linux-kernel - Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev2)

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Date:	Thu, 20 May 2010 12:46:17 +0200
From:	Henrik Rydberg <rydberg@...omail.se>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Peter Hutterer <peter.hutterer@...-t.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mika Kuoppala <mika.kuoppala@...ia.com>,
	Benjamin Tissoires <tissoire@...a.fr>,
	Stephane Chatty <chatty@...c.fr>,
	Rafi Rubin <rafi@...s.upenn.edu>,
	Michael Poole <mdpoole@...ilus.org>
Subject: Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev2)

Dmitry Torokhov wrote:
>>>> Will all drivers with ABS_MT_TRACKING_ID use slots? if not, how can I know
>>>> in advance if a device may use slots or not?
>>> Eventually, this might become true, but you are pointing at one of the weaker
>>> points of the current setup. There is no bit field for the EV_SYN events, so
>>> there is no way to know in advance if SYN_MT_SYNC or SYN_MT_SLOT is used. This
>>> could quite possibly be added to the EVIO interface. Meanwhile, the method I use
>>> is to detect the first SYN_MT_SLOT and select parser based on that information.
>> I'd really prefer if there was some way to detect this. While I'm not quite
>> sure how the matching X drivers would look like it's likely that the setups
>> will be different for drivers that support slots and those that don't.
>> e.g. those that don't have slots simply send events as valuators, those that
>> do may split into multiple devices.
>>
>> Doing this at runtime - after the device has been set up is...tricky.
>>
> 
> Right, I think we should try our hardest to allow userspace base
> protocol decoding decisions on device capabilities and not the event
> datastream. What about moving from SYN_MT_SLOT to ABS_MT_SLOT? I think
> it makes more sense since it is not a simple marker but carries data
> (slot number).

I agree, it both makes sense and resolves two issues. Will change.

Cheers,
Henrik

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