[PATCH v2] Add GPIO-based MMC/SD driver

Michael Buesch
2008-07-18T20:04:22Z

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 sysfs interface to dynamically create
and destroy GPIO-based MMC/SD card interfaces. It also provides
a platform device interface API.
See Documentation/gpiommc.txt for details.

Signed-off-by: Michael Buesch <mb@bu3sch.de>

---

This driver is used in OpenWrt since quite some time, so please
consider for inclusion in mainline.

Index: linux-next/drivers/mmc/host/gpiommc.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-next/drivers/mmc/host/gpiommc.c 2008-07-18 21:54:05.000000000 +0200
@@ -0,0 +1,328 @@
+/*
+ * 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 sysfs interface.
+ *
+ * Copyright 2008 Michael Buesch <mb@bu3sch.de>
+ *
+ * Licensed under the GNU/GPL. See COPYING for details.
+ */
+
+#include <linux/mmc/gpiommc.h>
+#include <linux/platform_device.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/spi/spi_gpio.h>
+
+
+#define PFX "gpio-mmc: "
+#define GPIOMMC_MAX_NAMELEN_STR __stringify(GPIOMMC_MAX_NAMELEN)
+
+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;
+
+ /* 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;
+}
+
+/* Wrapper for the platform data with context data for the sysfs interface. */
+struct gpiommc_sysfs_platform_data {
+ struct gpiommc_platform_data p; /* Keep as first element */
+
+ /* The platform device that we allocated. */
+ struct platform_device *pdev;
+ /* gpiommc_sysfs_list */
+ struct list_head list;
+};
+
+static LIST_HEAD(gpiommc_sysfs_list);
+static DEFINE_MUTEX(gpiommc_sysfs_mutex);
+
+static struct gpiommc_sysfs_platform_data *gpiommc_sysfs_find_dev(const char *name)
+{
+ struct gpiommc_sysfs_platform_data *pdata;
+
+ list_for_each_entry(pdata, &gpiommc_sysfs_list, list) {
+ if (strcmp(pdata->p.name, name) == 0)
+ return pdata;
+ }
+
+ return NULL;
+}
+
+static ssize_t gpiommc_add_store(struct device_driver *drv,
+ const char *buf, size_t count)
+{
+ int res, err;
+ struct gpiommc_sysfs_platform_data pdata_local, *pdata;
+ struct platform_device *pdev;
+ unsigned int no_spi_delay = 0, mode = 0, csactivelow = 0;
+
+ mutex_lock(&gpiommc_sysfs_mutex);
+
+ pdata = &pdata_local;
+ memset(pdata, 0, sizeof(*pdata));
+
+ err = -EINVAL;
+ res = sscanf(buf, "%" GPIOMMC_MAX_NAMELEN_STR "s %u %u %u %u %u %u %u %u",
+ pdata->p.name,
+ &pdata->p.pins.gpio_di,
+ &pdata->p.pins.gpio_do,
+ &pdata->p.pins.gpio_clk,
+ &pdata->p.pins.gpio_cs,
+ &mode,
+ &pdata->p.max_bus_speed,
+ &no_spi_delay,
+ &csactivelow);
+ pdata->p.mode = mode;
+ pdata->p.no_spi_delay = !!no_spi_delay;
+ pdata->p.pins.cs_activelow = !!csactivelow;
+ if (res < 9)
+ pdata->p.pins.cs_activelow = 1; /* Default: CS = activelow */
+ if (res < 8)
+ pdata->p.no_spi_delay = 0; /* Default: Delay turned on */
+ if (res < 7)
+ pdata->p.max_bus_speed = 5000000; /* Default: 5Mhz */
+ if (res < 6)
+ pdata->p.mode = 0; /* Default: SPI mode 0 */
+ if (res < 5 || res > 9)
