[PATCH] Input: document inhibiting

Andrzej Pietrasiewicz
2020-06-16T17:29:26Z

Document inhibiting input devices and its relation to being
a wakeup source.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
---

@Hans, @Dmitry,

My fist attempt at documenting inhibiting. Kindly look at it to see if I haven't got anything
wrong.

Andrzej

Documentation/input/input-programming.rst | 36 +++++++++++++++++++++++
1 file changed, 36 insertions(+)

diff --git a/Documentation/input/input-programming.rst b/Documentation/input/input-programming.rst
index 45a4c6e05e39..0cd1ad4504fb 100644
--- a/Documentation/input/input-programming.rst
+++ b/Documentation/input/input-programming.rst
@@ -164,6 +164,42 @@ disconnects. Calls to both callbacks are serialized.
The open() callback should return a 0 in case of success or any nonzero value
in case of failure. The close() callback (which is void) must always succeed.

+Inhibiting input devices
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Inhibiting a device means ignoring input events from it. As such it is about maintaining
+relationships with input handlers - either an already existing relationships, or
+relationships to be established while the device is in inhibited state.
+
+If a device is inhibited, no input handler will receive events from it.
+
+The fact that nobody wants events from the device is exploited further, by calling device's
+close() (if there are users) and open() (if there are users) on inhibit and uninhibit
+operations, respectively. Indeed, the meaning of close() is to stop providing events
+to the input core and that of open() is to start providing events to the input core.
+
+Inhibiting and uninhibiting is orthogonal to opening and closing the device by input
+handlers. Userspace might want to inhibit a device in anticipation before any handler is
+positively matched against it.
+
+Inhibiting and uninhibiting is orthogonal to device's being a wakeup source, too. Being a
+wakeup source plays a role when the system is sleeping, not when the system is operating.
+How drivers should program their interaction between inhibiting, sleeping and being a wakeup
+source is driver-specific.
+
+Taking the analogy with the network devices - bringing a network interface down doesn't mean
+that it should be impossible to be wake the system up on LAN through this interface. So, there
+may be input drivers which should be considered wakeup sources even when inhibited. Actually,
+in many i2c input devices their interrupt is declared a wakeup interrupt and its handling
+happens in driver's core, which is not aware of input-specific inhibit (nor should it be).
+Composite devices containing several interfaces can be inhibited on a per-interface basis and
+e.g. inhibiting one interface shouldn't affect the device's capability of being a wakeup source.
+
+If a device is to be considered a wakeup source while inhibited, special care must be taken when
+programming its suspend(), as it might need to call device's open(). Depending on what close()
+means for the device in question not opening() it before going to sleep might make it impossible
+to provide any wakeup events. The device is going to sleep anyway.
+
Basic event types
~~~~~~~~~~~~~~~~~

--
2.17.1