On Sat, Aug 17, 2024 at 10:28:51AM -0400, crwulff@xxxxxxxxx wrote: > From: Chris Wulff <Chris.Wulff@xxxxxxxxx> > > While supporting GET_REPORT is a mandatory request per the HID > specification the current implementation of the GET_REPORT request responds > to the USB Host with an empty reply of the request length. However, some > USB Hosts will request the contents of feature reports via the GET_REPORT > request. In addition, some proprietary HID 'protocols' will expect > different data, for the same report ID, to be to become available in the > feature report by sending a preceding SET_REPORT to the USB Device that > defines what data is to be presented when that feature report is > subsequently retrieved via GET_REPORT (with a very fast < 5ms turn around > between the SET_REPORT and the GET_REPORT). > > There are two other patch sets already submitted for adding GET_REPORT > support. The first [1] allows for pre-priming a list of reports via IOCTLs > which then allows the USB Host to perform the request, with no further > userspace interaction possible during the GET_REPORT request. And another > [2] which allows for a single report to be setup by userspace via IOCTL, > which will be fetched and returned by the kernel for subsequent GET_REPORT > requests by the USB Host, also with no further userspace interaction > possible. > > This patch, while loosely based on both the patch sets, differs by allowing > the option for userspace to respond to each GET_REPORT request by setting > up a poll to notify userspace that a new GET_REPORT request has arrived. To > support this, two extra IOCTLs are supplied. The first of which is used to > retrieve the report ID of the GET_REPORT request (in the case of having > non-zero report IDs in the HID descriptor). The second IOCTL allows for > storing report responses in a list for responding to requests. > > The report responses are stored in a list (it will be either added if it > does not exist or updated if it exists already). A flag (userspace_req) can > be set to whether subsequent requests notify userspace or not. > > Basic operation when a GET_REPORT request arrives from USB Host: > > - If the report ID exists in the list and it is set for immediate return > (i.e. userspace_req == false) then response is sent immediately, > userspace is not notified > > - The report ID does not exist, or exists but is set to notify userspace > (i.e. userspace_req == true) then notify userspace via poll: > > - If userspace responds, and either adds or update the response in > the list and respond to the host with the contents > > - If userspace does not respond within the fixed timeout (2500ms) > but the report has been set prevously, then send 'old' report > contents > > - If userspace does not respond within the fixed timeout (2500ms) > and the report does not exist in the list then send an empty > report > > Note that userspace could 'prime' the report list at any other time. > > While this patch allows for flexibility in how the system responds to > requests, and therefore the HID 'protocols' that could be supported, a > drawback is the time it takes to service the requests and therefore the > maximum throughput that would be achievable. The USB HID Specification > v1.11 itself states that GET_REPORT is not intended for periodic data > polling, so this limitation is not severe. > > Testing on an iMX8M Nano Ultra Lite with a heavy multi-core CPU loading > showed that userspace can typically respond to the GET_REPORT request > within 1200ms - which is well within the 5000ms most operating systems seem > to allow, and within the 2500ms set by this patch. > > [1] https://lore.kernel.org/all/20220805070507.123151-2-sunil@xxxxxxxxxxxxxxxxxxxx/ > [2] https://lore.kernel.org/all/20220726005824.2817646-1-vi@xxxxxxxxxxx/ > > Signed-off-by: David Sands <david.sands@xxxxxxxxx> > Signed-off-by: Chris Wulff <chris.wulff@xxxxxxxxx> > --- > v5: release spinlock on copy_from_user error path > v4: cleaned up a warning > https://lore.kernel.org/all/20240814125525.3917130-2-crwulff@xxxxxxxxx/ > v3: rebased to usb-next, checkpatch cleanup (formatting, lore.kernel.org links) > https://lore.kernel.org/all/20240810141834.640887-2-crwulff@xxxxxxxxx/ > v2: https://lore.kernel.org/all/CO1PR17MB541952864266039BAA7BBBD3E10F2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > v1: https://lore.kernel.org/all/20230215231529.2513236-1-david.sands@xxxxxxxxx/ Nice, thanks for sticking with this! greg k-h