+ goto out; /* First 5 args are mandatory. */
+
+ /* Convert mode so that the SPI subsystem does understand it. */
+ switch (pdata->p.mode) {
+ case 0:
+ pdata->p.mode = SPI_MODE_0;
+ break;
+ case 1:
+ pdata->p.mode = SPI_MODE_1;
+ break;
+ case 2:
+ pdata->p.mode = SPI_MODE_2;
+ break;
+ case 3:
+ pdata->p.mode = SPI_MODE_3;
+ break;
+ default:
+ goto out; /* Invalid mode */
+ }
+
+ err = -EEXIST;
+ if (gpiommc_sysfs_find_dev(pdata->p.name))
+ goto out;
+
+ err = -ENOMEM;
+ pdev = platform_device_alloc(GPIOMMC_PLATDEV_NAME, gpiommc_next_id());
+ if (!pdev)
+ goto out;
+
+ err = platform_device_add_data(pdev, pdata, sizeof(*pdata));
+ if (err)
+ goto err_free_pdev;
+ pdata = pdev->dev.platform_data;
+
+ err = platform_device_add(pdev);
+ if (err)
+ goto err_free_pdev;
+
+ pdata->pdev = pdev;
+ INIT_LIST_HEAD(&pdata->list);
+ list_add(&pdata->list, &gpiommc_sysfs_list);
+
+ err = 0;
+out:
+ mutex_unlock(&gpiommc_sysfs_mutex);
+
+ return err ? err : count;
+
+err_free_pdev:
+ platform_device_put(pdev);
+ goto out;
+}
+
+static ssize_t gpiommc_remove_store(struct device_driver *drv,
+ const char *buf, size_t count)
+{
+ struct gpiommc_sysfs_platform_data *pdata;
+ int err;
+
+ mutex_lock(&gpiommc_sysfs_mutex);
+
+ err = -ENODEV;
+ pdata = gpiommc_sysfs_find_dev(buf);
+ if (!pdata)
+ goto out;
+
+ list_del(&pdata->list);
+ platform_device_unregister(pdata->pdev);
+
+out:
+ mutex_unlock(&gpiommc_sysfs_mutex);
+
+ return err ? err : count;
+}
+
+static DRIVER_ATTR(add, 0200,
+ NULL, gpiommc_add_store);
+static DRIVER_ATTR(remove, 0200,
+ NULL, gpiommc_remove_store);
+
+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;
+ err = driver_create_file(&gpiommc_plat_driver.driver,
+ &driver_attr_add);
+ if (err)
+ goto err_drv_unreg;
+ err = driver_create_file(&gpiommc_plat_driver.driver,
+ &driver_attr_remove);
+ if (err)
+ goto err_remove_add;
+
+ return 0;
+
+err_remove_add:
+ driver_remove_file(&gpiommc_plat_driver.driver,
+ &driver_attr_add);
+err_drv_unreg:
+ platform_driver_unregister(&gpiommc_plat_driver);
+ return err;
+}
+module_init(gpiommc_modinit);
+
+static void __exit gpiommc_modexit(void)
+{
+ struct gpiommc_sysfs_platform_data *pdata, *pdata_tmp;
+
+ driver_remove_file(&gpiommc_plat_driver.driver,
+ &driver_attr_remove);
+ driver_remove_file(&gpiommc_plat_driver.driver,
+ &driver_attr_add);
+
+ mutex_lock(&gpiommc_sysfs_mutex);
+ list_for_each_entry_safe(pdata, pdata_tmp, &gpiommc_sysfs_list, list) {
+ list_del(&pdata->list);
+ platform_device_unregister(pdata->pdev);
+ }
+ mutex_unlock(&gpiommc_sysfs_mutex);
+
+ platform_driver_unregister(&gpiommc_plat_driver);
+}
+module_exit(gpiommc_modexit);
Index: linux-next/drivers/mmc/host/Kconfig
===================================================================
--- linux-next.orig/drivers/mmc/host/Kconfig 2008-07-18 21:52:46.000000000 +0200
+++ linux-next/drivers/mmc/host/Kconfig 2008-07-18 21:57:08.000000000 +0200
@@ -164,3 +164,23 @@ config MMC_S3C

