On Tue, Aug 13, 2024 at 4:38 AM Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Sat, Aug 10, 2024 at 10:18:35AM -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> > > --- > > v3: rebased to usb-next, checkpatch cleanup (formatting, lore.kernel.org links) > > v2: https://lore.kernel.org/all/CO1PR17MB541952864266039BAA7BBBD3E10F2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > v1: https://lore.kernel.org/all/20230215231529.2513236-1-david.sands@xxxxxxxxx/ > > --- > > drivers/usb/gadget/function/f_hid.c | 272 +++++++++++++++++++++++++++- > > include/uapi/linux/usb/g_hid.h | 40 ++++ > > include/uapi/linux/usb/gadgetfs.h | 2 +- > > 3 files changed, 306 insertions(+), 8 deletions(-) > > create mode 100644 include/uapi/linux/usb/g_hid.h > > Breaks the build: > > drivers/usb/gadget/function/f_hid.c:567:6: error: no previous prototype for ‘get_report_workqueue_handler’ [-Werror=missing-prototypes] > 567 | void get_report_workqueue_handler(struct work_struct *work) > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ > cc1: all warnings being treated as errors > I must not have warnings-as-errors enabled. I didn't notice the warning when I last built it. I will clean that up and make a new patch. -- Chris Wulff
