HID: uhid: allow poll()'ing on uhid devices

As long as the internal buffer is not empty, we return POLLIN to
user-space.

uhid->head and uhid->tail are no atomics so the comparison may return
inexact results. However, this doesn't matter here as user-space would
need to poll() in two threads simultaneously to trigger this. And in this
case it doesn't matter if a cached result is returned or the exact new
result as user-space does not know which thread returns first from poll()
and the following read(). So it is safe to compare the values without
locking.

Change-Id: I42a43907d2f8eedf4ae941261c56e98ed0489db6
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: implement read() on uhid devices

User-space can use read() to get a single event from uhid devices. read()
does never return multiple events. This allows us to extend the event
structure and still keep backwards compatibility.

If user-space wants to get multiple events in one syscall, they should use
the readv()/writev() syscalls which are supported by uhid.

This introduces a new lock which helps us synchronizing simultaneous reads
from user-space. We also correctly return -EINVAL/-EFAULT only on errors
and retry the read() when some other thread captured the event faster than
we did.

Change-Id: Ic20ddd97aa61813b68011c6591f748332a920c0e
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: implement write() on uhid devices

Similar to read() you can only write() a single event with one call to an
uhid device. To write multiple events use writev() which is supported by
uhid.

We currently always return -EOPNOTSUPP but other events will be added in
later patches.

Change-Id: Ibab7470e2e780d28e0e4506f3e51a6278b729cc5
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: add UHID_CREATE and UHID_DESTROY events

UHID_CREATE and UHID_DESTROY are used to create and destroy a device on an
open uhid char-device. Internally, we allocate and register an HID device
with the HID core and immediately start the device. From now on events may
be received or sent to the device.

The UHID_CREATE event has a payload similar to the data used by
Bluetooth-HIDP when creating a new connection.

Change-Id: If74ef6d1e82546edb4e9d5909ea9f173dcad2aa6
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: allow feeding input data into uhid devices

This adds a new event type UHID_INPUT which allows user-space to feed raw
HID reports into the HID subsystem. We copy the data into kernel memory
and directly feed it into the HID core.

There is no error handling of the events couldn't be parsed so user-space
should consider all events successfull unless read() returns an error.

Change-Id: Ia1c9858a11a3bcf372e10f11c0972a070f7c518a
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: forward hid report-descriptor to hid core

When the uhid_hid_parse callback is called we simply forward it to
hid_parse_report() with the data that we got in the UHID_CREATE event.

Change-Id: Ie60e5d88c0d7f16d54677851fe043cf5188f001d
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: add UHID_START and UHID_STOP events

We send UHID_START and UHID_STOP events to user-space when the HID core
starts/stops the device. This notifies user-space about driver readiness
and data-I/O can start now.

This directly forwards the callbacks from hid-core to user-space.

Change-Id: I993fff137f468027b56dad02f45cd459d40f15e6
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: forward open/close events to user-space

HID core notifies us with *_open/*_close callbacks when there is an actual
user of our device. We forward these to user-space so they can react on
this. This allows user-space to skip I/O unless they receive an OPEN
event. When they receive a CLOSE event they can stop I/O again to save
energy.

Change-Id: I19dfd27cb97a8bd9989530f4053b241397ef6752
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: forward output request to user-space

If the hid-driver wants to send standardized data to the device it uses a
linux input_event. We forward this to the user-space transport-level
driver so they can perform the requested action on the device.

Change-Id: Iee23bac4dcb6b38e795aca3f2310ff28e792524a
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
HID: uhid: forward raw output reports to user-space

Some drivers that use non-standard HID features require raw output reports
sent to the device. We now forward these requests directly to user-space
so the transport-level driver can correctly send it to the device or
handle it correspondingly.

There is no way to signal back whether the transmission was successful,
moreover, there might be lots of messages coming out from the driver
flushing the output-queue. However, there is currently no driver that
causes this so we are safe. If some drivers need to transmit lots of data
this way, we need a method to synchronize this and can implement another
UHID_OUTPUT_SYNC event.

Change-Id: I198c836e779888e6e33cc6d7ade763d613e20c85
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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.

Change-Id: Ifa4ea94e559501c9dcd6e70a6ab50d3277d6398b
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>