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authorDavid Herrmann <dh.herrmann@googlemail.com>2012-06-10 15:16:25 +0200
committerJiri Kosina <jkosina@suse.cz>2012-06-18 13:42:03 +0200
commitfcfcf0deb89ece6eb9ae23768fec1bc1718f9b7f (patch)
treefcf86b0c55d4feea91ee00a6e59c423b6442708a /Documentation/hid
parent3b3baa82e4306b5160692643fab2fa322ceb94f9 (diff)
HID: uhid: implement feature requests
HID standard allows sending a feature request to the device which is answered by an HID report. uhid implements this by sending a UHID_FEATURE event to user-space which then must answer with UHID_FEATURE_ANSWER. If it doesn't do this in a timely manner, the request is discarded silently. We serialize the feature requests, that is, there is always only a single active feature-request sent to user-space, other requests have to wait. HIDP and USB-HID do it the same way. Because we discard feature-requests silently, we must make sure to match a response to the corresponding request. We use sequence-IDs for this so user-space must copy the ID from the request into the answer. Feature-answers are ignored if they do not contain the same ID as the currently pending feature request. Internally, we must make sure that feature-requests are synchronized with UHID_DESTROY and close() events. We must not dead-lock when closing the HID device, either, so we have to use separate locks. Signed-off-by: David Herrmann <dh.herrmann@googlemail.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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