path: root/target/linux/generic/patches-4.1/863-gpiommc.patch

--- /dev/null
+++ b/drivers/mmc/host/gpiommc.c
@@ -0,0 +1,609 @@
+/*
+ * Driver an MMC/SD card on a bitbanging GPIO SPI bus.
+ * This module hooks up the mmc_spi and spi_gpio modules and also
+ * provides a configfs interface.
+ *
+ * Copyright 2008 Michael Buesch <mb@bu3sch.de>
+ *
+ * Licensed under the GNU/GPL. See COPYING for details.
+ */
+
+#include <linux/module.h>
+#include <linux/mmc/gpiommc.h>
+#include <linux/platform_device.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/spi/spi_gpio_old.h>
+#include <linux/configfs.h>
+#include <linux/gpio.h>
+#include <asm/atomic.h>
+
+
+#define PFX				"gpio-mmc: "
+
+
+struct gpiommc_device {
+	struct platform_device *pdev;
+	struct platform_device *spi_pdev;
+	struct spi_board_info boardinfo;
+};
+
+
+MODULE_DESCRIPTION("GPIO based MMC driver");
+MODULE_AUTHOR("Michael Buesch");
+MODULE_LICENSE("GPL");
+
+
+static int gpiommc_boardinfo_setup(struct spi_board_info *bi,
+				   struct spi_master *master,
+				   void *data)
+{
+	struct gpiommc_device *d = data;
+	struct gpiommc_platform_data *pdata = d->pdev->dev.platform_data;
+
+	/* Bind the SPI master to the MMC-SPI host driver. */
+	strlcpy(bi->modalias, "mmc_spi", sizeof(bi->modalias));
+
+	bi->max_speed_hz = pdata->max_bus_speed;
+	bi->bus_num = master->bus_num;
+	bi->mode = pdata->mode;
+
+	return 0;
+}
+
+static int gpiommc_probe(struct platform_device *pdev)
+{
+	struct gpiommc_platform_data *mmc_pdata = pdev->dev.platform_data;
+	struct spi_gpio_platform_data spi_pdata;
+	struct gpiommc_device *d;
+	int err;
+
+	err = -ENXIO;
+	if (!mmc_pdata)
+		goto error;
+
+#ifdef CONFIG_MMC_SPI_MODULE
+	err = request_module("mmc_spi");
+	if (err) {
+		printk(KERN_WARNING PFX
+		       "Failed to request mmc_spi module.\n");
+	}
+#endif /* CONFIG_MMC_SPI_MODULE */
+
+	/* Allocate the GPIO-MMC device */
+	err = -ENOMEM;
+	d = kzalloc(sizeof(*d), GFP_KERNEL);
+	if (!d)
+		goto error;
+	d->pdev = pdev;
+
+	/* Create the SPI-GPIO device */
+	d->spi_pdev = platform_device_alloc(SPI_GPIO_PLATDEV_NAME,
+					    spi_gpio_next_id());
+	if (!d->spi_pdev)
+		goto err_free_d;
+
+	memset(&spi_pdata, 0, sizeof(spi_pdata));
+	spi_pdata.pin_clk = mmc_pdata->pins.gpio_clk;
+	spi_pdata.pin_miso = mmc_pdata->pins.gpio_do;
+	spi_pdata.pin_mosi = mmc_pdata->pins.gpio_di;
+	spi_pdata.pin_cs = mmc_pdata->pins.gpio_cs;
+	spi_pdata.cs_activelow = mmc_pdata->pins.cs_activelow;
+	spi_pdata.no_spi_delay = mmc_pdata->no_spi_delay;
+	spi_pdata.boardinfo_setup = gpiommc_boardinfo_setup;
+	spi_pdata.boardinfo_setup_data = d;
+
+	err = platform_device_add_data(d->spi_pdev, &spi_pdata,
+				       sizeof(spi_pdata));
+	if (err)
+		goto err_free_pdev;
+	err = platform_device_add(d->spi_pdev);
+	if (err)
+		goto err_free_pdata;
+	platform_set_drvdata(pdev, d);
+
+	printk(KERN_INFO PFX "MMC-Card \"%s\" "
+	       "attached to GPIO pins di=%u, do=%u, clk=%u, cs=%u\n",
+	       mmc_pdata->name, mmc_pdata->pins.gpio_di,
+	       mmc_pdata->pins.gpio_do,
+	       mmc_pdata->pins.gpio_clk,
+	       mmc_pdata->pins.gpio_cs);
+
+	return 0;
