linux-kernel - Re: [PATCH 0/4] Touchscreen performance related fixes

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Date:	Mon, 17 Nov 2014 17:09:45 +0530
From:	Vignesh R <vigneshr@...com>
To:	Johannes Pointner <johannes.pointner@...il.com>
CC:	Richard Cochran <richardcochran@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Benoit Cousson <bcousson@...libre.com>,
	Tony Lindgren <tony@...mide.com>,
	Russell King <linux@....linux.org.uk>,
	Jonathan Cameron <jic23@...nel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	<devicetree@...r.kernel.org>, Lars-Peter Clausen <lars@...afoo.de>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Jan Kardell <jan.kardell@...liq.com>,
	linux-iio <linux-iio@...r.kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	<linux-input@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Meerwald <pmeerw@...erw.net>,
	Hartmut Knaack <knaack.h@....de>, <linux-omap@...r.kernel.org>,
	Lee Jones <lee.jones@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Brad Griffis <bgriffis@...com>
Subject: Re: [PATCH 0/4] Touchscreen performance related fixes

Hi,

On Thursday 13 November 2014 05:53 PM, Vignesh R wrote:
> Hi,
> 
> On Wednesday 12 November 2014 06:30 PM, Johannes Pointner wrote:
>> Hello Vignesh,
>>
>> I tried your patch version 3 on a customized board and had some
>> behavior I couldn't explain.
>> If I only use the touchscreen it works fine but if I also read values
>> from the ADCs then I get a lot of pen_up events even if I am still
>> touching the screen.
>> For the test I read via
>> # cat /sys/bus/iio/devices/iio\:device0/in_voltage5_raw
>> values from the ADC in an busy loop as you explained in an email
>> before. Did you also experience such behavior or do you know what
>> causes it?
> 
> Thanks for testing. I was able to fix this issue. Will post version 4
> shortly.
> 

Were you able to test the v4 patch series on your board? Is the issue fixed?

> Regards
> Vignesh
> 
>>
>> Without the patches the touchscreen works fine during the iio test.
>>
>> Thanks,
>> Hannes
>>
>> 2014-11-06 8:42 GMT+01:00 Vignesh R <vigneshr@...com>:
>>>
>>>
>>> On Monday 03 November 2014 11:39 PM, Richard Cochran wrote:
>>>> On Mon, Oct 27, 2014 at 04:38:27PM +0530, Vignesh R wrote:
>>>>> This series of patches fix TSC defects related to lag in touchscreen
>>>>> performance and cursor jump at touch release. The lag was result of
>>>>> udelay in TSC interrupt handler. Cursor jump due to false pen-up event.
>>>>> The patches implement Advisory 1.0.31 in silicon errata of am335x-evm
>>>>> to avoid false pen-up events and remove udelay.
>>>>
>>>> That advisory has two workarounds. You have chosen the second one?
>>>
>>> Work around one. Hence 5 wire design is not broken.
>>>
>>>>
>>>> The text of the second workaround says it only works on 4 wire setups,
>>>> so I wonder how 5 wire designs will be affected.
>>>>
>>>>> The advisory says to use
>>>>> steps 1 to 4 for ADC and 5 to 16 for TSC (assuming 4 wire TSC and 4 channel
>>>>> ADC).
>>>>
>>>> No, it doesn't say that. (sprz360f.pdf)
>>>
>>> The pen up event detection happens immediately after charge step. Hence,
>>> interchanging ADC and TSC steps makes sure that sampling of touch
>>> co-ordinates and pen events are done one after the other. This
>>> workaround was suggested by internal hardware folks. Earlier ADC steps
>>> intervened between sampling of co-ordinates and pen event detection
>>> which is not desirable.
>>>
>>>>
>>>>> Further the X co-ordinate must be the last one to be sampled just
>>>>> before charge step. The first two patches implement the required changes.
>>>>
>>>> FWIW, I implemented the first workaround and removed the udelay not
>>>> too long ago. Like Sebastian, I saw the TSC unit hang after about
>>>> 50000 interrupts when running with the workaround.
>>>>
>>>> Did you test you patch for very long?
>>>
>>> Yes, I tested for about 200000 interrupts and I didn't see any hang.
>>> This patch series does not just implement workaround but also does some
>>> minor changes, such as interchanging ADC and TSC steps etc, which makes
>>> TSC driver more robust. Let me know if you encounter any issues with my
>>> patch series.
>>>
>>> Regards
>>> Vignesh
>>>
>>>>
>>>> Thanks,
>>>> Richard
>>>>
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