linux-kernel - RE: [PATCH 09/20] Input: atmel_mxt_ts - do not read extra (checksum) byte

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Date:	Thu, 22 Mar 2012 10:18:20 -0000
From:	"Bowens, Alan" <Alan.Bowens@...el.com>
To:	"Nick Dyer" <nick.dyer@...ev.co.uk>,
	"Daniel Kurtz" <djkurtz@...omium.org>
Cc:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>,
	"Joonyoung Shim" <jy0922.shim@...sung.com>,
	"Valkonen, Iiro" <iiro.valkonen@...el.com>,
	"Henrik Rydberg" <rydberg@...omail.se>,
	<linux-input@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	"Benson Leung" <bleung@...omium.org>,
	"Yufeng Shen" <miletus@...omium.org>,
	"Tiwari, Atul" <Atul.Tiwari@...el.com>
Subject: RE: [PATCH 09/20] Input: atmel_mxt_ts - do not read extra (checksum) byte

Just to confuse things, the checksum byte is available from the chip if
required. Reading it involves a slightly different approach to normal
message processor reads, in that the host needs to write the 16-bit
address of the message processor, with the MSB set. It must then follow
these two bytes with another byte consisting of the checksum of the
previous two bytes.

This functionality was added at a customer's request, although I don't
know if any current customers actually use it.

Alan Bowens
Section Manager / Atmel Corporation
Tel: (+44) (0)1489-553-611
alan.bowens@...el.com / www.atmel.com

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-----Original Message-----
From: Nick Dyer [mailto:nick.dyer@...ev.co.uk] 
Sent: 20 March 2012 15:08
To: Daniel Kurtz
Cc: Dmitry Torokhov; Joonyoung Shim; Valkonen, Iiro; Henrik Rydberg;
linux-input@...r.kernel.org; linux-kernel@...r.kernel.org; Benson Leung;
Yufeng Shen; Tiwari, Atul; Bowens, Alan
Subject: Re: [PATCH 09/20] Input: atmel_mxt_ts - do not read extra
(checksum) byte

Daniel Kurtz wrote:
> It isn't sent, nor checked anyway, so don't bother reading it.
> 
> Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>

This is fair enough, although IMO the checksum should be checked.

--
Nick Dyer
Software Engineer, ITDev Ltd
Hardware and Software Development Consultancy
Website: http://www.itdev.co.uk
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