linux-kernel - Re: MCP251x SPI CAN controller on Cavium ThunderX

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Message-ID: <20171116124154.allayndu467osija@sirena.org.uk>
Date:   Thu, 16 Nov 2017 12:41:54 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     David Daney <ddaney@...iumnetworks.com>,
        Jan Glauber <jan.glauber@...iumnetworks.com>,
        linux-spi@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: Re: MCP251x SPI CAN controller on Cavium ThunderX

On Wed, Nov 15, 2017 at 03:18:59PM -0800, Tim Harvey wrote:

> I could re-write the mcp251x driver to not use full-duplex but I'm
> assuming most SPI drivers use full-duplex transactions.

I'd not actually say that's the case - the bulk of devices do some kind
of command/response or register/value thing, full duplex is moderately
complex to work with and ends up needing a constant data stream between
the two devices.  It does happen (and some controllers always transfer
data in both directions) but most of the time only one direction has any
meaning.

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