+
+err_free_pdata:
+	kfree(d->spi_pdev->dev.platform_data);
+	d->spi_pdev->dev.platform_data = NULL;
+err_free_pdev:
+	platform_device_put(d->spi_pdev);
+err_free_d:
+	kfree(d);
+error:
+	return err;
+}
+
+static int gpiommc_remove(struct platform_device *pdev)
+{
+	struct gpiommc_device *d = platform_get_drvdata(pdev);
+	struct gpiommc_platform_data *pdata = d->pdev->dev.platform_data;
+
+	platform_device_unregister(d->spi_pdev);
+	printk(KERN_INFO PFX "GPIO based MMC-Card \"%s\" removed\n",
+	       pdata->name);
+	platform_device_put(d->spi_pdev);
+
+	return 0;
+}
+
+#ifdef CONFIG_GPIOMMC_CONFIGFS
+
+/* A device that was created through configfs */
+struct gpiommc_configfs_device {
+	struct config_item item;
+	/* The platform device, after registration. */
+	struct platform_device *pdev;
+	/* The configuration */
+	struct gpiommc_platform_data pdata;
+};
+
+#define GPIO_INVALID	-1
+
+static inline bool gpiommc_is_registered(struct gpiommc_configfs_device *dev)
+{
+	return (dev->pdev != NULL);
+}
+
+static inline struct gpiommc_configfs_device *ci_to_gpiommc(struct config_item *item)
+{
+	return item ? container_of(item, struct gpiommc_configfs_device, item) : NULL;
+}
+
+static struct configfs_attribute gpiommc_attr_DI = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "gpio_data_in",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute gpiommc_attr_DO = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "gpio_data_out",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute gpiommc_attr_CLK = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "gpio_clock",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute gpiommc_attr_CS = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "gpio_chipselect",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute gpiommc_attr_CS_activelow = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "gpio_chipselect_activelow",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute gpiommc_attr_spimode = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "spi_mode",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute gpiommc_attr_spidelay = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "spi_delay",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute gpiommc_attr_max_bus_speed = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "max_bus_speed",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute gpiommc_attr_register = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "register",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute *gpiommc_config_attrs[] = {
+	&gpiommc_attr_DI,
+	&gpiommc_attr_DO,
+	&gpiommc_attr_CLK,
+	&gpiommc_attr_CS,
+	&gpiommc_attr_CS_activelow,
+	&gpiommc_attr_spimode,
+	&gpiommc_attr_spidelay,
+	&gpiommc_attr_max_bus_speed,
+	&gpiommc_attr_register,
+	NULL,
+};
+
+static ssize_t gpiommc_config_attr_show(struct config_item *item,
+					struct configfs_attribute *attr,
+					char *page)
+{
+	struct gpiommc_configfs_device *dev = ci_to_gpiommc(item);
+	ssize_t count = 0;
+	unsigned int gpio;
+	int err = 0;
+
+	if (attr == &gpiommc_attr_DI) {
+		gpio = dev->pdata.pins.gpio_di;
