linux-kernel - Re: [PATCH] sh: maple: add support for Maple controller as a joystick

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Message-Id: <1229806020.6502.35.camel@localhost.localdomain>
Date:	Sat, 20 Dec 2008 20:47:00 +0000
From:	Adrian McMenamin <adrian@...golddream.dyndns.info>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Matt Fleming <matt@...sole-pimps.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-sh <linux-sh@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH] sh: maple: add support for Maple controller as a
 joystick

On Sat, 2008-12-20 at 12:19 -0800, Dmitry Torokhov wrote:
> On Saturday 20 December 2008 08:07:27 Adrian McMenamin wrote:
> > On Sat, 2008-12-20 at 15:16 +0000, Matt Fleming wrote:
> > > On Fri, Dec 19, 2008 at 11:15:42PM +0000, Adrian McMenamin wrote:
> > > > Add support for the SEGA Dreamcast Maple controller as a joystick
> > >
> > > [snip]
> > >
> > > > +	struct dc_pad *pad = maple_get_drvdata(mapledev);
> > > > +	struct input_dev *dev = pad->dev;
> > > > +	unsigned char *res = mq->recvbuf;
> > > > +
> > > > +	buttons = ~cpu_to_le16(*(unsigned short *)(res + 8));
> > > > +
> > >
> > > I may be wrong but shouldn't this use the I/O accessor functions?
> >
> > It's not iomemory, so I don't think so. The maple bus writes to a buffer
> > in the physical RAM.
> >
> 
> Hmm, but why we are going _from_ cpu order to le16??? I'd expect we
> wanted to do conversion the other way around. I pulled it out of 'next'
> for now.
> 
The data is transmitted here by the bus in 32 bit little endian blocks
but makes sense in le16 bit lumps. Off is 1 and on is 0 - hence the ~

The first 16 bits are the button data the next 16 bits are the (start
of) the axis data. Both cpu and bus data (in this case - it can vary)
are little endian.


        

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