platform/x86: dell-smbios-wmi: introduce userspace interface

It's important for the driver to provide a R/W ioctl to ensure that
two competing userspace processes don't race to provide or read each
others data.

This userspace character device will be used to perform SMBIOS calls
from any applications.

It provides an ioctl that will allow passing the WMI calling
interface buffer between userspace and kernel space.

This character device is intended to deprecate the dcdbas kernel module
and the interface that it provides to userspace.

To perform an SMBIOS IOCTL call using the character device userspace will
perform a read() on the the character device.  The WMI bus will provide
a u64 variable containing the necessary size of the IOCTL buffer.

The API for interacting with this interface is defined in documentation
as well as the WMI uapi header provides the format of the structures.

Not all userspace requests will be accepted.  The dell-smbios filtering
functionality will be used to prevent access to certain tokens and calls.

All whitelisted commands and tokens are now shared out to userspace so
applications don't need to define them in their own headers.

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, 41 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/dell-smbios-wmi b/Documentation/ABI/testing/dell-smbios-wmi
new file mode 100644
index 000000000000..fc919ce16008
--- /dev/null
+++ b/Documentation/ABI/testing/dell-smbios-wmi
@@ -0,0 +1,41 @@
+What:		/dev/wmi/dell-smbios
+Date:		November 2017
+KernelVersion:	4.15
+Contact:	"Mario Limonciello" <mario.limonciello@dell.com>
+Description:
+		Perform SMBIOS calls on supported Dell machines.
+		through the Dell ACPI-WMI interface.
+
+		IOCTL's and buffer formats are defined in:
+		<uapi/linux/wmi.h>
+
+		1) To perform an SMBIOS call from userspace, you'll need to
+		first determine the minimum size of the calling interface
+		buffer for your machine.
+		Platforms that contain larger buffers can return larger
+		objects from the system firmware.
+		Commonly this size is either 4k or 32k.
+
+		To determine the size of the buffer read() a u64 dword from
+		the WMI character device /dev/wmi/dell-smbios.
+
+		2) After you've determined the minimum size of the calling
+		interface buffer, you can allocate a structure that represents
+		the structure documented above.
+
+		3) In the 'length' object store the size of the buffer you
+		determined above and allocated.
+
+		4) In this buffer object, prepare as necessary for the SMBIOS
+		call you're interested in.  Typically SMBIOS buffers have
+		"class", "select", and "input" defined to values that coincide
+		with the data you are interested in.
+		Documenting class/select/input values is outside of the scope
+		of this documentation. Check with the libsmbios project for
+		further documentation on these values.
+
+		6) Run the call by using ioctl() as described in the header.
+
+		7) The output will be returned in the buffer object.
+
+		8) Be sure to free up your allocated object.