+		if (gpio == GPIO_INVALID)
+			count = snprintf(page, PAGE_SIZE, "not configured\n");
+		else
+			count = snprintf(page, PAGE_SIZE, "%u\n", gpio);
+		goto out;
+	}
+	if (attr == &gpiommc_attr_DO) {
+		gpio = dev->pdata.pins.gpio_do;
+		if (gpio == GPIO_INVALID)
+			count = snprintf(page, PAGE_SIZE, "not configured\n");
+		else
+			count = snprintf(page, PAGE_SIZE, "%u\n", gpio);
+		goto out;
+	}
+	if (attr == &gpiommc_attr_CLK) {
+		gpio = dev->pdata.pins.gpio_clk;
+		if (gpio == GPIO_INVALID)
+			count = snprintf(page, PAGE_SIZE, "not configured\n");
+		else
+			count = snprintf(page, PAGE_SIZE, "%u\n", gpio);
+		goto out;
+	}
+	if (attr == &gpiommc_attr_CS) {
+		gpio = dev->pdata.pins.gpio_cs;
+		if (gpio == GPIO_INVALID)
+			count = snprintf(page, PAGE_SIZE, "not configured\n");
+		else
+			count = snprintf(page, PAGE_SIZE, "%u\n", gpio);
+		goto out;
+	}
+	if (attr == &gpiommc_attr_CS_activelow) {
+		count = snprintf(page, PAGE_SIZE, "%u\n",
+				 dev->pdata.pins.cs_activelow);
+		goto out;
+	}
+	if (attr == &gpiommc_attr_spimode) {
+		count = snprintf(page, PAGE_SIZE, "%u\n",
+				 dev->pdata.mode);
+		goto out;
+	}
+	if (attr == &gpiommc_attr_spidelay) {
+		count = snprintf(page, PAGE_SIZE, "%u\n",
+				 !dev->pdata.no_spi_delay);
+		goto out;
+	}
+	if (attr == &gpiommc_attr_max_bus_speed) {
+		count = snprintf(page, PAGE_SIZE, "%u\n",
+				 dev->pdata.max_bus_speed);
+		goto out;
+	}
+	if (attr == &gpiommc_attr_register) {
+		count = snprintf(page, PAGE_SIZE, "%u\n",
+				 gpiommc_is_registered(dev));
+		goto out;
+	}
+	WARN_ON(1);
+	err = -ENOSYS;
+out:
+	return err ? err : count;
+}
+
+static int gpiommc_do_register(struct gpiommc_configfs_device *dev,
+			       const char *name)
+{
+	int err;
+
+	if (gpiommc_is_registered(dev))
+		return 0;
+
+	if (!gpio_is_valid(dev->pdata.pins.gpio_di) ||
+	    !gpio_is_valid(dev->pdata.pins.gpio_do) ||
+	    !gpio_is_valid(dev->pdata.pins.gpio_clk) ||
+	    !gpio_is_valid(dev->pdata.pins.gpio_cs)) {
+		printk(KERN_ERR PFX
+		       "configfs: Invalid GPIO pin number(s)\n");
+		return -EINVAL;
+	}
+
+	strlcpy(dev->pdata.name, name,
+		sizeof(dev->pdata.name));
+
+	dev->pdev = platform_device_alloc(GPIOMMC_PLATDEV_NAME,
+					  gpiommc_next_id());
+	if (!dev->pdev)
+		return -ENOMEM;
+	err = platform_device_add_data(dev->pdev, &dev->pdata,
+				       sizeof(dev->pdata));
+	if (err) {
+		platform_device_put(dev->pdev);
+		return err;
+	}
+	err = platform_device_add(dev->pdev);
+	if (err) {
+		platform_device_put(dev->pdev);
+		return err;
+	}
+
+	return 0;
+}
+
+static void gpiommc_do_unregister(struct gpiommc_configfs_device *dev)
+{
+	if (!gpiommc_is_registered(dev))
+		return;
+
+	platform_device_unregister(dev->pdev);
+	dev->pdev = NULL;
+}
+
+static ssize_t gpiommc_config_attr_store(struct config_item *item,
+					 struct configfs_attribute *attr,
+					 const char *page, size_t count)
+{
+	struct gpiommc_configfs_device *dev = ci_to_gpiommc(item);
+	int err = -EINVAL;
+	unsigned long data;
+
+	if (attr == &gpiommc_attr_register) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		if (data == 1)
