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>

1 files changed, 3 insertions, 0 deletions

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)