you really do > want to avoid the 30-second timeout. But neither usb-storage > nor the SCSI layer knows whether the device has been unplugged. > > However the host controller driver _does_ know (or at least, > it _should_ know). It should guarantee that all URBs fail > quickly when the device is not plugged in. It should not > wait forever for a DMA transfer that will never complete. > > That's why I suggested you fix the musb driver instead of > trying to change usb-storage. > The current MUSB HCD driver does not fail the URBs when the device got disconnected. > 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