+			err = gpiommc_do_register(dev, item->ci_name);
+		if (data == 0) {
+			gpiommc_do_unregister(dev);
+			err = 0;
+		}
+		goto out;
+	}
+
+	if (gpiommc_is_registered(dev)) {
+		/* The rest of the config parameters can only be set
+		 * as long as the device is not registered, yet. */
+		err = -EBUSY;
+		goto out;
+	}
+
+	if (attr == &gpiommc_attr_DI) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		if (!gpio_is_valid(data))
+			goto out;
+		dev->pdata.pins.gpio_di = data;
+		err = 0;
+		goto out;
+	}
+	if (attr == &gpiommc_attr_DO) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		if (!gpio_is_valid(data))
+			goto out;
+		dev->pdata.pins.gpio_do = data;
+		err = 0;
+		goto out;
+	}
+	if (attr == &gpiommc_attr_CLK) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		if (!gpio_is_valid(data))
+			goto out;
+		dev->pdata.pins.gpio_clk = data;
+		err = 0;
+		goto out;
+	}
+	if (attr == &gpiommc_attr_CS) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		if (!gpio_is_valid(data))
+			goto out;
+		dev->pdata.pins.gpio_cs = data;
+		err = 0;
+		goto out;
+	}
+	if (attr == &gpiommc_attr_CS_activelow) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		if (data != 0 && data != 1)
+			goto out;
+		dev->pdata.pins.cs_activelow = data;
+		err = 0;
+		goto out;
+	}
+	if (attr == &gpiommc_attr_spimode) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		switch (data) {
+		case 0:
+			dev->pdata.mode = SPI_MODE_0;
+			break;
+		case 1:
+			dev->pdata.mode = SPI_MODE_1;
+			break;
+		case 2:
+			dev->pdata.mode = SPI_MODE_2;
+			break;
+		case 3:
+			dev->pdata.mode = SPI_MODE_3;
+			break;
+		default:
+			goto out;
+		}
+		err = 0;
+		goto out;
+	}
+	if (attr == &gpiommc_attr_spidelay) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		if (data != 0 && data != 1)
+			goto out;
+		dev->pdata.no_spi_delay = !data;
+		err = 0;
+		goto out;
+	}
+	if (attr == &gpiommc_attr_max_bus_speed) {
+		err = kstrtoul(page, 10, &data);
+		if (err)
+			goto out;
+		err = -EINVAL;
+		if (data > UINT_MAX)
+			goto out;
+		dev->pdata.max_bus_speed = data;
+		err = 0;
+		goto out;
+	}
+	WARN_ON(1);
+	err = -ENOSYS;
+out:
+	return err ? err : count;
+}
+
+static void gpiommc_config_item_release(struct config_item *item)
+{
+	struct gpiommc_configfs_device *dev = ci_to_gpiommc(item);
+
+	kfree(dev);
+}
+
+static struct configfs_item_operations gpiommc_config_item_ops = {
+	.release		= gpiommc_config_item_release,
+	.show_attribute		= gpiommc_config_attr_show,
+	.store_attribute	= gpiommc_config_attr_store,
+};
+
+static struct config_item_type gpiommc_dev_ci_type = {
+	.ct_item_ops	= &gpiommc_config_item_ops,
+	.ct_attrs	= gpiommc_config_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct config_item *gpiommc_make_item(struct config_group *group,
+					     const char *name)
+{
+	struct gpiommc_configfs_device *dev;
+
+	if (strlen(name) > GPIOMMC_MAX_NAMELEN) {
+		printk(KERN_ERR PFX "configfs: device name too long\n");
+		return NULL;
+	}
+
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev)
+		return NULL;
+
+	config_item_init_type_name(&dev->item, name,
