linux-kernel - Re: [PATCH] can: mcp251x: convert to half-duplex SPI

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Message-ID: <0ac77abd-0df5-e437-ea46-f6c77f59b81c@pengutronix.de>
Date:   Tue, 25 Feb 2020 22:43:07 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Tim Harvey <tharvey@...eworks.com>, linux-kernel@...r.kernel.org,
        linux-can@...r.kernel.org, Wolfgang Grandegger <wg@...ndegger.com>
Cc:     Timo Schlüßler <schluessler@...use.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH] can: mcp251x: convert to half-duplex SPI

On 2/25/20 7:35 PM, Tim Harvey wrote:
> Some SPI host controllers such as the Cavium Thunder do not support
> full-duplex SPI. Using half-duplex transfers allows the driver to work
> with those host controllers.

There are several transfers left in the driver, where both rx_buf and
tx_buf are set. How does your host controller driver know which one to
handle?

Marc

> Signed-off-by: Tim Harvey <tharvey@...eworks.com>
> ---
>  drivers/net/can/spi/mcp251x.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/can/spi/mcp251x.c b/drivers/net/can/spi/mcp251x.c
> index 5009ff2..840c31c 100644
> --- a/drivers/net/can/spi/mcp251x.c
> +++ b/drivers/net/can/spi/mcp251x.c
> @@ -290,23 +290,23 @@ static u8 mcp251x_read_reg(struct spi_device *spi, u8 reg)
>  	priv->spi_tx_buf[0] = INSTRUCTION_READ;
>  	priv->spi_tx_buf[1] = reg;
>  
> -	mcp251x_spi_trans(spi, 3);
> -	val = priv->spi_rx_buf[2];
> +	spi_write_then_read(spi, priv->spi_tx_buf, 2, &val, 1);
>  
>  	return val;
>  }
>  
>  static void mcp251x_read_2regs(struct spi_device *spi, u8 reg, u8 *v1, u8 *v2)
>  {
> +	u8 val[4] = {0};
>  	struct mcp251x_priv *priv = spi_get_drvdata(spi);
>  
>  	priv->spi_tx_buf[0] = INSTRUCTION_READ;
>  	priv->spi_tx_buf[1] = reg;
>  
> -	mcp251x_spi_trans(spi, 4);
> +	spi_write_then_read(spi, priv->spi_tx_buf, 2, val, 2);
>  
> -	*v1 = priv->spi_rx_buf[2];
> -	*v2 = priv->spi_rx_buf[3];
> +	*v1 = val[0];
> +	*v2 = val[1];
>  }
>  
>  static void mcp251x_write_reg(struct spi_device *spi, u8 reg, u8 val)
> 

Marc

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