On 03/19/2013 10:25 PM, Henrik Rydberg wrote:

Hi Benjamin,

quoted

There is no need to register an input device containing no events.
This allows drivers using the quirk MULTI_INPUT to register one input
per report effectively used.

For backward compatibility, we need to add a quirk to request
this behavior.

Signed-off-by: Benjamin Tissoires <redacted>
---
 drivers/hid/hid-input.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/hid.h     |  1 +
 2 files changed, 78 insertions(+)

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index 21b196c..7aaf7d3 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c

@@ -1198,6 +1198,67 @@ static struct hid_input *hidinput_allocate(struct hid_device *hid)
 	return hidinput;
 }
 
+static bool hidinput_has_been_populated(struct hid_input *hidinput)
+{
+	int i;
+	bool r = 0;
+
+	for (i = 0; i < BITS_TO_LONGS(EV_CNT); i++)
+		r = r || hidinput->input->evbit[i];

I believe there is a bit count method that will do this for you (weight).

Actually, weight does not work here. evbit[] is an array of long, and we
still need to check if each field of this array is not null.

Thus, the following can be used (r being a long here):
r |= hidinput->input->evbit[i];

Cheers,
Benjamin