firmware: introduce sysfs driver for QEMU's fw_cfg device
authorGabriel Somlo <somlo@cmu.edu>
Thu, 28 Jan 2016 14:23:11 +0000 (09:23 -0500)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 10 Feb 2016 01:37:39 +0000 (17:37 -0800)
Make fw_cfg entries of type "file" available via sysfs. Entries
are listed under /sys/firmware/qemu_fw_cfg/by_key, in folders
named after each entry's selector key. Filename, selector value,
and size read-only attributes are included for each entry. Also,
a "raw" attribute allows retrieval of the full binary content of
each entry.

The fw_cfg device can be instantiated automatically from ACPI or
the Device Tree, or manually by using a kernel module (or command
line) parameter, with a syntax outlined in the documentation file.

Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg [new file with mode: 0644]
drivers/firmware/Kconfig
drivers/firmware/Makefile
drivers/firmware/qemu_fw_cfg.c [new file with mode: 0644]

diff --git a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
new file mode 100644 (file)
index 0000000..e9e58d4
--- /dev/null
@@ -0,0 +1,58 @@
+What:          /sys/firmware/qemu_fw_cfg/
+Date:          August 2015
+Contact:       Gabriel Somlo <somlo@cmu.edu>
+Description:
+               Several different architectures supported by QEMU (x86, arm,
+               sun4*, ppc/mac) are provisioned with a firmware configuration
+               (fw_cfg) device, originally intended as a way for the host to
+               provide configuration data to the guest firmware. Starting
+               with QEMU v2.4, arbitrary fw_cfg file entries may be specified
+               by the user on the command line, which makes fw_cfg additionally
+               useful as an out-of-band, asynchronous mechanism for providing
+               configuration data to the guest userspace.
+
+               The authoritative guest-side hardware interface documentation
+               to the fw_cfg device can be found in "docs/specs/fw_cfg.txt"
+               in the QEMU source tree.
+
+               === SysFS fw_cfg Interface ===
+
+               The fw_cfg sysfs interface described in this document is only
+               intended to display discoverable blobs (i.e., those registered
+               with the file directory), as there is no way to determine the
+               presence or size of "legacy" blobs (with selector keys between
+               0x0002 and 0x0018) programmatically.
+
+               All fw_cfg information is shown under:
+
+                       /sys/firmware/qemu_fw_cfg/
+
+               The only legacy blob displayed is the fw_cfg device revision:
+
+                       /sys/firmware/qemu_fw_cfg/rev
+
+               --- Discoverable fw_cfg blobs by selector key ---
+
+               All discoverable blobs listed in the fw_cfg file directory are
+               displayed as entries named after their unique selector key
+               value, e.g.:
+
+                       /sys/firmware/qemu_fw_cfg/by_key/32
+                       /sys/firmware/qemu_fw_cfg/by_key/33
+                       /sys/firmware/qemu_fw_cfg/by_key/34
+                       ...
+
+               Each such fw_cfg sysfs entry has the following values exported
+               as attributes:
+
+               name    : The 56-byte nul-terminated ASCII string used as the
+                         blob's 'file name' in the fw_cfg directory.
+               size    : The length of the blob, as given in the fw_cfg
+                         directory.
+               key     : The value of the blob's selector key as given in the
+                         fw_cfg directory. This value is the same as used in
+                         the parent directory name.
+               raw     : The raw bytes of the blob, obtained by selecting the
+                         entry via the control register, and reading a number
+                         of bytes equal to the blob size from the data
+                         register.
index 49a3a1185bb607ed45297fe4dea5ff2c6344f37f..5130f74ae3bd87d7c32b1f13af5bc78ddfdfa6be 100644 (file)
@@ -161,6 +161,25 @@ config RASPBERRYPI_FIRMWARE
          This option enables support for communicating with the firmware on the
          Raspberry Pi.
 
+config FW_CFG_SYSFS
+       tristate "QEMU fw_cfg device support in sysfs"
+       depends on SYSFS && (ARM || ARM64 || PPC_PMAC || SPARC || X86)
+       default n
+       help
+         Say Y or M here to enable the exporting of the QEMU firmware
+         configuration (fw_cfg) file entries via sysfs. Entries are
+         found under /sys/firmware/fw_cfg when this option is enabled
+         and loaded.
