On Wed, 7 Mar 2007, Sarah Bailey wrote: > What transfer flags should usbfs2 expect userspace to set? > > I have opinions on most of the transfer flas, but I'm unsure about > URB_NO_FSBR. usbfs allows it to be set, although it looks like a hack > since the other flags are redefined as USBDEVFS_* and that one isn't. > LDD3 says this flag is only used by the uhci host controller driver. > Why was this exposed in usbfs?
I don't know about usbfs. It goes back to the earlier days of Linux USB support, when UHCI was relatively more important than it is now. In any case, URB_NO_FSBR is merely a minor optimization and it can safely be ignored. > Also, could some USB gurus check my initial opinions on the other > transfer flags: > > Userspace shouldn't be allowed to set URB_NO_TRANSFER_DMA_MAP and > URB_NO_SETUP_DMA_MAP, since usbfs2 should set the policy on whether > usbfs2 or the USB core does DMA mapping. Correct. > URB_NO_INTERRUPT also should be disallowed, since my code relies on > the URB completion function being called for every URB. Probably true. Unless you want to support some mode in which userspace submits a whole sequence of URBs for a single endpoint and gets notified only when all of them are complete. In that case all of the URBs except the last would have that flag set. > URB_SHORT_NOT_OK is redundant, since userspace can detect a short read > from the return value of the system call. Or is there a deeper reason > for setting this flag? There is. It's there for handling the situation described above, where a sequence of URBs is submitted at once. If one of them gets a short reply then that flag will cause an error, so the remaining URBs can be unlinked instead of blindly proceding. > URB_ISOC_ASAP should be used automatically, unless the user specifies > the start frame through an ioctl. Yes. However the ISO API has been under discussion for changes. See http://marc.theaimsgroup.com/?l=linux-usb-devel&m=116233077631176&w=2 > URB_ZERO_PACKET should be allowed for buggy hardware. However, it seems > like this should be a per-endpoint (or per-device) flag, rather than a > per-URB flag. It would be nice if there was a file in sysfs so that > there could be a udev rule to set this flag. No, URB_ZERO_PACKET is not intended for buggy hardware. It is meant for situations where the host will send less data than the device expects to receive. As such it has to be per-URB, not per-device or per-endpoint. Alan Stern ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
