[PATCH 1/4 v5] of_spi: add generic binding support to specify cs gpio

[Grant Likely]

On Fri,  9 Mar 2012 19:25:44 +0100, Jean-Christophe PLAGNIOL-VILLARD <plagnioj at jcrosoft.com> wrote:
> This will allow to use gpio for chip select with no modification in the
> driver binding
> 
> When use the cs-gpios, the gpio number will be passed via the cs_gpio field
> and the number of chip select will automatically increased.
> 
> Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj at jcrosoft.com>
> Cc: devicetree-discuss at lists.ozlabs.org
> Cc: spi-devel-general at lists.sourceforge.net
> ---
> v5:
> 	update grant comment to simplify the cs_gpio management
> 
> Best Regards,
> J.
>  Documentation/devicetree/bindings/spi/spi-bus.txt |    6 ++
>  drivers/spi/spi.c                                 |   55 +++++++++++++++++++-
>  include/linux/spi/spi.h                           |    4 ++
>  3 files changed, 62 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
> index e782add..c253379 100644
> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
> @@ -12,6 +12,7 @@ The SPI master node requires the following properties:
>  - #size-cells     - should be zero.
>  - compatible      - name of SPI bus controller following generic names
>      		recommended practice.
> +- cs-gpios	  - (optional) gpios chip select.
>  No other properties are required in the SPI bus node.  It is assumed
>  that a driver for an SPI bus device will understand that it is an SPI bus.
>  However, the binding does not attempt to define the specific method for
> @@ -21,6 +22,8 @@ assumption that board specific platform code will be used to manage
>  chip selects.  Individual drivers can define additional properties to
>  support describing the chip select layout.
>  
> +If cs-gpios is used the number of chip select will automatically increased.
> +
>  SPI slave nodes must be children of the SPI master node and can
>  contain the following properties.
>  - reg             - (required) chip select address of device.
> @@ -34,6 +37,9 @@ contain the following properties.
>  - spi-cs-high     - (optional) Empty property indicating device requires
>      		chip select active high
>  
> +If a gpio chipselect is used for the SPI slave the gpio number will be passed
> +via the cs_gpio
> +
>  SPI example for an MPC5200 SPI bus:
>  	spi at f00 {
>  		#address-cells = <1>;
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index b2ccdea..446eee5 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -28,6 +28,7 @@
>  #include <linux/mod_devicetable.h>
>  #include <linux/spi/spi.h>
>  #include <linux/of_spi.h>
> +#include <linux/of_gpio.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/export.h>
>  
> @@ -322,6 +323,7 @@ struct spi_device *spi_alloc_device(struct spi_master *master)
>  	spi->dev.parent = &master->dev;
>  	spi->dev.bus = &spi_bus_type;
>  	spi->dev.release = spidev_release;
> +	spi->cs_gpio = -EINVAL;
>  	device_initialize(&spi->dev);
>  	return spi;
>  }
> @@ -339,15 +341,16 @@ EXPORT_SYMBOL_GPL(spi_alloc_device);
>  int spi_add_device(struct spi_device *spi)
>  {
>  	static DEFINE_MUTEX(spi_add_lock);
> -	struct device *dev = spi->master->dev.parent;
> +	struct spi_master *master = spi->master;
> +	struct device *dev = master->dev.parent;
>  	struct device *d;
>  	int status;
>  
>  	/* Chipselects are numbered 0..max; validate. */
> -	if (spi->chip_select >= spi->master->num_chipselect) {
> +	if (spi->chip_select >= master->num_chipselect) {
>  		dev_err(dev, "cs%d >= max %d\n",
>  			spi->chip_select,
> -			spi->master->num_chipselect);
> +			master->num_chipselect);
>  		return -EINVAL;
>  	}
>  
> @@ -371,6 +374,9 @@ int spi_add_device(struct spi_device *spi)
>  		goto done;
>  	}
>  
> +	if (master->cs_gpios)
> +		spi->cs_gpio = master->cs_gpios[spi->chip_select];
> +

I still don't understand the need for this.  Only the master driver will need
this data, and it is already stored in the master->cs_gpios array.  Why
does it need to get duplicated into the spi_device?

