linux-kernel - Re: [PATCH 1/7] HID: input: don't register unmapped input devices

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Date:	Fri, 22 Mar 2013 15:48:37 +0100
From:	Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:	Henrik Rydberg <rydberg@...omail.se>
CC:	Benjamin Tissoires <benjamin.tissoires@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...c.fr>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] HID: input: don't register unmapped input devices

On 03/19/2013 10:25 PM, Henrik Rydberg wrote:
> Hi Benjamin,
> 
>> 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 <benjamin.tissoires@...hat.com>
>> ---
>>  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
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