linux-kernel - Re: [PATCH 02/19] Input: Improve the events-per-packet estimate

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Date:	Tue, 14 Aug 2012 13:50:38 -0700
From:	Ping Cheng <pinglinux@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Henrik Rydberg <rydberg@...omail.se>,
	Jiri Kosina <jkosina@...e.cz>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/19] Input: Improve the events-per-packet estimate

On Tue, Aug 14, 2012 at 12:53 PM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> On Tuesday, August 14, 2012 12:32:21 PM Ping Cheng wrote:
>> On Sun, Aug 12, 2012 at 2:42 PM, Henrik Rydberg <rydberg@...omail.se> wrote:
>> > Many MT devices send a number of keys along with the mt information.
>> > This patch makes sure that there is room for them in the packet
>> > buffer.
>> >
>> > Signed-off-by: Henrik Rydberg <rydberg@...omail.se>
>> > ---
>> >
>> >  drivers/input/input.c | 10 +++++++---
>> >  1 file changed, 7 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/drivers/input/input.c b/drivers/input/input.c
>> > index 6e90705..8ebf116 100644
>> > --- a/drivers/input/input.c
>> > +++ b/drivers/input/input.c
>> > @@ -1777,6 +1777,9 @@ static unsigned int
>> > input_estimate_events_per_packet(struct input_dev *dev)>
>> >                 if (test_bit(i, dev->relbit))
>> >
>> >                         events++;
>> >
>> > +       /* Make room for KEY and MSC events */
>> > +       events += 7;
>>
>> Hi Henrik,
>>
>> It is nice to get rid of the redundant pieces and to incorporate
>> common functions. Thank you.
>>
>> I have a question about the code above though.  Why do we use 7
>> instead of going through the keys like:
>>
>>       for (i = 0; i < KEY_MAX; i++)
>>               if (test_bit(i, dev->keybit))
>>                       events++;
>
> Because that would result in gross over-estimation for many devices -
> my keyboard has 100+ keys but it never sends all of them in one event
> frame, not even if I can get a cat to lay on it ;)

Thanks for the prompt reply. I thought you were on vacation ;-).

So, what device are we talking about here? I thought it is a touch
device with a few extra buttons, which are reported as key events. Am
I missing something?

If it is a touch device, we won't have too many buttons. So,
test_bit(i, dev->keybit) won't be true for more than the number of
buttons that declared by __set_bit().

I would think we could play a keyboard (this keyboard does not have
letters on it ;-) with ten fingers.

Ping
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