linux-kernel - Re: [PATCH v2 3/3] can: sja1000: of: add compatibility with Technologic Systems version

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Date:	Tue, 12 Jan 2016 10:51:15 -0500
From:	Damien Riegel <damien.riegel@...oirfairelinux.com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-can@...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>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	kernel@...oirfairelinux.com
Subject: Re: [PATCH v2 3/3] can: sja1000: of: add compatibility with
 Technologic Systems version

On Tue, Jan 12, 2016 at 08:55:38AM +0100, Marc Kleine-Budde wrote:
> On 12/24/2015 06:42 PM, Damien Riegel wrote:
> > Technologic Systems provides an IP compatible with the SJA1000,
> > instantiated in an FPGA. Because of some bus widths issue, access to
> > registers is made through a "window" that works like this:
> > 
> >     base + 0x0: address to read/write
> >     base + 0x2: 8-bit register value
> 
> Why do you use io{read,write}16 if it's a 8 bit register?

8-bit is at the IP level, but the bus between the SoC and the FPGA only
supports 16-bit wide access. The point of the window is to convert
between 16-bit and 8-bit access.

Damien