On Thu, May 20, 2010 at 10:13:24AM +1000, Peter Hutterer wrote: > On Wed, May 19, 2010 at 02:12:14PM +0200, Henrik Rydberg wrote: > > Peter Hutterer wrote: > > > On Tue, May 18, 2010 at 10:10:29PM +0200, Henrik Rydberg wrote: > > >> This patch adds documentation for the SYN_MT_SLOT event and gives > > >> examples of how to use the event slot protocol. > > > > > > thanks, this is really nice documentation! the approach seems good, though I > > > do have a few questions inline. > > > > > [...] > > > > > > Is there a limit on the number of slots? > > > > The slots are dynamically allocated by the driver, so there is no practical > > limit. Each slot currently takes 44 bytes, and allocating a few kilobytes of > > kernel memory is not a problem. > > > > > 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). -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
