Re: [Qemu-devel] [PATCH v8 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

[Michael S. Tsirkin]

On Thu, Jan 28, 2016 at 09:23:11AM -0500, Gabriel L. Somlo wrote:
> From: Gabriel Somlo <address@hidden>
> 
> 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 <address@hidden>
> ---
>  .../ABI/testing/sysfs-firmware-qemu_fw_cfg         |  58 ++
>  drivers/firmware/Kconfig                           |  19 +
>  drivers/firmware/Makefile                          |   1 +
>  drivers/firmware/qemu_fw_cfg.c                     | 648 
> +++++++++++++++++++++
>  4 files changed, 726 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
>  create mode 100644 drivers/firmware/qemu_fw_cfg.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg 
> b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
> new file mode 100644
> index 0000000..e9e58d4
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
> @@ -0,0 +1,58 @@
> +What:                /sys/firmware/qemu_fw_cfg/
> +Date:                August 2015
> +Contact:     Gabriel Somlo <address@hidden>
> +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.
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index 49a3a11..5130f74 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -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
> diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
> index 48dd417..474bada 100644
> --- a/drivers/firmware/Makefile
> +++ b/drivers/firmware/Makefile
> @@ -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
> index 0000000..83e8a5c
> --- /dev/null
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -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.:
> + *      address@hidden:0:1           (the default on x86)
> + * or
> + *      address@hidden: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 <address@hidden>");
> +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);
> +}

This locking is not enough I think: ACPI might be
accessing FW CFG meanwhile, and assuming it's
the only owner.

I think that on systems that support ACPI,
it would be better to use an ACPI interface
to read blobs, instead of poking on _CRS and banging on registers directly.

This will also make it easier to extend the interface,
and support DMA.



> +
> +/* 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 
> */

So for all arches which support ACPI, I think this driver
should just rely on ACPI.

> +#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

Better not try hacks like this, they are hard
to support down the road. Please only list what is tested and
actually exposed by QEMU.


> +# 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);
> -- 
> 2.4.3