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

[Henrik Rydberg <rydberg@euromail.se>]

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