linux-kernel - Re: [PATCH 2/2] Input: add touchscreen support for TS-4800

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Date:	Sun, 13 Dec 2015 15:55:57 -0500
From:	Damien Riegel <damien.riegel@...oirfairelinux.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
	devicetree@...r.kernel.org, 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>, kernel@...oirfairelinux.com
Subject: Re: [PATCH 2/2] Input: add touchscreen support for TS-4800

Hi Dmitry

On Sat, Dec 12, 2015 at 08:58:58PM -0800, Dmitry Torokhov wrote:
> Hi Damien,
> 
> On Thu, Dec 10, 2015 at 11:11:12AM -0500, Damien Riegel wrote:
> > On this board, the touchscreen, an ads7843, is not handled directly by
> > Linux but by a companion FPGA. This FPGA is memory-mapped and the IP
> > design is very similar to the mk712.
> 
> ...
> 
> > +
> > +	poll_dev = devm_input_allocate_polled_device(&pdev->dev);
> > +	if (!poll_dev)
> > +		return -ENOMEM;
> 
> I wonder how useful touchscreen implemented as polling device is. Isn't
> there an interrupt line for it?
 
There is an interrupt line between the touchscreen and the FGPA, but not
between the FPGA and the SoC. I agree it is a bit peculiar. Hopefully on
more recent boards, they changed their design to handle the touchscreen
directly with Linux.

Thanks,
Damien

> Thanks.
> 
> -- 
> Dmitry
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