From: David Herrmann <dh.herrmann@gmail.com>
Date: Mon, 2 Sep 2013 11:58:09 +0000 (+0200)
Subject: hog: ignore UHID-setup events and document why
X-Git-Tag: android-x86-4.4-r3~7680
X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=8a8a49941e2112f538904e9e6ed828f37e966013;p=android-x86%2Fexternal-bluetooth-bluez.git

hog: ignore UHID-setup events and document why

The UHID_{START,STOP,OPEN,CLOSE} events should be ignored by us to avoid
triggering the warn(). It is safe to do that. Add few comments that
explain why we don't have to handle these.
---

diff --git a/profiles/input/hog.c b/profiles/input/hog.c
index 91c2802f4..4647fefba 100644
--- a/profiles/input/hog.c
+++ b/profiles/input/hog.c
@@ -621,12 +621,43 @@ static gboolean uhid_event_cb(GIOChannel *io, GIOCondition cond,
 	DBG("uHID event type %d received", ev.type);
 
 	switch (ev.type) {
+	case UHID_START:
+	case UHID_STOP:
+		/* These are called to start and stop the underlying hardware.
+		 * For HoG we open the channels before creating the device so
+		 * the hardware is always ready. No need to handle these.
+		 * Note that these are also called when the kernel switches
+		 * between device-drivers loaded on the HID device. But we can
+		 * simply keep the hardware alive during transitions and it
+		 * works just fine.
+		 * The kernel never destroys a device itself! Only an explicit
+		 * UHID_DESTROY request can remove a device. */
+		break;
+	case UHID_OPEN:
+	case UHID_CLOSE:
+		/* OPEN/CLOSE are sent whenever user-space opens any interface
+		 * provided by the kernel HID device. Whenever the open-count
+		 * is non-zero we must be ready for I/O. As long as it is zero,
+		 * we can decide to drop all I/O and put the device
+		 * asleep This is optional, though. Moreover, some
+		 * special device drivers are buggy in that regard, so
+		 * maybe we just keep I/O always awake like HIDP in the
+		 * kernel does. */
+		break;
 	case UHID_OUTPUT:
 	case UHID_FEATURE:
 		forward_report(hogdev, &ev);
 		break;
 	case UHID_OUTPUT_EV:
-		DBG("uHID output event: type %d code %d value %d",
+		/* This is only sent by kernels prior to linux-3.11. It
+		 * requires us to parse HID-descriptors in user-space to
+		 * properly handle it. This is redundant as the kernel
+		 * does it already. That's why newer kernels assemble
+		 * the output-reports and send it to us via UHID_OUTPUT.
+		 * We never implemented this, so we rely on users to use
+		 * recent-enough kernels if they want this feature. No reason
+		 * to implement this for older kernels. */
+		DBG("Unsupported uHID output event: type %d code %d value %d",
 			ev.u.output_ev.type, ev.u.output_ev.code,
 			ev.u.output_ev.value);
 		break;