[U-Boot] [PATCH 3/9] i.MX31: support GPIO as a chip-select in the mxc_spi driver

[Jean-Christophe PLAGNIOL-VILLARD]

On 17:59 Wed 04 Feb     , Guennadi Liakhovetski wrote:
> Some SPI devices have special requirements on chip-select handling.
> With this patch we can use a GPIO as a chip-select and strictly follow
> the SPI_XFER_BEGIN and SPI_XFER_END flags.
> 
> Signed-off-by: Guennadi Liakhovetski <lg at denx.de>
> ---
> 
> Jean-Christophe: one more for you to ack.
> 
>  drivers/spi/mxc_spi.c |   35 +++++++++++++++++++++++++++++------
>  1 files changed, 29 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/spi/mxc_spi.c b/drivers/spi/mxc_spi.c
> index 9267341..eacd36c 100644
> --- a/drivers/spi/mxc_spi.c
> +++ b/drivers/spi/mxc_spi.c
> @@ -32,6 +32,8 @@
>  
>  #else
>  
> +#include <asm/arch/mx31.h>
> +
>  #define MXC_CSPIRXDATA		0x00
>  #define MXC_CSPITXDATA		0x04
>  #define MXC_CSPICTRL		0x08
> @@ -68,6 +70,7 @@ struct mxc_spi_slave {
>  	struct spi_slave slave;
>  	unsigned long	base;
>  	u32		ctrl_reg;
> +	int		gpio;
>  };
>  
>  static inline struct mxc_spi_slave *to_mxc_spi_slave(struct spi_slave *slave)
> @@ -91,6 +94,9 @@ static u32 spi_xchg_single(struct spi_slave *slave, u32 data,
>  	struct mxc_spi_slave *mxcs = to_mxc_spi_slave(slave);
>  	unsigned int cfg_reg = reg_read(mxcs->base + MXC_CSPICTRL);
>  
> +	if (mxcs->gpio > 0 && (flags & SPI_XFER_BEGIN))
> +		mx31_gpio_set(mxcs->gpio, !!(mxcs->ctrl_reg & MXC_CSPICTRL_SSPOL));
> +
>  	reg_write(mxcs->base + MXC_CSPITXDATA, data);
>  
>  	cfg_reg |= MXC_CSPICTRL_XCH;
> @@ -100,6 +106,9 @@ static u32 spi_xchg_single(struct spi_slave *slave, u32 data,
>  	while (reg_read(mxcs->base + MXC_CSPICTRL) & MXC_CSPICTRL_XCH)
>  		;
>  
> +	if (mxcs->gpio > 0 && (flags & SPI_XFER_END))
> +		mx31_gpio_set(mxcs->gpio, !(mxcs->ctrl_reg & MXC_CSPICTRL_SSPOL));
> +
>  	return reg_read(mxcs->base + MXC_CSPIRXDATA);
>  }
>  
> @@ -175,10 +184,28 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
>  	unsigned int ctrl_reg;
>  	struct mxc_spi_slave *mxcs;
>  
> -	if (bus >= sizeof(spi_bases) / sizeof(spi_bases[0]) ||
> -	    cs > 3)
> +	if (bus >= sizeof(spi_bases) / sizeof(spi_bases[0]))
> +		return NULL;
> +
> +	mxcs = malloc(sizeof(struct mxc_spi_slave));
> +	if (!mxcs)
>  		return NULL;
>  
> +	/*
> +	 * Some SPI devices require active chip-select over multiple
> +	 * transactions, we achieve this using a GPIO. Still, the SPI
> +	 * controller has to be configured to use one of its own chipselects.
> +	 * To use this feature you have to call spi_setup_slave() with
> +	 * cs = internal_cs | (gpio << 8), and you have to use some unused
> +	 * on this SPI controller cs between 0 and 3.
> +	 */
> +	if (cs > 3) {
> +		mxcs->gpio = cs >> 8;
> +		cs &= 3;
> +		mx31_gpio_direction(mxcs->gpio, MX31_GPIO_DIRECTION_OUT);
> +	} else
> +		mxcs->gpio = -1;
> +
why not add a callback for the chipselect instead
as example if you have to use a gpio extender it will simplest to implent
instead of hack the SPI driver

Best Regars,
J.