From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mlbe2k2.cs.myharris.net (mlbe2k2.cs.myharris.net [137.237.90.89]) by ozlabs.org (Postfix) with ESMTP id 44F6BDE0D8 for ; Sat, 13 Dec 2008 01:22:05 +1100 (EST) Message-ID: <4942738A.80609@harris.com> Date: Fri, 12 Dec 2008 09:22:02 -0500 From: "Steven A. Falco" MIME-Version: 1.0 To: "linuxppc-dev@ozlabs.org" Subject: [RFC] Dummy GPIO driver for use with SPI Content-Type: text/plain; charset=UTF-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 --- 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: dummy@ef500000 { compatible = "linux,dummy-gpio"; reg = ; 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 , Pengutronix + * Copyright (c) MontaVista Software, Inc. 2008. + * + * Author: Steve Falco + * + * 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 +#include +#include +#include +#include +#include +#include +#include + +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