+
+config FW_CFG_SYSFS_CMDLINE
+       bool "QEMU fw_cfg device parameter parsing"
+       depends on FW_CFG_SYSFS
+       help
+         Allow the qemu_fw_cfg device to be initialized via the kernel
+         command line or using a module parameter.
+         WARNING: Using incorrect parameters (base address in particular)
+         may crash your system.
+
 config QCOM_SCM
        bool
        depends on ARM || ARM64
index 48dd4175297e6cb24151fab67e4c822c940ddf5c..474bada56fcdcd2819afefe5e94e3cb0e191f10c 100644 (file)
@@ -14,6 +14,7 @@ obj-$(CONFIG_ISCSI_IBFT_FIND) += iscsi_ibft_find.o
 obj-$(CONFIG_ISCSI_IBFT)       += iscsi_ibft.o
 obj-$(CONFIG_FIRMWARE_MEMMAP)  += memmap.o
 obj-$(CONFIG_RASPBERRYPI_FIRMWARE) += raspberrypi.o
+obj-$(CONFIG_FW_CFG_SYSFS)     += qemu_fw_cfg.o
 obj-$(CONFIG_QCOM_SCM)         += qcom_scm.o
 obj-$(CONFIG_QCOM_SCM_64)      += qcom_scm-64.o
 obj-$(CONFIG_QCOM_SCM_32)      += qcom_scm-32.o
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
new file mode 100644 (file)
index 0000000..83e8a5c
--- /dev/null
@@ -0,0 +1,648 @@
+/*
+ * drivers/firmware/qemu_fw_cfg.c
+ *
+ * Copyright 2015 Carnegie Mellon University
+ *
+ * Expose entries from QEMU's firmware configuration (fw_cfg) device in
+ * sysfs (read-only, under "/sys/firmware/qemu_fw_cfg/...").
+ *
+ * The fw_cfg device may be instantiated via either an ACPI node (on x86
+ * and select subsets of aarch64), a Device Tree node (on arm), or using
+ * a kernel module (or command line) parameter with the following syntax:
+ *
+ *      [fw_cfg.]ioport=<size>@<base>[:<ctrl_off>:<data_off>]
+ * or
+ *      [fw_cfg.]mmio=<size>@<base>[:<ctrl_off>:<data_off>]
+ *
+ * where:
+ *      <size>     := size of ioport or mmio range
+ *      <base>     := physical base address of ioport or mmio range
+ *      <ctrl_off> := (optional) offset of control register
+ *      <data_off> := (optional) offset of data register
+ *
+ * e.g.:
+ *      fw_cfg.ioport=2@0x510:0:1              (the default on x86)
+ * or
+ *      fw_cfg.mmio=0xA@0x9020000:8:0          (the default on arm)
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/acpi.h>
+#include <linux/slab.h>
+#include <linux/io.h>
+#include <linux/ioport.h>
+
+MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>");
+MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
+MODULE_LICENSE("GPL");
+
+/* selector key values for "well-known" fw_cfg entries */
+#define FW_CFG_SIGNATURE  0x00
+#define FW_CFG_ID         0x01
+#define FW_CFG_FILE_DIR   0x19
+
+/* size in bytes of fw_cfg signature */
+#define FW_CFG_SIG_SIZE 4
+
+/* fw_cfg "file name" is up to 56 characters (including terminating nul) */
+#define FW_CFG_MAX_FILE_PATH 56
+
+/* fw_cfg file directory entry type */
+struct fw_cfg_file {
+       u32 size;
+       u16 select;
+       u16 reserved;
+       char name[FW_CFG_MAX_FILE_PATH];
+};
+
+/* fw_cfg device i/o register addresses */
+static bool fw_cfg_is_mmio;
+static phys_addr_t fw_cfg_p_base;
+static resource_size_t fw_cfg_p_size;
+static void __iomem *fw_cfg_dev_base;
+static void __iomem *fw_cfg_reg_ctrl;
+static void __iomem *fw_cfg_reg_data;
+
+/* atomic access to fw_cfg device (potentially slow i/o, so using mutex) */
+static DEFINE_MUTEX(fw_cfg_dev_lock);
+
+/* pick appropriate endianness for selector key */
+static inline u16 fw_cfg_sel_endianness(u16 key)
+{
+       return fw_cfg_is_mmio ? cpu_to_be16(key) : cpu_to_le16(key);
+}
+
+/* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
+static inline void fw_cfg_read_blob(u16 key,
+                                   void *buf, loff_t pos, size_t count)
+{
+       mutex_lock(&fw_cfg_dev_lock);
+       iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
+       while (pos-- > 0)
