[RFC v1 0/4] ipmi_bmc: framework for IPMI on BMCs

[Brendan Higgins <brendanhiggins@google.com>]

This introduces a framework for implementing the BMC side of the IPMI protocol,
roughly mirroring the host side OpenIPMI framework; it attempts to abstract away
hardware interfaces, such as Block Transfer interface hardware implementations
from IPMI command handlers.

It does this by implementing the traditional driver model of a bus with devices;
however, in this case a struct ipmi_bmc_bus represents a hardware interface,
where a struct ipmi_bmc_device represents a handler. A handler filters messages
by registering a function which returns whether a given message matches the
handler; it also has the concept of a default handler which is forwarded all
messages which are not matched by some other interface.

In this patchset, we introduce an example of a default handler: a misc device
file interface which implements the same interface as the the device file
interface used by the Aspeed BT driver.

Currently, OpenBMC handles all IPMI message routing and handling in userland;
the existing drivers simply provide a file interface for the hardware on the
device. In this patchset, we propose a common file interface to be shared by all
IPMI hardware interfaces, but also a framework for implementing handlers at the
kernel level, similar to how the existing OpenIPMI framework supports both
kernel users, as well as misc device file interface.

This patchset depends on the "ipmi: bt-i2c: added IPMI Block Transfer over I2C"
patchset, which can be found here:
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1461960.html
However, I can fix this if desired.

Tested on the AST2500 EVB.