+				   &gpiommc_dev_ci_type);
+
+	/* Assign default configuration */
+	dev->pdata.pins.gpio_di = GPIO_INVALID;
+	dev->pdata.pins.gpio_do = GPIO_INVALID;
+	dev->pdata.pins.gpio_clk = GPIO_INVALID;
+	dev->pdata.pins.gpio_cs = GPIO_INVALID;
+	dev->pdata.pins.cs_activelow = 1;
+	dev->pdata.mode = SPI_MODE_0;
+	dev->pdata.no_spi_delay = 0;
+	dev->pdata.max_bus_speed = 5000000; /* 5 MHz */
+
+	return &(dev->item);
+}
+
+static void gpiommc_drop_item(struct config_group *group,
+			      struct config_item *item)
+{
+	struct gpiommc_configfs_device *dev = ci_to_gpiommc(item);
+
+	gpiommc_do_unregister(dev);
+	kfree(dev);
+}
+
+static struct configfs_group_operations gpiommc_ct_group_ops = {
+	.make_item	= gpiommc_make_item,
+	.drop_item	= gpiommc_drop_item,
+};
+
+static struct config_item_type gpiommc_ci_type = {
+	.ct_group_ops	= &gpiommc_ct_group_ops,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct configfs_subsystem gpiommc_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf = GPIOMMC_PLATDEV_NAME,
+			.ci_type = &gpiommc_ci_type,
+		},
+	},
+	.su_mutex = __MUTEX_INITIALIZER(gpiommc_subsys.su_mutex),
+};
+
+#endif /* CONFIG_GPIOMMC_CONFIGFS */
+
+static struct platform_driver gpiommc_plat_driver = {
+	.probe	= gpiommc_probe,
+	.remove	= gpiommc_remove,
+	.driver	= {
+		.name	= GPIOMMC_PLATDEV_NAME,
+		.owner	= THIS_MODULE,
+	},
+};
+
+int gpiommc_next_id(void)
+{
+	static atomic_t counter = ATOMIC_INIT(-1);
+
+	return atomic_inc_return(&counter);
+}
+EXPORT_SYMBOL(gpiommc_next_id);
+
+static int __init gpiommc_modinit(void)
+{
+	int err;
+
+	err = platform_driver_register(&gpiommc_plat_driver);
+	if (err)
+		return err;
+
+#ifdef CONFIG_GPIOMMC_CONFIGFS
+	config_group_init(&gpiommc_subsys.su_group);
+	err = configfs_register_subsystem(&gpiommc_subsys);
+	if (err) {
+		platform_driver_unregister(&gpiommc_plat_driver);
+		return err;
+	}
+#endif /* CONFIG_GPIOMMC_CONFIGFS */
+
+	return 0;
+}
+module_init(gpiommc_modinit);
+
+static void __exit gpiommc_modexit(void)
+{
+#ifdef CONFIG_GPIOMMC_CONFIGFS
+	configfs_unregister_subsystem(&gpiommc_subsys);
+#endif
+	platform_driver_unregister(&gpiommc_plat_driver);
+}
+module_exit(gpiommc_modexit);
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -556,6 +556,31 @@ config MMC_SDHI
 	  This provides support for the SDHI SD/SDIO controller found in
 	  SuperH and ARM SH-Mobile SoCs
 
+config GPIOMMC
+	tristate "MMC/SD over GPIO-based SPI"
+	depends on MMC && MMC_SPI && SPI_GPIO_OLD
+	help
+	  This driver hooks up the mmc_spi and spi_gpio modules so that
+	  MMC/SD cards can be used on a GPIO based bus by bitbanging
+	  the SPI protocol in software.
+
+	  This driver provides a configfs interface to dynamically create
+	  and destroy GPIO-based MMC/SD card devices. It also provides
+	  a platform device interface API.
+	  See Documentation/gpiommc.txt for details.
+
+	  The module will be called gpiommc.
+
+	  If unsure, say N.
+
+config GPIOMMC_CONFIGFS
+	bool
+	depends on GPIOMMC && CONFIGFS_FS
+	default y
+	help
+	  This option automatically enables configfs support for gpiommc
+	  if configfs is available.