+               ioread8(fw_cfg_reg_data);
+       ioread8_rep(fw_cfg_reg_data, buf, count);
+       mutex_unlock(&fw_cfg_dev_lock);
+}
+
+/* clean up fw_cfg device i/o */
+static void fw_cfg_io_cleanup(void)
+{
+       if (fw_cfg_is_mmio) {
+               iounmap(fw_cfg_dev_base);
+               release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
+       } else {
+               ioport_unmap(fw_cfg_dev_base);
+               release_region(fw_cfg_p_base, fw_cfg_p_size);
+       }
+}
+
+/* arch-specific ctrl & data register offsets are not available in ACPI, DT */
+#if !(defined(FW_CFG_CTRL_OFF) && defined(FW_CTRL_DATA_OFF))
+# if (defined(CONFIG_ARM) || defined(CONFIG_ARM64))
+#  define FW_CFG_CTRL_OFF 0x08
+#  define FW_CFG_DATA_OFF 0x00
+# elif (defined(CONFIG_PPC_PMAC) || defined(CONFIG_SPARC32)) /* ppc/mac,sun4m */
+#  define FW_CFG_CTRL_OFF 0x00
+#  define FW_CFG_DATA_OFF 0x02
+# elif (defined(CONFIG_X86) || defined(CONFIG_SPARC64)) /* x86, sun4u */
+#  define FW_CFG_CTRL_OFF 0x00
+#  define FW_CFG_DATA_OFF 0x01
+# else
+#  warning "QEMU FW_CFG may not be available on this architecture!"
+#  define FW_CFG_CTRL_OFF 0x00
+#  define FW_CFG_DATA_OFF 0x01
+# endif
+#endif
+
+/* initialize fw_cfg device i/o from platform data */
+static int fw_cfg_do_platform_probe(struct platform_device *pdev)
+{
+       char sig[FW_CFG_SIG_SIZE];
+       struct resource *range, *ctrl, *data;
+
+       /* acquire i/o range details */
+       fw_cfg_is_mmio = false;
+       range = platform_get_resource(pdev, IORESOURCE_IO, 0);
+       if (!range) {
+               fw_cfg_is_mmio = true;
+               range = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+               if (!range)
+                       return -EINVAL;
+       }
+       fw_cfg_p_base = range->start;
+       fw_cfg_p_size = resource_size(range);
+
+       if (fw_cfg_is_mmio) {
+               if (!request_mem_region(fw_cfg_p_base,
+                                       fw_cfg_p_size, "fw_cfg_mem"))
+                       return -EBUSY;
+               fw_cfg_dev_base = ioremap(fw_cfg_p_base, fw_cfg_p_size);
+               if (!fw_cfg_dev_base) {
+                       release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
+                       return -EFAULT;
+               }
+       } else {
+               if (!request_region(fw_cfg_p_base,
+                                   fw_cfg_p_size, "fw_cfg_io"))
+                       return -EBUSY;
+               fw_cfg_dev_base = ioport_map(fw_cfg_p_base, fw_cfg_p_size);
+               if (!fw_cfg_dev_base) {
+                       release_region(fw_cfg_p_base, fw_cfg_p_size);
+                       return -EFAULT;
+               }
+       }
+
+       /* were custom register offsets provided (e.g. on the command line)? */
+       ctrl = platform_get_resource_byname(pdev, IORESOURCE_REG, "ctrl");
+       data = platform_get_resource_byname(pdev, IORESOURCE_REG, "data");
+       if (ctrl && data) {
+               fw_cfg_reg_ctrl = fw_cfg_dev_base + ctrl->start;
+               fw_cfg_reg_data = fw_cfg_dev_base + data->start;
+       } else {
+               /* use architecture-specific offsets */
+               fw_cfg_reg_ctrl = fw_cfg_dev_base + FW_CFG_CTRL_OFF;
+               fw_cfg_reg_data = fw_cfg_dev_base + FW_CFG_DATA_OFF;
+       }
+
+       /* verify fw_cfg device signature */
+       fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
+       if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
+               fw_cfg_io_cleanup();
+               return -ENODEV;
+       }
+
+       return 0;
+}
+
+/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
+static u32 fw_cfg_rev;
+
+static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf)
