Dear Jonathan Cameron, > On 12/08/2012 09:18 PM, Marek Vasut wrote: > > Dear Jonathan Cameron, > > > >> On 12/07/2012 03:24 PM, Marek Vasut wrote: > >>> This patch implements support for sampling of a touchscreen into > >>> the MXS LRADC driver. The LRADC block allows configuring some of > >>> it's channels into special mode where they either output the drive > >>> voltage or sample it, allowing it to operate a 4-wire or 5-wire > >>> resistive touchscreen. > >>> > >>> In case the touchscreen mode is enabled, the LRADC slot #7 is > >>> reserved for touchscreen only, therefore it is not possible to > >>> sample 8 LRADC channels at time, but only 7 channels. > >>> > >>> The touchscreen controller is configured such that the PENDOWN event > >>> disables touchscreen interrupts and triggers execution of worker > >>> thread, which then polls the touchscreen controller for X, Y and > >>> Pressure values. This reduces the overhead of interrupt-driven > >>> operation. Upon the PENUP event, the worker thread re-enables the > >>> PENDOWN detection interrupt and exits. > >>> > >>> Signed-off-by: Marek Vasut <marex@xxxxxxx> > >>> Cc: Fabio Estevam <fabio.estevam@xxxxxxxxxxxxx> > >>> Cc: Jonathan Cameron <jic23@xxxxxxxxxx> > >>> Cc: Shawn Guo <shawn.guo@xxxxxxxxxx> > >> > >> cc added for linux input and Dmitry. > >> > >> I'd like to gather some opinions on the best way to handle these touch > >> screen devices when are sharing some hardware with more generic adc's > >> as here. > >> > >> What we have is effectively a weird mulitplexing of different signals? > >> > >> So could we treat the various axis as separate channels of a normal > >> adc (even if they are infact coming from the same pins)? > > > > You can not. You also need to control voltage output to various plates to > > be able to sample it from the other plate. See the comment in my patch > > close to the big table explaining all this mayhem. > > Sure you need to play with the the 'real' channels to put voltages on the > right ones etc. This is special purpose hardware though so what I was > suggesting was to create 'virtual' channels associated with each axis. Whew! > These would then effectively do exactly what you are doing here in that > a 3 numbers would be generated to push on to input. It'd just be a little > less direct.... I'm not particularly sure it's a good idea, but it could > be done ;) See my previous email, maybe you can get one of those MX233 each-boards and connect some touchscreen to it ? It will provide you with insane controller and lot of fun for xmas ;-) > >> Then we could > >> have a go at having a generic touch screen driver acting as an IIO > >> consumer? (the interrupt driven IIO consumer stuff should be going in in > >> the comming merge window, but the example input driver didn't get > >> cleaned up in time.) > > > > That'd be very nice indeed. But as I said above, you'd need to add > > ability to control ADC channels so you can configure them as voltage > > outputs. That'd be fine, but I need to do such configuration thrice in > > one TS sampling cycle (I need to configure the TS for sampling X-axis, > > Y-axis and pressure). Add the overhead of reading the ADC channels via > > some interface instead of being able to directly trigger them. I'd hate > > to have laggy touchscreen pointer or my system spending too much time in > > kernel -- the kthread that samples the touchscreen already does consume > > some power. > > Yes there would indeed be some overhead and clearly you have some very > tight requirements here. It might be possible to do this with a low > enough overhead, I'm really not sure without trying it! > > > Also please consider the device with this LRADC is a 450MHz ARM system, > > so it has not much processing muscle. > > > > Besides (inbound rant), I suspect all this would add even more complexity > > to this already complex IIO stuff. > : > :) Sorry ;-) > >> The tricks in here with switching from interrupt triggered to polled is > >> a little nasty but I'll take your word for it that it is necessary! > > > > Let's bury this topic please, I'm still shedding bloody tears ... I spent > > two days trying to figure this part out. The hardware is nasty, period. > > You have my sympathy. Sometimes these hardware guys do seem to get carried > away :) They went all out here :( > >> As you have it sitting on a different delay channel you'd have to have > >> these 'magic channels' as a separate IIO device anyway. The scan > >> would then include all the magic channels. > > > > I got lost here. But anyway, this whole device behaves as a single IIO > > device so far providing only the ADCs, yes. > > Sure. If you did do the 'virtual' channel for each axis things suggested > above, it would be triggered separately from the adc channels. As we have > only one trigger (and triggered scan setup) per IIO device, this would > require a pair of them. This took me a bit to gurk down ;-) > >> Hmm. I'm not sure of the best way to handle this so fully > >> open to suggestions! > > > > I'm all ears as well. On the other hand, I'd love to have some sort of > > this implementation in 3.8 (is that even possible anymore?). > > Sadly no chance for 3.8 at this stage. Couple of weeks too late now. Ah ok. It's be nice though, it's not any critical part of kernel too. > >> In some ways perhaps it is better to conclude > >> these channels are so touch screen specific (when the hardware is > >> enabled) that it's better to do as you have done here. > > > > The idea sounds really good, I'm only afraid it's too much work with too > > little gain. And the overhead of this sollution is a bit worrying as > > well. > > Agreed. The overhead may be a problem particularly if we involve triggers > (which would require interrupt handling etc). Might be possible to work > without them here, but that would be fiddly. That reminds me of the ACPI ALS thing. Yep. > > NOTE: I'm a lazy bastard <--- does that count as a valid reason for not > > implementing it this way ? ;-) > > It is certainly a reason ;) Hehe :) > I only really brought this suggestion up as it is roughly I'd 'like' > to see touch screens handled. I have no issue with other solutions but > want to keep options open and if we were to change this over to something > close to what I suggest we would have an interesting issue as suddenly a > whole load more platform data would be needed (to tie the more generic > IIO bit to a touchscreen consumer driver). Yes, I agree with your point. > Anyhow, curriously enough none of my test boards have a screen let > alone a touch one so I'm hardly experienced in this area and so before > I merge this I would like some comments from the input side of things > (and an ACK from Dmitry). > > At least we have plenty of time before 3.9! [...] Thanks for the review and discussion! I'll send V2 as soon as I'm back home to test the adjustments! -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
