This patch adds a dummy GPIO driver, which is useful for SPI devices
that do not have a physical chip select.
Signed-off-by: Steven A. Falco <sfa...@harris.com>
---
The SPI subsystem requires a chip-select for each connected slave
device. I have a custom board with an Atmel "co-processor". This part
is reprogrammed via SPI, so it needs a chip select to satisfy the SPI
subsystem, but my hardware does not have a physical CS connected.
I could waste a "no-connect" GPIO pin, but I'd rather not. So, I've
written a dummy GPIO driver, which behaves exactly like a real GPIO
device, but with no underlying hardware. This could also be useful
as a template for real GPIO drivers.
I use the following dts entry:
GPIO3: du...@ef500000 {
compatible = "linux,dummy-gpio";
reg = <ef500000 1>;
gpio-controller;
#gpio-cells = <2>;
};
Because the device is registered via of_mm_gpiochip_add, I have to
provide it a resource. The driver will ioremap this resource, but will
not touch it. So, I simply chose a reserved address in the 440EPx
address space, to satisfy that requirement. Any unused, ioremap-able
address can be used for this purpose.
I've put this into the platforms/44x/Kconfig for this example, but it
probably ought to go into sysdev/Kconfig, if it is of general interest.
Comments invited.
Steve
arch/powerpc/platforms/44x/Kconfig | 8 +++
arch/powerpc/sysdev/Makefile | 1 +
arch/powerpc/sysdev/dummy_gpio.c | 98 ++++++++++++++++++++++++++++++++++++
3 files changed, 107 insertions(+), 0 deletions(-)
create mode 100644 arch/powerpc/sysdev/dummy_gpio.c
diff --git a/arch/powerpc/platforms/44x/Kconfig
b/arch/powerpc/platforms/44x/Kconfig
index eec5cb4..5b52956 100644
--- a/arch/powerpc/platforms/44x/Kconfig
+++ b/arch/powerpc/platforms/44x/Kconfig
@@ -143,6 +143,14 @@ config XILINX_VIRTEX440_GENERIC_BOARD
Most Virtex 5 designs should use this unless it needs to do some
special configuration at board probe time.
+config DUMMY_GPIO
+ bool "Dummy GPIO support"
+ depends on 44x
+ select ARCH_REQUIRE_GPIOLIB
+ select GENERIC_GPIO
+ help
+ Enable gpiolib support for dummy devices
+
config PPC4xx_GPIO
bool "PPC4xx GPIO support"
depends on 44x
diff --git a/arch/powerpc/sysdev/Makefile b/arch/powerpc/sysdev/Makefile
index 35d5765..0f76f2a 100644
--- a/arch/powerpc/sysdev/Makefile
+++ b/arch/powerpc/sysdev/Makefile
@@ -36,6 +36,7 @@ ifeq ($(CONFIG_PCI),y)
obj-$(CONFIG_4xx) += ppc4xx_pci.o
endif
obj-$(CONFIG_PPC4xx_GPIO) += ppc4xx_gpio.o
+obj-$(CONFIG_DUMMY_GPIO) += dummy_gpio.o
# Temporary hack until we have migrated to asm-powerpc
ifeq ($(ARCH),powerpc)
diff --git a/arch/powerpc/sysdev/dummy_gpio.c b/arch/powerpc/sysdev/dummy_gpio.c
new file mode 100644
index 0000000..22f93d6
--- /dev/null
+++ b/arch/powerpc/sysdev/dummy_gpio.c
@@ -0,0 +1,98 @@
+/*
+ * Dummy gpio driver
+ *
+ * Copyright (c) 2008 Harris Corporation
+ * Copyright (c) 2008 Sascha Hauer <s.ha...@pengutronix.de>, Pengutronix
+ * Copyright (c) MontaVista Software, Inc. 2008.
+ *
+ * Author: Steve Falco <sfa...@harris.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/of_gpio.h>
+#include <linux/gpio.h>
+#include <linux/types.h>
+
+struct dummy_gpio_chip {
+ struct of_mm_gpio_chip mm_gc;
+};
+
+static int dummy_gpio_get(struct gpio_chip *gc, unsigned int gpio)
+{
+ return 0;
+}
+
+static void
+dummy_gpio_set(struct gpio_chip *gc, unsigned int gpio, int val)
+{
+}
+
+static int dummy_gpio_dir_in(struct gpio_chip *gc, unsigned int gpio)
+{
+ return 0;
+}
+
+static int
+dummy_gpio_dir_out(struct gpio_chip *gc, unsigned int gpio, int val)
+{
+ return 0;
+}
+
+static int __init dummy_add_gpiochips(void)
+{
+ struct device_node *np;
+
+ for_each_compatible_node(np, NULL, "linux,dummy-gpio") {
+ int ret;
+ struct dummy_gpio_chip *dummy_gc;
+ struct of_mm_gpio_chip *mm_gc;
+ struct of_gpio_chip *of_gc;
+ struct gpio_chip *gc;
+
+ dummy_gc = kzalloc(sizeof(*dummy_gc), GFP_KERNEL);
+ if (!dummy_gc) {
+ ret = -ENOMEM;
+ goto err;
+ }
+
+ mm_gc = &dummy_gc->mm_gc;
+ of_gc = &mm_gc->of_gc;
+ gc = &of_gc->gc;
+
+ of_gc->gpio_cells = 2;
+ gc->ngpio = 32;
+ gc->direction_input = dummy_gpio_dir_in;
+ gc->direction_output = dummy_gpio_dir_out;
+ gc->get = dummy_gpio_get;
+ gc->set = dummy_gpio_set;
+
+ ret = of_mm_gpiochip_add(np, mm_gc);
+ if (ret)
+ goto err;
+ continue;
+err:
+ pr_err("%s: registration failed with status %d\n",
+ np->full_name, ret);
+ kfree(dummy_gc);
+ /* try others anyway */
+ }
+ return 0;
+}
+arch_initcall(dummy_add_gpiochips);
--
1.6.0.2
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