+{
+       return sprintf(buf, "%u\n", fw_cfg_rev);
+}
+
+static const struct {
+       struct attribute attr;
+       ssize_t (*show)(struct kobject *k, struct attribute *a, char *buf);
+} fw_cfg_rev_attr = {
+       .attr = { .name = "rev", .mode = S_IRUSR },
+       .show = fw_cfg_showrev,
+};
+
+/* fw_cfg_sysfs_entry type */
+struct fw_cfg_sysfs_entry {
+       struct kobject kobj;
+       struct fw_cfg_file f;
+       struct list_head list;
+};
+
+/* get fw_cfg_sysfs_entry from kobject member */
+static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj)
+{
+       return container_of(kobj, struct fw_cfg_sysfs_entry, kobj);
+}
+
+/* fw_cfg_sysfs_attribute type */
+struct fw_cfg_sysfs_attribute {
+       struct attribute attr;
+       ssize_t (*show)(struct fw_cfg_sysfs_entry *entry, char *buf);
+};
+
+/* get fw_cfg_sysfs_attribute from attribute member */
+static inline struct fw_cfg_sysfs_attribute *to_attr(struct attribute *attr)
+{
+       return container_of(attr, struct fw_cfg_sysfs_attribute, attr);
+}
+
+/* global cache of fw_cfg_sysfs_entry objects */
+static LIST_HEAD(fw_cfg_entry_cache);
+
+/* kobjects removed lazily by kernel, mutual exclusion needed */
+static DEFINE_SPINLOCK(fw_cfg_cache_lock);
+
+static inline void fw_cfg_sysfs_cache_enlist(struct fw_cfg_sysfs_entry *entry)
+{
+       spin_lock(&fw_cfg_cache_lock);
+       list_add_tail(&entry->list, &fw_cfg_entry_cache);
+       spin_unlock(&fw_cfg_cache_lock);
+}
+
+static inline void fw_cfg_sysfs_cache_delist(struct fw_cfg_sysfs_entry *entry)
+{
+       spin_lock(&fw_cfg_cache_lock);
+       list_del(&entry->list);
+       spin_unlock(&fw_cfg_cache_lock);
+}
+
+static void fw_cfg_sysfs_cache_cleanup(void)
+{
+       struct fw_cfg_sysfs_entry *entry, *next;
+
+       list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) {
+               /* will end up invoking fw_cfg_sysfs_cache_delist()
+                * via each object's release() method (i.e. destructor)
+                */
+               kobject_put(&entry->kobj);
+       }
+}
+
+/* default_attrs: per-entry attributes and show methods */
+
+#define FW_CFG_SYSFS_ATTR(_attr) \
+struct fw_cfg_sysfs_attribute fw_cfg_sysfs_attr_##_attr = { \
+       .attr = { .name = __stringify(_attr), .mode = S_IRUSR }, \
+       .show = fw_cfg_sysfs_show_##_attr, \
+}
+
+static ssize_t fw_cfg_sysfs_show_size(struct fw_cfg_sysfs_entry *e, char *buf)
+{
+       return sprintf(buf, "%u\n", e->f.size);
+}
+
+static ssize_t fw_cfg_sysfs_show_key(struct fw_cfg_sysfs_entry *e, char *buf)
+{
+       return sprintf(buf, "%u\n", e->f.select);
+}
+
+static ssize_t fw_cfg_sysfs_show_name(struct fw_cfg_sysfs_entry *e, char *buf)
+{
+       return sprintf(buf, "%s\n", e->f.name);
+}
+
+static FW_CFG_SYSFS_ATTR(size);
+static FW_CFG_SYSFS_ATTR(key);
+static FW_CFG_SYSFS_ATTR(name);
+
+static struct attribute *fw_cfg_sysfs_entry_attrs[] = {
+       &fw_cfg_sysfs_attr_size.attr,
+       &fw_cfg_sysfs_attr_key.attr,
+       &fw_cfg_sysfs_attr_name.attr,
+       NULL,
+};
+
+/* sysfs_ops: find fw_cfg_[entry, attribute] and call appropriate show method */
+static ssize_t fw_cfg_sysfs_attr_show(struct kobject *kobj, struct attribute *a,
+                                     char *buf)
+{
+       struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
+       struct fw_cfg_sysfs_attribute *attr = to_attr(a);
+
+       return attr->show(entry, buf);
+}
+
+static const struct sysfs_ops fw_cfg_sysfs_attr_ops = {
+       .show = fw_cfg_sysfs_attr_show,
+};
+
+/* release: destructor, to be called via kobject_put() */
+static void fw_cfg_sysfs_release_entry(struct kobject *kobj)
+{
+       struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
+
