firmware: introduce sysfs driver for QEMU's fw_cfg device

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>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 49a3a1185bb6..5130f74ae3bd 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