linux-kernel - Re: [PATCH 1/4] input: Set default events per packet.

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Message-ID: <AANLkTi=KotXd4TyyUrhMdKn3mEq+pz2ac3Vnraa5udFh@mail.gmail.com>
Date:	Fri, 25 Mar 2011 16:30:20 -0700
From:	Jeffrey Brown <jeffbrown@...roid.com>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] input: Set default events per packet.

On Fri, Mar 25, 2011 at 1:20 AM, Henrik Rydberg <rydberg@...omail.se> wrote:
>> +static inline bool is_mt_axis(int axis)
>> +{
>> +     return axis == ABS_MT_SLOT ||
>> +             (axis >= ABS_MT_FIRST && axis <= ABS_MT_LAST);
>> +}
>
> It would be great to get this inline into input/mt.h instead.

Makes sense.  I'll do that.

>> +     else if (test_bit(ABS_MT_TRACKING_ID, dev->absbit))
>> +             mt_slots = dev->absinfo[ABS_MT_TRACKING_ID].maximum -
>> +                     dev->absinfo[ABS_MT_TRACKING_ID].minimum + 1;
>
> This one is a bit iffy - the tracking id is not limited like this in
> mainline, looks like android usage. A test againts some arbitrary max
> should do it.

Yeah, I'm not sure about this one.  Tracking ID could effectively have
any range.  All of the MT Protocol A touch screen drivers I have
looked at, assuming they report tracking ids at all, report a
reasonable upper bound on the contact points they support.

Originally, I set an arbitrary maximum bound of 20 slots.  In the
interests of keeping it simple, I decided to remove that bound when I
submitted the patch for review here.

How about:

mt_slots = min(MAX_MT_SLOTS_TO_INFER_FROM_TRACKING_ID_RANGE,
   dev->absinfo[ABS_MT_TRACKING_ID].maximum -
dev->absinfo[ABS_MT_TRACKING_ID].minimum + 1);

Where MAX_MT_SLOTS_TO_INFER_FROM_TRACKING_ID_RANGE is set to 32 or something.

There's also the question of how many slots we should infer when
neither ABS_MT_SLOT or ABS_MT_TRACKING_ID is available.  The drivers
I've seen that don't provide tracking ids, are very basic and tend to
only support 2 touch points.

I guess we could add a DEFAULT_NUMBER_OF_MT_SLOTS constant to handle that case.

Please feel free to suggest better names for these constants.

Jeff.
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