On Monday 03 November 2014 05:47 PM, Sebastian Andrzej Siewior wrote:
> 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?
I ran following commands
$ evtest /dev/input/touchscreen0 &
(with heavy item on touchscreen)
and
$ cat /sys/bus/iio/devices/iio\:device0/scan_elements/in_voltage4_en
(in a busy loop)
I tried above experiment on my board but I didn't hit any problem even
after running for close to 30 minutes. I was unable to reproduce failure
The problem may be in configuring correct charge-delay value. Please run:
$ ts_test > /dev/null
and let me know if pen events are being detected properly.
>
> Sebastian
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