+
 config MMC_CB710
 	tristate "ENE CB710 MMC/SD Interface support"
 	depends on PCI
--- a/drivers/mmc/host/Makefile
+++ b/drivers/mmc/host/Makefile
@@ -40,6 +40,7 @@ tmio_mmc_core-$(subst m,y,$(CONFIG_MMC_S
 obj-$(CONFIG_MMC_SDHI)		+= sh_mobile_sdhi.o
 obj-$(CONFIG_MMC_CB710)		+= cb710-mmc.o
 obj-$(CONFIG_MMC_VIA_SDMMC)	+= via-sdmmc.o
+obj-$(CONFIG_GPIOMMC)		+= gpiommc.o
 obj-$(CONFIG_SDH_BFIN)		+= bfin_sdh.o
 obj-$(CONFIG_MMC_DW)		+= dw_mmc.o
 obj-$(CONFIG_MMC_DW_PLTFM)	+= dw_mmc-pltfm.o
--- /dev/null
+++ b/include/linux/mmc/gpiommc.h
@@ -0,0 +1,71 @@
+/*
+ * Device driver for MMC/SD cards driven over a GPIO bus.
+ *
+ * Copyright (c) 2008 Michael Buesch
+ *
+ * Licensed under the GNU/GPL version 2.
+ */
+#ifndef LINUX_GPIOMMC_H_
+#define LINUX_GPIOMMC_H_
+
+#include <linux/types.h>
+
+
+#define GPIOMMC_MAX_NAMELEN		15
+#define GPIOMMC_MAX_NAMELEN_STR		__stringify(GPIOMMC_MAX_NAMELEN)
+
+/**
+ * struct gpiommc_pins - Hardware pin assignments
+ *
+ * @gpio_di: The GPIO number of the DATA IN pin
+ * @gpio_do: The GPIO number of the DATA OUT pin
+ * @gpio_clk: The GPIO number of the CLOCK pin
+ * @gpio_cs: The GPIO number of the CHIPSELECT pin
+ * @cs_activelow: If true, the chip is considered selected if @gpio_cs is low.
+ */
+struct gpiommc_pins {
+	unsigned int gpio_di;
+	unsigned int gpio_do;
+	unsigned int gpio_clk;
+	unsigned int gpio_cs;
+	bool cs_activelow;
+};
+
+/**
+ * struct gpiommc_platform_data - Platform data for a MMC-over-SPI-GPIO device.
+ *
+ * @name: The unique name string of the device.
+ * @pins: The hardware pin assignments.
+ * @mode: The hardware mode. This is either SPI_MODE_0,
+ *        SPI_MODE_1, SPI_MODE_2 or SPI_MODE_3. See the SPI documentation.
+ * @no_spi_delay: Do not use delays in the lowlevel SPI bitbanging code.
+ *                This is not standards compliant, but may be required for some
+ *                embedded machines to gain reasonable speed.
+ * @max_bus_speed: The maximum speed of the SPI bus, in Hertz.
+ */
+struct gpiommc_platform_data {
+	char name[GPIOMMC_MAX_NAMELEN + 1];
+	struct gpiommc_pins pins;
+	u8 mode;
+	bool no_spi_delay;
+	unsigned int max_bus_speed;
+};
+
+/**
+ * GPIOMMC_PLATDEV_NAME - The platform device name string.
+ *
+ * The name string that has to be used for platform_device_alloc
+ * when allocating a gpiommc device.
+ */
+#define GPIOMMC_PLATDEV_NAME	"gpiommc"
+
+/**
+ * gpiommc_next_id - Get another platform device ID number.
+ *
+ * This returns the next platform device ID number that has to be used
+ * for platform_device_alloc. The ID is opaque and should not be used for
+ * anything else.
+ */
+int gpiommc_next_id(void);
+
+#endif /* LINUX_GPIOMMC_H_ */
--- /dev/null
+++ b/Documentation/gpiommc.txt
@@ -0,0 +1,97 @@
+GPIOMMC - Driver for an MMC/SD card on a bitbanging GPIO SPI bus
+================================================================
+
+The gpiommc module hooks up the mmc_spi and spi_gpio modules for running an
+MMC or SD card on GPIO pins.
+
+Two interfaces for registering a new MMC/SD card device are provided:
+A static platform-device based mechanism and a dynamic configfs based interface.
