tree 1940f23753ba276b22ae4b3fd654bb6e61812f24
parent eba19a3b122a39ef2b5dbda49b418a202f78a48d
author Andrew Jeffery <andrew@aj.id.au> 1620697493 +0930
committer Andrew Jeffery <andrew@aj.id.au> 1620705417 +0930

astlpc: Ship udev rules to help with device and driver transition

Currently the OpenBMC kernel has a hacky device driver at
drivers/char/misc/mctp-lpc.c that only works against KCS channel 4 on
Aspeed BMCs. This hacky driver exposes an `mctp0` device node.

The intent is to replace it with one that is slightly less
hacky at drivers/char/ipmi/kcs_bmc_cdev_raw.c[1], though eventually this
too will be replaced by an in-kernel implementation of the entire LPC
MCTP binding.

kcs_bmc_dev_raw.c works against all KCS devices in both Aspeed and
Nuvoton BMC SoCs.

We need to move away from KCS channel 4 on the Aspeed BMCs as the way
the hardware initialises the status bits conflicts with the protocol
definition for the LPC MCTP binding[2].

Kill two birds with one stone by shipping udev rules that accomodate the
new device node names that come with kcs_bmc_dev_raw.c, and symlink them
upon creation to /dev/mctp0 to emulate the original mctp-lpc.c
interface.

[1] https://lore.kernel.org/openbmc/20210510064955.1704652-1-andrew@aj.id.au/T/#me02d9a0e6ce82c9e0602cd615ccdad66d242af87
[2] https://github.com/openbmc/libmctp/blob/eba19a3b122a39ef2b5dbda49b418a202f78a48d/docs/bindings/vendor-ibm-astlpc.md#kcs-status-register-layout

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I21446936cea6c5e4024ec6536ad5983dd360deb2