Re: [PATCH 1/4 v4] of_spi: add generic binding support to specify cs gpio

On Wed,  7 Mar 2012 13:23:06 +0100, Jean-Christophe PLAGNIOL-VILLARD [off-list ref] wrote:

spi->cs_gpio isn't used anywhere.

I think this can be simplified.  Rather than trying to optimize by having
a set of integrated cs lines followed by a gpio set, I think it would be
better to have a single cs_gpios table that covers the whole range of
num_chipselect; even if they overlap natural cs lines.  That will make for
an easier to use binding since users won't need to remember how many natural
cs lines are on the device when filling the cs-gpios property.  It will
also make the code simpler because first_gpio_cs and num_gpio_cs can both
be eliminated.  It also means the core can have exact knowledge about which
gpio is associated with which cs number.

-- 
Grant Likely, B.Sc, P.Eng.
Secret Lab Technologies,Ltd.

On 08:14 Fri 09 Mar     , Grant Likely wrote:

On Wed,  7 Mar 2012 13:23:06 +0100, Jean-Christophe PLAGNIOL-VILLARD [off-list ref] wrote:

quoted

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 <redacted>
Cc: devicetree-discuss at lists.ozlabs.org
Cc: spi-devel-general at lists.sourceforge.net
---
v4:
	use cs_gpio to pass the gpio number

Best Regards,
J.
 Documentation/devicetree/bindings/spi/spi-bus.txt |    6 ++
 drivers/spi/spi.c                                 |   57 +++++++++++++++++++-
 include/linux/spi/spi.h                           |    6 ++
 3 files changed, 66 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 controller_data
+
 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..c1d0955 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 +374,13 @@ int spi_add_device(struct spi_device *spi)
 		goto done;
 	}
 
+	if (master->num_gpio_cs &&
+	    spi->chip_select >= master->first_gpio_cs) {
+		int num = spi->chip_select - master->first_gpio_cs;
+
+		spi->cs_gpio = master->cs_gpios[num];

spi->cs_gpio isn't used anywhere.

driver
as example atmel spi

I choose to let the driver to manage it as they may need to manange specific
register when using both hw and gpio cs

quoted

+	}
+
 	/* 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 +571,43 @@ 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) * nb, GFP_KERNEL);
+	master->cs_gpios = cs;
+
+	if (!master->cs_gpios)
+		return -ENOMEM;
+
+	master->first_gpio_cs = master->num_chipselect;
+	master->num_chipselect += nb;
+	master->num_gpio_cs = nb;

I think this can be simplified.  Rather than trying to optimize by having
a set of integrated cs lines followed by a gpio set, I think it would be
better to have a single cs_gpios table that covers the whole range of
num_chipselect; even if they overlap natural cs lines.  That will make for
an easier to use binding since users won't need to remember how many natural
cs lines are on the device when filling the cs-gpios property.  It will
also make the code simpler because first_gpio_cs and num_gpio_cs can both
be eliminated.  It also means the core can have exact knowledge about which
gpio is associated with which cs number.

ok why not so I feel the array with -EINVAL for hw cs;

Best Regards,
J.