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. > > > 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. 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