+       fw_cfg_sysfs_cache_delist(entry);
+       kfree(entry);
+}
+
+/* kobj_type: ties together all properties required to register an entry */
+static struct kobj_type fw_cfg_sysfs_entry_ktype = {
+       .default_attrs = fw_cfg_sysfs_entry_attrs,
+       .sysfs_ops = &fw_cfg_sysfs_attr_ops,
+       .release = fw_cfg_sysfs_release_entry,
+};
+
+/* raw-read method and attribute */
+static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
+                                    struct bin_attribute *bin_attr,
+                                    char *buf, loff_t pos, size_t count)
+{
+       struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
+
+       if (pos > entry->f.size)
+               return -EINVAL;
+
+       if (count > entry->f.size - pos)
+               count = entry->f.size - pos;
+
+       fw_cfg_read_blob(entry->f.select, buf, pos, count);
+       return count;
+}
+
+static struct bin_attribute fw_cfg_sysfs_attr_raw = {
+       .attr = { .name = "raw", .mode = S_IRUSR },
+       .read = fw_cfg_sysfs_read_raw,
+};
+
+/* kobjects representing top-level and by_key folders */
+static struct kobject *fw_cfg_top_ko;
+static struct kobject *fw_cfg_sel_ko;
+
+/* register an individual fw_cfg file */
+static int fw_cfg_register_file(const struct fw_cfg_file *f)
+{
+       int err;
+       struct fw_cfg_sysfs_entry *entry;
+
+       /* allocate new entry */
+       entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+       if (!entry)
+               return -ENOMEM;
+
+       /* set file entry information */
+       memcpy(&entry->f, f, sizeof(struct fw_cfg_file));
+
+       /* register entry under "/sys/firmware/qemu_fw_cfg/by_key/" */
+       err = kobject_init_and_add(&entry->kobj, &fw_cfg_sysfs_entry_ktype,
+                                  fw_cfg_sel_ko, "%d", entry->f.select);
+       if (err)
+               goto err_register;
+
+       /* add raw binary content access */
+       err = sysfs_create_bin_file(&entry->kobj, &fw_cfg_sysfs_attr_raw);
+       if (err)
+               goto err_add_raw;
+
+       /* success, add entry to global cache */
+       fw_cfg_sysfs_cache_enlist(entry);
+       return 0;
+
+err_add_raw:
+       kobject_del(&entry->kobj);
+err_register:
+       kfree(entry);
+       return err;
+}
+
+/* iterate over all fw_cfg directory entries, registering each one */
+static int fw_cfg_register_dir_entries(void)
+{
+       int ret = 0;
+       u32 count, i;
+       struct fw_cfg_file *dir;
+       size_t dir_size;
+
+       fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count));
+       count = be32_to_cpu(count);
+       dir_size = count * sizeof(struct fw_cfg_file);
+
+       dir = kmalloc(dir_size, GFP_KERNEL);
+       if (!dir)
+               return -ENOMEM;
+
+       fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size);
+
+       for (i = 0; i < count; i++) {
+               dir[i].size = be32_to_cpu(dir[i].size);
+               dir[i].select = be16_to_cpu(dir[i].select);
+               ret = fw_cfg_register_file(&dir[i]);
+               if (ret)
+                       break;
+       }
+
+       kfree(dir);
+       return ret;
+}
+
+/* unregister top-level or by_key folder */
+static inline void fw_cfg_kobj_cleanup(struct kobject *kobj)
+{
+       kobject_del(kobj);
+       kobject_put(kobj);
+}
+
+static int fw_cfg_sysfs_probe(struct platform_device *pdev)
+{
+       int err;
+
+       /* NOTE: If we supported multiple fw_cfg devices, we'd first create
+        * a subdirectory named after e.g. pdev->id, then hang per-device
+        * by_key subdirectories underneath it. However, only
+        * one fw_cfg device exist system-wide, so if one was already found
+        * earlier, we might as well stop here.
