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author | David Herrmann <dh.herrmann@googlemail.com> | 2012-06-10 15:16:25 +0200 |
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committer | Jiri Kosina <jkosina@suse.cz> | 2012-06-18 13:42:03 +0200 |
commit | fcfcf0deb89ece6eb9ae23768fec1bc1718f9b7f (patch) | |
tree | fcf86b0c55d4feea91ee00a6e59c423b6442708a /Documentation/hid | |
parent | 3b3baa82e4306b5160692643fab2fa322ceb94f9 (diff) | |
download | kernel_goldelico_gta04-fcfcf0deb89ece6eb9ae23768fec1bc1718f9b7f.zip kernel_goldelico_gta04-fcfcf0deb89ece6eb9ae23768fec1bc1718f9b7f.tar.gz kernel_goldelico_gta04-fcfcf0deb89ece6eb9ae23768fec1bc1718f9b7f.tar.bz2 |
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>
Diffstat (limited to 'Documentation/hid')
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