On 10/27/2014 08:02 PM, Griffis, Brad wrote:
> On 10/27/2014 12:34 PM, Sebastian Andrzej Siewior wrote:
>> Do we really need #3 (and then #4)? Given the complexity we have already, is
>> there any benefit by decreasing this value?
>
> I specifically requested we add ti,charge-delay to the device tree because it
> is THE critical value to tune for a given design. Although I think the
> current value of 0xB000 will be suitable for a great many designs, I expect
> that many users will need to adjust this value for their hardware. Details
> such as which touchscreen vendor is being used and how the touchscreen is
> connected (header vs cable) have an effect on what's appropriate here.
Oh. That is one knob I hoped we could avoid since I haven't seen it
before on other TSCs. But okay. Please make sure that there is a
message printed if the default value is used. And lets hope the user
will do something about his.
>> Would someone want to increase it? Can we safely determine a value which
>> works for everyone?
>
> This value represents a hardware delay before checking for the pen-up event.
> So in the scenario where someone is seeing excessive false pen-up events they
> will want to increase this parameter. The downsize of making this larger is
> that it decreases the overall sampling speed of both the touchscreen as well
> as the standalone ADC samples. At one point I tried making it huge, but that
> made the touchscreen overly sluggish because the sampling became too slow.
> So there is a definite trade-off that if you make it too large the
> touchscreen becomes sluggish, and if you make it too small then you may see
> false pen-up events. The optimal value will need to be tuned for a given
> design.
I applied the patches from this series and did the following test on my
am335x-evm: A mug on the touchscreen (to make sure the events are
coming), evtest on the event node to see that the events and loop of
cat /sys/bus/iio/devices/iio\:device0/in_voltage4_raw
In the past I was able lock up the TSC/ADC HW that way (see commit
7ca6740cd1 ("mfd: input: iio: ti_amm335x: Rework TSC/ADC
synchronization")) for details.
With this patches applied I don't seen any TSC events once the IIO
interface is (heavily) used. Can this be fixed?
Sebastian
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