+        */
+       if (fw_cfg_sel_ko)
+               return -EBUSY;
+
+       /* create by_key subdirectory of /sys/firmware/qemu_fw_cfg/ */
+       err = -ENOMEM;
+       fw_cfg_sel_ko = kobject_create_and_add("by_key", fw_cfg_top_ko);
+       if (!fw_cfg_sel_ko)
+               goto err_sel;
+
+       /* initialize fw_cfg device i/o from platform data */
+       err = fw_cfg_do_platform_probe(pdev);
+       if (err)
+               goto err_probe;
+
+       /* get revision number, add matching top-level attribute */
+       fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev));
+       fw_cfg_rev = le32_to_cpu(fw_cfg_rev);
+       err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
+       if (err)
+               goto err_rev;
+
+       /* process fw_cfg file directory entry, registering each file */
+       err = fw_cfg_register_dir_entries();
+       if (err)
+               goto err_dir;
+
+       /* success */
+       pr_debug("fw_cfg: loaded.\n");
+       return 0;
+
+err_dir:
+       fw_cfg_sysfs_cache_cleanup();
+       sysfs_remove_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
+err_rev:
+       fw_cfg_io_cleanup();
+err_probe:
+       fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
+err_sel:
+       return err;
+}
+
+static int fw_cfg_sysfs_remove(struct platform_device *pdev)
+{
+       pr_debug("fw_cfg: unloading.\n");
+       fw_cfg_sysfs_cache_cleanup();
+       fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
+       fw_cfg_io_cleanup();
+       return 0;
+}
+
+static const struct of_device_id fw_cfg_sysfs_mmio_match[] = {
+       { .compatible = "qemu,fw-cfg-mmio", },
+       {},
+};
+MODULE_DEVICE_TABLE(of, fw_cfg_sysfs_mmio_match);
+
+#ifdef CONFIG_ACPI
+static const struct acpi_device_id fw_cfg_sysfs_acpi_match[] = {
+       { "QEMU0002", },
+       {},
+};
+MODULE_DEVICE_TABLE(acpi, fw_cfg_sysfs_acpi_match);
+#endif
+
+static struct platform_driver fw_cfg_sysfs_driver = {
+       .probe = fw_cfg_sysfs_probe,
+       .remove = fw_cfg_sysfs_remove,
+       .driver = {
+               .name = "fw_cfg",
+               .of_match_table = fw_cfg_sysfs_mmio_match,
+               .acpi_match_table = ACPI_PTR(fw_cfg_sysfs_acpi_match),
+       },
+};
+
+#ifdef CONFIG_FW_CFG_SYSFS_CMDLINE
+
+static struct platform_device *fw_cfg_cmdline_dev;
+
+/* this probably belongs in e.g. include/linux/types.h,
+ * but right now we are the only ones doing it...
+ */
+#ifdef CONFIG_PHYS_ADDR_T_64BIT
+#define __PHYS_ADDR_PREFIX "ll"
+#else
+#define __PHYS_ADDR_PREFIX ""
+#endif
+
+/* use special scanf/printf modifier for phys_addr_t, resource_size_t */
+#define PH_ADDR_SCAN_FMT "@%" __PHYS_ADDR_PREFIX "i%n" \
+                        ":%" __PHYS_ADDR_PREFIX "i" \
+                        ":%" __PHYS_ADDR_PREFIX "i%n"
+
+#define PH_ADDR_PR_1_FMT "0x%" __PHYS_ADDR_PREFIX "x@" \
+                        "0x%" __PHYS_ADDR_PREFIX "x"
+
+#define PH_ADDR_PR_3_FMT PH_ADDR_PR_1_FMT \
+                        ":%" __PHYS_ADDR_PREFIX "u" \
+                        ":%" __PHYS_ADDR_PREFIX "u"
+
+static int fw_cfg_cmdline_set(const char *arg, const struct kernel_param *kp)
+{
+       struct resource res[3] = {};
+       char *str;
+       phys_addr_t base;
+       resource_size_t size, ctrl_off, data_off;
+       int processed, consumed = 0;
+
+       /* only one fw_cfg device can exist system-wide, so if one
+        * was processed on the command line already, we might as
+        * well stop here.
