linux-kernel - Re: [PATCH 1/1] spi: spi-gpio: Add dt support for a single device with no chip select

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Message-ID: <20141027173055.GD4971@leverpostej>
Date:	Mon, 27 Oct 2014 17:30:55 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Torsten Fleischer <torfl6749@...il.com>
Cc:	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/1] spi: spi-gpio: Add dt support for a single device
 with no chip select

On Mon, Oct 27, 2014 at 03:27:17PM +0000, Torsten Fleischer wrote:
> From: Torsten Fleischer <torfl6749@...il.com>
> 
> Use an empty 'cs-gpios' property if a single device is connected which
> has no chip select.
> This refers to the discussion at https://lkml.org/lkml/2013/11/13/62.
> 
> Signed-off-by: Torsten Fleischer <torfl6749@...il.com>
> ---
>  Documentation/devicetree/bindings/spi/spi-gpio.txt |  6 ++++--
>  drivers/spi/spi-gpio.c                             | 10 +++++++---
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/spi/spi-gpio.txt b/Documentation/devicetree/bindings/spi/spi-gpio.txt
> index 8a824be..ad8795f 100644
> --- a/Documentation/devicetree/bindings/spi/spi-gpio.txt
> +++ b/Documentation/devicetree/bindings/spi/spi-gpio.txt
> @@ -8,8 +8,10 @@ Required properties:
>   - gpio-sck: GPIO spec for the SCK line to use
>   - gpio-miso: GPIO spec for the MISO line to use
>   - gpio-mosi: GPIO spec for the MOSI line to use
> - - cs-gpios: GPIOs to use for chipselect lines
> - - num-chipselects: number of chipselect lines
> + - cs-gpios: GPIOs to use for chipselect lines. Leave this property empty if
> +             a single device with no chip select is connected.
> + - num-chipselects: Number of chipselect lines. Has to be "1" even if a single
> +                    device with no chip select is connected.

Why not just have num-chipselectes = <0>, and no cs-gpios property?

That would match the HW, and is unambigious as the author has to state
explicitly that there are no chipselects.

Mark.

>  
>  Example:
>  
> diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c
> index 9f59553..b343818a 100644
> --- a/drivers/spi/spi-gpio.c
> +++ b/drivers/spi/spi-gpio.c
> @@ -461,9 +461,13 @@ static int spi_gpio_probe(struct platform_device *pdev)
>  		 * property of the node.
>  		 */
>  
> -		for (i = 0; i < SPI_N_CHIPSEL; i++)
> -			spi_gpio->cs_gpios[i] =
> -				of_get_named_gpio(np, "cs-gpios", i);
> +		if ((SPI_N_CHIPSEL == 1) &&
> +				(of_gpio_named_count(np, "cs-gpios") == 0))
> +			spi_gpio->cs_gpios[0] = SPI_GPIO_NO_CHIPSELECT;
> +		else
> +			for (i = 0; i < SPI_N_CHIPSEL; i++)
> +				spi_gpio->cs_gpios[i] =
> +					of_get_named_gpio(np, "cs-gpios", i);
>  	}
>  #endif
>  
> -- 
> 1.8.4.5
> 
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