of_spi: add generic binding support to specify cs gpio

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 with max(hw cs, gpio cs).

So if for example the controller has 2 CS lines, and the cs-gpios
property looks like this:

cs-gpios = <&gpio1 0 0> <0> <&gpio1 1 0> <&gpio1 2 0>;

Then it should be configured so that num_chipselect = 4 with the
following mapping:

cs0 : &gpio1 0 0
cs1 : native
cs2 : &gpio1 1 0
cs3 : &gpio1 2 0

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: devicetree-discuss@lists.ozlabs.org
Cc: spi-devel-general@lists.sourceforge.net
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
[grant.likely: fixed up type of cs count so min() can do type checking]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

3 files changed, 74 insertions, 3 deletions

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index d2c33d0f533e..77a8b0d39b54 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
@@ -24,6 +25,22 @@ support describing the chip select layout.
 Optional property:
 - num-cs : total number of chipselects
 
+If cs-gpios is used the number of chip select will automatically increased
+with max(cs-gpios > hw cs)
+
+So if for example the controller has 2 CS lines, and the cs-gpios
+property looks like this:
+
+cs-gpios = <&gpio1 0 0> <0> <&gpio1 1 0> <&gpio1 2 0>;
+
+Then it should be configured so that num_chipselect = 4 with the
+following mapping:
+
+cs0 : &gpio1 0 0
+cs1 : native
+cs2 : &gpio1 1 0
+cs3 : &gpio1 2 0
+
 SPI slave nodes must be children of the SPI master node and can
 contain the following properties.
 - reg             - (required) chip select address of device.
@@ -37,6 +54,9 @@ 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@f00 {
                 #address-cells = <1>;
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 84c2861d6f4d..1587a4a5ff41 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -30,6 +30,7 @@
 #include <linux/slab.h>
 #include <linux/mod_devicetable.h>
 #include <linux/spi/spi.h>
+#include <linux/of_gpio.h>
 #include <linux/pm_runtime.h>
 #include <linux/export.h>
 #include <linux/sched.h>
@@ -327,6 +328,7 @@ 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;
 }
@@ -344,15 +346,16 @@ 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;
         }
 
@@ -376,6 +379,9 @@ int spi_add_device(struct spi_device *spi)
                 goto done;
         }
 
+        if (master->cs_gpios)
+                spi->cs_gpio = master->cs_gpios[spi->chip_select];
+
         /* 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...
@@ -946,6 +952,44 @@ 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)
+{
+        u16 nb;
+        int i, *cs;
+        struct device_node *np = master->dev.of_node;
+
+        if (!np)
+                return 0;
+
+        nb = of_gpio_named_count(np, "cs-gpios");
+        master->num_chipselect = max(nb, master->num_chipselect);
+
+        if (nb < 1)
+                return 0;
+
+        cs = devm_kzalloc(&master->dev,
+                          sizeof(int) * master->num_chipselect,
+                          GFP_KERNEL);
+        master->cs_gpios = cs;
+
+        if (!master->cs_gpios)
+                return -ENOMEM;
+
+        memset(cs, -EINVAL, 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()
@@ -977,6 +1021,10 @@ 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 fa702aeb5038..f62918946d86 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -90,6 +90,7 @@ 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
@@ -362,6 +363,8 @@ struct spi_master {
         int (*transfer_one_message)(struct spi_master *master,
                                     struct spi_message *mesg);
         int (*unprepare_transfer_hardware)(struct spi_master *master);
+        /* gpio chip select */
+        int                     *cs_gpios;
 };
 
 static inline void *spi_master_get_devdata(struct spi_master *master)