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

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Date:	Tue, 14 Aug 2012 14:12:00 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Ping Cheng <pinglinux@...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 01:50:38PM -0700, Ping Cheng wrote:
> 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 ;-).

No, just generally busy ;(

> 
> 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?

I was talking about a bog-standard computer keyboard here.

> 
> 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().

input_estimate_events_per_packet() is a generic routine that is used for
all devices, not only [multi]touch.

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

But even that keyboard would have more than 10 keys, right? So even
though max_events should be 10 + 10 + 1 (10 keys, 10 msc, syn) your loop
would produce what 88 + 88 + 1 for full size music keyboard?

Thanks.

-- 
Dmitry
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