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Subject: Re: [PATCH] can: mcp251x: convert to half-duplex SPI
From:   Marc Kleine-Budde <mkl@pengutronix.de>
To:     Tim Harvey <tharvey@gateworks.com>
Cc:     open list <linux-kernel@vger.kernel.org>,
        linux-can@vger.kernel.org, Wolfgang Grandegger <wg@grandegger.com>,
        =?UTF-8?Q?Timo_Schl=c3=bc=c3=9fler?= <schluessler@krause.de>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
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Message-ID: <7b85e098-b9a9-dd14-203f-100cdf2e703e@pengutronix.de>
Date:   Wed, 26 Feb 2020 11:19:26 +0100
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On 2/26/20 8:37 AM, Marc Kleine-Budde wrote:
>> Your right... there is the mcp251x_hw_rx_frame() call that also uses
>> spi_rx_buf after a synchronous transfer (I didn't see any others).
>> I'll look at this again.
> 
> Have you hardware to test your changes? I think the SPI framework would
> return an -EINVAL in that case....though the return value is sometimes
> not checked by the driver :/

See https://elixir.bootlin.com/linux/v5.5.6/source/drivers/spi/spi.c#L3413

If you have really have HW with SPI_CONTROLLER_HALF_DUPLEX (a.k.a
SPI_MASTER_HALF_DUPLEX) restrictions, you need to convert _every_
mcp251x_spi_trans() call in the driver, as _always_ both rx_buf _and_
tx_buf are used.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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