linux-kernel - Re: [PATCH] [drivers] [SPI] SPI_GPIO: add support for controllers with missing MISO pin

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Message-ID: <20090507123157.GU32548@trinity.fluff.org>
Date:	Thu, 7 May 2009 13:31:57 +0100
From:	Ben Dooks <ben-linux@...ff.org>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.arm.linux.org.uk" 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	"kyungmin.park@...sung.com" <kyungmin.park@...sung.com>
Subject: Re: [PATCH] [drivers] [SPI] SPI_GPIO: add support for controllers with missing MISO pin

On Thu, May 07, 2009 at 02:24:11PM +0200, Marek Szyprowski wrote:
> There are some boards that do not strictly follow SPI standard and use only 3 wires (SCLK, MOSI, SS) for connecting some simple auxiliary chips and controls them with GPIO based 'spi controller'. In this configuration the MISO line is missing (it is not required if the chip does not transfer any data back to host). The example of such board is a NCP ARM S3C64XX based machine. This patch adds support for such non-standard configuration in GPIO-based SPI controller.

Please wrap your descriptions to 77 or less characters per line.

> Reviewed-by: Kyungmin Park <kyungmin.park@...sung.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> 
> --- 
> 
> diff --git a/drivers/spi/spi_gpio.c b/drivers/spi/spi_gpio.c
> index 26bd03e..5b75601 100644
> --- a/drivers/spi/spi_gpio.c
> +++ b/drivers/spi/spi_gpio.c
> @@ -114,7 +114,10 @@ static inline void setmosi(const struct spi_device *spi, int is_on)
>  
>  static inline int getmiso(const struct spi_device *spi)
>  {
> -	return !!gpio_get_value(SPI_MISO_GPIO);
> +	if (SPI_MISO_GPIO)
> +		return !!gpio_get_value(SPI_MISO_GPIO);
> +	else
> +		return 0;
>  }

Is zero a good approximation for 'no gpio' ?

>  #undef pdata
> @@ -243,9 +246,11 @@ spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label)
>  	if (value)
>  		goto done;
>  
> -	value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
> -	if (value)
> -		goto free_mosi;
> +	if (SPI_MISO_GPIO) {
> +		value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
> +		if (value)
> +			goto free_mosi;
> +	}
>  
>  	value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
>  	if (value)
> @@ -254,7 +259,8 @@ spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label)
>  	goto done;
>  
>  free_miso:
> -	gpio_free(SPI_MISO_GPIO);
> +	if (SPI_MISO_GPIO)
> +		gpio_free(SPI_MISO_GPIO);
>  free_mosi:
>  	gpio_free(SPI_MOSI_GPIO);
>  done:
> @@ -308,7 +314,8 @@ static int __init spi_gpio_probe(struct platform_device *pdev)
>  	if (status < 0) {
>  		spi_master_put(spi_gpio->bitbang.master);
>  gpio_free:
> -		gpio_free(SPI_MISO_GPIO);
> +		if (SPI_MISO_GPIO)
> +			gpio_free(SPI_MISO_GPIO);
>  		gpio_free(SPI_MOSI_GPIO);
>  		gpio_free(SPI_SCK_GPIO);
>  		spi_master_put(master);
> @@ -332,7 +339,8 @@ static int __exit spi_gpio_remove(struct platform_device *pdev)
>  
>  	platform_set_drvdata(pdev, NULL);
>  
> -	gpio_free(SPI_MISO_GPIO);
> +	if (SPI_MISO_GPIO)
> +		gpio_free(SPI_MISO_GPIO);
>  	gpio_free(SPI_MOSI_GPIO);
>  	gpio_free(SPI_SCK_GPIO);
> 
> 
> -------------------------------------------------------------------
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-- 
-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.

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