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

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Message-ID: <20171115153940.cxlacbcyl3jxiwex@sirena.org.uk>
Date:   Wed, 15 Nov 2017 15:39:40 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Jan Glauber <jan.glauber@...iumnetworks.com>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        Tim Harvey <tharvey@...eworks.com>, linux-spi@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can <linux-can@...r.kernel.org>
Subject: Re: MCP251x SPI CAN controller on Cavium ThunderX

On Wed, Nov 15, 2017 at 01:07:54PM +0100, Jan Glauber wrote:

> To support this full duplex transfer the Cavium SPI controller needs
> to know the receive lenght before setting up the transaction.

> spi_transfer only includes the total length, so I don't see how this
> should work.

For a full duplex transfer the recieve length *is* the total length of
the transfer.  If there is a mix of tx, rx and full duplex then you need
multiple xfers in the transfer.

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