Re: [RFC][PATCH] Input: Add infrastrucutre for monotonic event time stamps.

[Chase Douglas <chase.douglas@canonical.com>]

On 01/05/2012 04:19 PM, John Stultz wrote:
> On Thu, 2012-01-05 at 15:54 -0800, Chase Douglas wrote:
>> On 01/05/2012 03:28 PM, Dmitry Torokhov wrote:
>>> Hi John,
>>>
>>> On Thu, Jan 05, 2012 at 03:01:05PM -0800, John Stultz wrote:
>>>>  
>>>> +	case EVIOCMONTIME:
>>>> +		if (copy_from_user(&i, p, sizeof(unsigned int)))
>>>> +			return -EFAULT;
>>>> +		client->use_monotonic = i;
>>>> +		return 0;
>>>
>>> Maybe we should let users pass not boolean but CLOCK_* value (and reject
>>> ones that we do not support) ? This way if someone wants to use some
>>> other clock type in the future we won't need new ioctl.
>>
>> Could we also find a way to specify device time? Apple's Magic Mouse and
>> Magic Trackpad spit out events with their own timestamps. Maybe there
>> would be other devices that would support high accuracy timestamps too?
> 
> The dynamic posix clocks stuff already supports this sort of thing for
> PTP, but its driver by driver, and its not all that clear that you can
> read the device timestamp any old time you want (I suspect they're all
> tied to device events). So it won't quite work for a clock_gettime()
> style usage.
> 
> I don't really know what the best way to do this would be. We could
> overload a negative clockid value, since you're not going to be wanting
> thread cputime for device timestamps. But that's not super elegant
> either.
> 
> But just having a specified clock id via the ioctl makes something like
> what you're proposing possible.  Just a matter of how to cleanly specify
> device timestamps against all the other possible ids.

I guess this is mostly what I'm after right now. I have no plans on
implementing device timestamps, and I don't even really have time to
think about it much right now :). As long as we have a plan for how we
could specify it in the future, if someone wanted to implement it, then
I'm happy.

-- Chase