+        */
+       if (fw_cfg_cmdline_dev) {
+               /* avoid leaking previously registered device */
+               platform_device_unregister(fw_cfg_cmdline_dev);
+               return -EINVAL;
+       }
+
+       /* consume "<size>" portion of command line argument */
+       size = memparse(arg, &str);
+
+       /* get "@<base>[:<ctrl_off>:<data_off>]" chunks */
+       processed = sscanf(str, PH_ADDR_SCAN_FMT,
+                          &base, &consumed,
+                          &ctrl_off, &data_off, &consumed);
+
+       /* sscanf() must process precisely 1 or 3 chunks:
+        * <base> is mandatory, optionally followed by <ctrl_off>
+        * and <data_off>;
+        * there must be no extra characters after the last chunk,
+        * so str[consumed] must be '\0'.
+        */
+       if (str[consumed] ||
+           (processed != 1 && processed != 3))
+               return -EINVAL;
+
+       res[0].start = base;
+       res[0].end = base + size - 1;
+       res[0].flags = !strcmp(kp->name, "mmio") ? IORESOURCE_MEM :
+                                                  IORESOURCE_IO;
+
+       /* insert register offsets, if provided */
+       if (processed > 1) {
+               res[1].name = "ctrl";
+               res[1].start = ctrl_off;
+               res[1].flags = IORESOURCE_REG;
+               res[2].name = "data";
+               res[2].start = data_off;
+               res[2].flags = IORESOURCE_REG;
+       }
+
+       /* "processed" happens to nicely match the number of resources
+        * we need to pass in to this platform device.
+        */
+       fw_cfg_cmdline_dev = platform_device_register_simple("fw_cfg",
+                                       PLATFORM_DEVID_NONE, res, processed);
+       if (IS_ERR(fw_cfg_cmdline_dev))
+               return PTR_ERR(fw_cfg_cmdline_dev);
+
+       return 0;
+}
+
+static int fw_cfg_cmdline_get(char *buf, const struct kernel_param *kp)
+{
+       /* stay silent if device was not configured via the command
+        * line, or if the parameter name (ioport/mmio) doesn't match
+        * the device setting
+        */
+       if (!fw_cfg_cmdline_dev ||
+           (!strcmp(kp->name, "mmio") ^
+            (fw_cfg_cmdline_dev->resource[0].flags == IORESOURCE_MEM)))
+               return 0;
+
+       switch (fw_cfg_cmdline_dev->num_resources) {
+       case 1:
+               return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_1_FMT,
+                               resource_size(&fw_cfg_cmdline_dev->resource[0]),
+                               fw_cfg_cmdline_dev->resource[0].start);
+       case 3:
+               return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_3_FMT,
+                               resource_size(&fw_cfg_cmdline_dev->resource[0]),
+                               fw_cfg_cmdline_dev->resource[0].start,
+                               fw_cfg_cmdline_dev->resource[1].start,
+                               fw_cfg_cmdline_dev->resource[2].start);
+       }
+
+       /* Should never get here */
+       WARN(1, "Unexpected number of resources: %d\n",
+               fw_cfg_cmdline_dev->num_resources);
+       return 0;
+}
+
+static const struct kernel_param_ops fw_cfg_cmdline_param_ops = {
+       .set = fw_cfg_cmdline_set,
+       .get = fw_cfg_cmdline_get,
+};
+
+device_param_cb(ioport, &fw_cfg_cmdline_param_ops, NULL, S_IRUSR);
+device_param_cb(mmio, &fw_cfg_cmdline_param_ops, NULL, S_IRUSR);
+
+#endif /* CONFIG_FW_CFG_SYSFS_CMDLINE */
+
+static int __init fw_cfg_sysfs_init(void)
+{
+       /* create /sys/firmware/qemu_fw_cfg/ top level directory */
+       fw_cfg_top_ko = kobject_create_and_add("qemu_fw_cfg", firmware_kobj);
+       if (!fw_cfg_top_ko)
+               return -ENOMEM;
+
+       return platform_driver_register(&fw_cfg_sysfs_driver);
+}
+
+static void __exit fw_cfg_sysfs_exit(void)
+{
+       platform_driver_unregister(&fw_cfg_sysfs_driver);
+
+#ifdef CONFIG_FW_CFG_SYSFS_CMDLINE
+       platform_device_unregister(fw_cfg_cmdline_dev);
+#endif
+
+       /* clean up /sys/firmware/qemu_fw_cfg/ */
+       fw_cfg_kobj_cleanup(fw_cfg_top_ko);
+}
+
+module_init(fw_cfg_sysfs_init);
+module_exit(fw_cfg_sysfs_exit);