If unsure, say N.

+config GPIOMMC
+ tristate "MMC/SD over GPIO-based SPI"
+ depends on MMC && MMC_SPI && SPI_GPIO
+ 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 sysfs interface to dynamically create
+ and destroy GPIO-based MMC/SD card interfaces. 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 MMC_S3C
+ tristate "Samsung S3C SD/MMC Card Interface support"
+ depends on ARCH_S3C2410 && MMC
Index: linux-next/drivers/mmc/host/Makefile
===================================================================
--- linux-next.orig/drivers/mmc/host/Makefile 2008-07-18 21:52:46.000000000 +0200
+++ linux-next/drivers/mmc/host/Makefile 2008-07-18 21:54:19.000000000 +0200
@@ -20,3 +20,4 @@ obj-$(CONFIG_MMC_ATMELMCI) += atmel-mci.
obj-$(CONFIG_MMC_TIFM_SD) += tifm_sd.o
obj-$(CONFIG_MMC_SPI) += mmc_spi.o
obj-$(CONFIG_MMC_S3C) += s3cmci.o
+obj-$(CONFIG_GPIOMMC) += gpiommc.o
Index: linux-next/include/linux/mmc/gpiommc.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-next/include/linux/mmc/gpiommc.h 2008-07-18 21:54:05.000000000 +0200
@@ -0,0 +1,62 @@
+/*
+ * 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
+
+/** 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_ */
Index: linux-next/Documentation/gpiommc.txt
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-next/Documentation/gpiommc.txt 2008-07-18 21:54:05.000000000 +0200
@@ -0,0 +1,96 @@
+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 sysfs 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.
+Now simply register the platform device.
+
+ err = platform_device_add(pdev);
+
+Done. The gpiommc probe routine should be called and you should see a dmesg
+message for the added device.
+
+
+Registering devices via sysfs
+=============================
+
+MMC/SD cards connected via GPIO often are a pretty dynamic thing. 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.
+
+There are two sysfs files responsible for that:
+export ADD=/sys/bus/platform/drivers/gpiommc/add
+export REMOVE=/sys/bus/platform/drivers/gpiommc/remove
+
+To add a new device, simply echo the configuration string to the "add" file.
+The config string is composed out of the following elements:
+
+DEVNAME DIpin DOpin CLKpin CSpin SPIMODE MAXBUSSPEED NO_SPI_DELAY CSACTIVELOW
+
+DEVNAME is a unique name string for the device.
+DIpin is the SPI DI GPIO pin.
+DOpin is the SPI DO GPIO pin.
+CLKpin is the SPI CLOCK GPIO pin.
+CSpin is the SPI CHIPSELECT GPIO pin.
+SPIMODE is the hardware mode the device will run at. Can be 0-3.
+MAXBUSSPEED is the maximum bus speed in Hertz.
+NO_SPI_DELAY can be 1 or 0. If it is 1, then the lowlevel SPI delay
+will not be performed. This is not standards compliant, but may be required
+to gain reasonable speeds on embedded hardware.
+CSACTIVELOW can be 1 or 0. If it is 1, the chip is considered to be selected, if CS
+is at a logical 0.
+
+Note that the elements SPIMODE, MAXBUSSPEED and NO_SPI_DELAY are optional
+and can be omitted.
+SPIMODE will default to 0.
+MAXBUSSSPEED will default to 5Mhz.
+NO_SPI_DELAY will default to 0.
+CSACTIVELOW will default to 1.
+
+Example:
+
+ echo -n "my_device 5 4 3 7 0 1000000 1" > $ADD
+
+This will add a new device called "my_device" with the GPIO pins assigned as
+DI=5, DO=4, CLK=3, CS=7
+The hardware mode will be SPI_MODE_0.
+The maximum bus speed will be 1000000 Hz (1Mhz)
+And the explicit SPI delay at the lowlevel bitbang loop will be switched off.
+
+To remove a device, simply echo the device name string to the "remove" file.
+
+Example:
+
+ echo -n "my_device" > $REMOVE
Index: linux-next/MAINTAINERS
===================================================================
--- linux-next.orig/MAINTAINERS 2008-07-18 21:54:00.000000000 +0200
+++ linux-next/MAINTAINERS 2008-07-18 21:54:05.000000000 +0200
@@ -1875,6 +1875,11 @@ L: gigaset307x-common@lists.sourceforge.
W: http://gigaset307x.sourceforge.net/
S: Maintained

+GPIOMMC DRIVER
+P: Michael Buesch
+M: mb@bu3sch.de
+S: Maintained
+
HARDWARE MONITORING
P: Mark M. Hoffman
M: mhoffman@lightlink.com

--
Greetings Michael.