platform/x86: dell-smbios: Add a sysfs interface for SMBIOS tokens

Currently userspace tools can access system tokens via the dcdbas
kernel module and a SMI call that will cause the platform to execute
SMM code.

With a goal in mind of deprecating the dcdbas kernel module a different
method for accessing these tokens from userspace needs to be created.

This is intentionally marked to only be readable as a process with
CAP_SYS_ADMIN as it can contain sensitive information about the
platform's configuration.

While adding this interface I found that some tokens are duplicated.
These need to be ignored from sysfs to avoid duplicate files.

MAINTAINERS was missing for this driver.  Add myself and Pali to
maintainers list for it.

Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Reviewed-by: Edward O'Callaghan <quasisec@google.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-platform-dell-smbios b/Documentation/ABI/testing/sysfs-platform-dell-smbios
new file mode 100644
index 000000000000..205d3b6361e0
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-platform-dell-smbios
@@ -0,0 +1,21 @@
+What:		/sys/devices/platform/<platform>/tokens/*
+Date:		November 2017
+KernelVersion:	4.15
+Contact:	"Mario Limonciello" <mario.limonciello@dell.com>
+Description:
+		A read-only description of Dell platform tokens
+		available on the machine.
+
+		Each token attribute is available as a pair of
+		sysfs attributes readable by a process with
+		CAP_SYS_ADMIN.
+
+		For example the token ID "5" would be available
+		as the following attributes:
+
+		0005_location
+		0005_value
+
+		Tokens will vary from machine to machine, and
+		only tokens available on that machine will be
+		displayed.