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

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Date:	Mon, 3 Nov 2014 19:09:21 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	Vignesh R <vigneshr@...com>
Cc:	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@...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

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?

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)

> 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?

Thanks,
Richard
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