>  	/* Drivers may modify this initial i/o setup, but will
>  	 * normally rely on the device being setup.  Devices
>  	 * using SPI_CS_HIGH can't coexist well otherwise...
> @@ -561,6 +567,45 @@ struct spi_master *spi_alloc_master(struct device *dev, unsigned size)
>  }
>  EXPORT_SYMBOL_GPL(spi_alloc_master);
>  
> +#ifdef CONFIG_OF
> +static int of_spi_register_master(struct spi_master *master)
> +{
> +	int nb, i;
> +	int *cs;
> +	struct device_node *np = master->dev.of_node;
> +
> +	if (!np)
> +		return 0;
> +
> +	nb = of_gpio_named_count(np, "cs-gpios");
> +
> +	if (nb < 1)
> +		return 0;
> +
> +	cs = devm_kzalloc(&master->dev,
> +			  sizeof(int) * (master->num_chipselect + nb),
> +			  GFP_KERNEL);

sizeof(*cs)

> +	master->cs_gpios = cs;
> +
> +	if (!master->cs_gpios)
> +		return -ENOMEM;
> +
> +	memset(cs, -EINVAL, master->num_chipselect);
> +	master->num_chipselect += nb;

Looks buggy.  Should be:
	if (nb > master->num_chipselect)
		master->num_chipselect = nb;

However, this is actually quite risky.  Changing the size of
num_chipselect without the driver knowing about it will most likely
cause breakage in drivers.  Drivers may use it as an array index, and
if it gets increased then there will be problems.  In fact, drivers
are probably using spi->chip_select as an array or register index so I
don't think it can be transparently extended to include gpios.

So, this function must change.  It cannot be called automatically
from spi_register_master().  It needs to be a library function that spi bus
drivers must call explicitly so they are prepared for a change in the
num_chipselect value.

Also, if we're doing this, then the gpio cs manipulation hook should be
moved out of spi_bitbang and into the core spi_master.  There should
also be a stock function for manipulating gpio chip selects. I don't want
spi driver authors under the impression that they should open code the
chip select manipulation.

> +	cs += master->num_chipselect;
> +
> +	for (i = 0; i < nb; i++)
> +		cs[i] = of_get_named_gpio(np, "cs-gpios", i);
> +
> +	return 0;
> +}
> +#else
> +static int of_spi_register_master(struct spi_master *master)
> +{
> +	return 0;
> +}
> +#endif
> +
>  /**
>   * spi_register_master - register SPI master controller
>   * @master: initialized master, originally from spi_alloc_master()
> @@ -592,6 +637,10 @@ int spi_register_master(struct spi_master *master)
>  	if (!dev)
>  		return -ENODEV;
>  
> +	status = of_spi_register_master(master);
> +	if (status)
> +		return status;
> +
>  	/* even if it's just one always-selected device, there must
>  	 * be at least one chipselect
>  	 */
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index 176fce9..328d492 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -89,6 +89,7 @@ struct spi_device {
>  	void			*controller_state;
>  	void			*controller_data;
>  	char			modalias[SPI_NAME_SIZE];
> +	int			cs_gpio;	/* chip select gpio */
>  
>  	/*
>  	 * likely need more hooks for more protocol options affecting how
> @@ -318,6 +319,9 @@ struct spi_master {
>  
>  	/* called on release() to free memory provided by spi_master */
>  	void			(*cleanup)(struct spi_device *spi);
> +
> +	/* gpio chip select */
> +	int			*cs_gpios;
>  };
>  
>  static inline void *spi_master_get_devdata(struct spi_master *master)
> -- 
> 1.7.7
> 
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-- 
Grant Likely, B.Sc, P.Eng.
Secret Lab Technologies,Ltd.