+
+
+Registering devices via platform-device
+=======================================
+
+The platform-device interface is used for registering MMC/SD devices that are
+part of the hardware platform. This is most useful only for embedded machines
+with MMC/SD devices statically connected to the platform GPIO bus.
+
+The data structures are declared in <linux/mmc/gpiommc.h>.
+
+To register a new device, define an instance of struct gpiommc_platform_data.
+This structure holds any information about how the device is hooked up to the
+GPIO pins and what hardware modes the device supports. See the docbook-style
+documentation in the header file for more information on the struct fields.
+
+Then allocate a new instance of a platform device by doing:
+
+	pdev = platform_device_alloc(GPIOMMC_PLATDEV_NAME, gpiommc_next_id());
+
+This will allocate the platform device data structures and hook it up to the
+gpiommc driver.
+Then add the gpiommc_platform_data to the platform device.
+
+	err = platform_device_add_data(pdev, pdata, sizeof(struct gpiommc_platform_data));
+
+You may free the local instance of struct gpiommc_platform_data now. (So the
+struct may be allocated on the stack, too).
+Now simply register the platform device.
+
+	err = platform_device_add(pdev);
+
+Done. The gpiommc probe routine will be invoked now and you should see a kernel
+log message for the added device.
+
+
+Registering devices via configfs
+================================
+
+MMC/SD cards connected via GPIO often are a pretty dynamic thing, as for example
+selfmade hacks for soldering an MMC/SD card to standard GPIO pins on embedded
+hardware are a common situation.
+So we provide a dynamic interface to conveniently handle adding and removing
+devices from userspace, without the need to recompile the kernel.
+
+The "gpiommc" subdirectory at the configfs mountpoint is used for handling
+the dynamic configuration.
+
+To create a new device, it must first be allocated with mkdir.
+The following command will allocate a device named "my_mmc":
+	mkdir /config/gpiommc/my_mmc
+
+There are several configuration files available in the new
+/config/gpiommc/my_mmc/ directory:
+
+gpio_data_in			= The SPI data-IN GPIO pin number.
+gpio_data_out			= The SPI data-OUT GPIO pin number.
+gpio_clock			= The SPI Clock GPIO pin number.
+gpio_chipselect			= The SPI Chipselect GPIO pin number.
+gpio_chipselect_activelow	= Boolean. If 0, Chipselect is active-HIGH.
+				  If 1, Chipselect is active-LOW.
+spi_mode			= The SPI data mode. Can be 0-3.
+spi_delay			= Enable all delays in the lowlevel bitbanging.
+max_bus_speed			= The maximum SPI bus speed. In Hertz.
+
+register			= Not a configuration parameter.
+				  Used to register the configured card
+				  with the kernel.
+
+The device must first get configured and then registered by writing "1" to
+the "register" file.
+The configuration parameters "gpio_data_in", "gpio_data_out", "gpio_clock"
+and "gpio_chipselect" are essential and _must_ be configured before writing
+"1" to the "register" file. The registration will fail, otherwise.
+
+The default values for the other parameters are:
+gpio_chipselect_activelow	= 1		(CS active-LOW)
+spi_mode			= 0		(SPI_MODE_0)
+spi_delay			= 1		(enabled)
+max_bus_speed			= 5000000	(5 Mhz)
+
+Configuration values can not be changed after registration. To unregister
+the device, write a "0" to the "register" file. The configuration can be
+changed again after unregistering.
+
+To completely remove the device, simply rmdir the directory
+(/config/gpiommc/my_mmc in this example).
+There's no need to first unregister the device before removing it. That will
+be done automatically.
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4541,6 +4541,11 @@ T:	git git://linuxtv.org/anttip/media_tr
 S:	Maintained
 F:	drivers/media/usb/hackrf/
 
+GPIOMMC DRIVER
+P:	Michael Buesch
+M:	mb@bu3sch.de
+S:	Maintained
+
 HARDWARE MONITORING
 M:	Jean Delvare <jdelvare@suse.de>
 M:	Guenter Roeck <linux@roeck-us.net>