linux-kernel - Re: [PATCH] staging/comedi: Fix undefined array subscript

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Message-ID: <511B995E.3030905@mev.co.uk>
Date:	Wed, 13 Feb 2013 13:47:10 +0000
From:	Ian Abbott <abbotti@....co.uk>
To:	Ian Abbott <ian.abbott@....co.uk>
CC:	Dan Carpenter <dan.carpenter@...cle.com>,
	Peter Huewe <peterhuewe@....de>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	Mori Hess <fmhess@...rs.sourceforge.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging/comedi: Fix undefined array subscript

On 2013-02-13 11:56, Ian Abbott wrote:
> For a digital output subdevice, you could either read back the current
> values directly from the hardware or just use the value previously
> written.  The Velleman K8055 doesn't have a command to read back the
> digital outputs from the hardware, so the last written value has to be
> used.  But what if the digital outputs have never been written (or the
> analog outputs have never been written, since the same command updates
> all analog and digital channels)?  A "reset" command is sent to the
> hardware on initialization by vmk80xx_reset_device() (only called for
> the K8055), but I don't know what effect this has on the actual digital
> (and analog) outputs (though I could find out easily enough as we appear
> to have one of these kits (assembled) lying around in the office).  If
> necessary, we may have to also send a "write" command on initialization
> to make the hardware outputs match the initial software state.

I've had a quick play with a K8055 and it seems the "reset" command 
issued during hardware initialization has no effect on the digital 
outputs.  (I tested this by setting some digital outputs with comedi 
instructions - there are some handy LEDs on the board that light up or 
not according to the state of the digital outputs - then rmmod'ing and 
modprobe'ing the vmk80xx module - the LEDs remained in the same state.)

Since we can't read back the outputs on this board we should initialize 
them to a known state.  I'll submit some patches later.

Nothing to do with the patch in this thread, which has my Ack.

Acked-by: Ian Abbott <abbotti@....co.uk>

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-
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