Re: [PATCH] Input: evdev - use monotonic clock for event timestamps

From: Chase Douglas
Date: Wed Oct 05 2011 - 10:35:21 EST

On 10/05/2011 10:23 AM, Henrik Rydberg wrote:
>> I understand your concern about breaking random drivers, and am hoping
>> that someon on this list could indicate whether this is a real concern
>> or not. To get a better feeling for possible regressions, I checked
>> xf86-input-evdev & -synaptics, and neither uses the evdev timestamp in
>> their current incarnations. Any idea what else might be a good place
>> to check?
> The input system is used for all sorts of events - switches, for
> instance. The point is that it is nearly impossible to know if
> something will break or not, hence the reluctance to modify interfaces.
>> One option is to make the evdev timestamp clock source a per-driver
>> configuration option (controllable from userspace?). This sounds like
>> it is doable, but would be significantly more complicated.
>> Another option would be to timestamp with monotonicraw + boottime +
>> sleeptime. This would be approximately wall clock time, but without
>> ntp and slew adjustments. But, I fear this would just make the rare
>> driver issue less obvious, since it would only become obvious when the
>> two clock sources started drifting apart.
> I agree, the problem is not really solvable. Dmitry?

We could put it into the -next tree early on in the cycle, and then it
will be in -next for a cycle and in Linus' tree for the real dev cycle.
By that time we would hope any issues would have emerged.

I'm not sure if that is a responsible approach. I agree that the change
would be good, but how sure would we be that nothing would break based
only on testing in development trees?

My personal thoughts are that I doubt it would cause issues. Based on
that gut feel, I would say that this approach is reasonable. However,
I'm just one voice in all this :).

-- Chase
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