On Fri, Feb 17, 2017 at 05:44:57PM +1100, Benjamin Herrenschmidt wrote: > On Fri, 2017-02-17 at 14:28 +1100, Cyril Bur wrote: > > In order to manage server systems, there is typically another > > processor > > known as a BMC (Baseboard Management Controller) which is responsible > > for powering the server and other various elements, sometimes fans, > > often the system flash. > > .../... > > > It is important to note that due to the way the Aspeed chip lets the > > kernel configure the mapping between host LPC addresses and BMC ram > > addresses the offset within the window must be a multiple of size. > > Not doing so will fragment the accessible space rather than simply > > moving 'zero' upwards. This is caused by the nature of HICR8 being a > > mask and the way host LPC addresses are translated. > > > > Signed-off-by: Cyril Bur <cyril...@gmail.com> > > Reviewed-by: Benjamin Herrenschmidt <b...@kernel.crashing.org> > > Greg, quick Q for you: > > We will need to also add a mechanism to poke at a few registers > in the same LPC controllers from userspace. > > Mostly those are "scratch" registers that the BMC is supposed to set to > specific values to indicates features it supports etc... (or to enable > the host BIOS to run in some kind of verbose debug mode). > > Think of it as a communication channel between the BMC and the BIOS > running on the host. > > The BMC userspace needs to set them to various platform specific > values as appropriate for a given vendor/system (userspace policy > from the BMC perspective) during boot and/or change them as the result > of some user actions (enable debug mode) etc... > > The question here is read/write or sysfs files attached to the > sysfs node ? > > The former means userspace needs to "seek" to the right magic > offset to write to one of them which is non-trivial to do from > simple shell scripts but is a more natural interface. > > It also means the owner/permissions of the /dev entry as set > by uboot apply which can be nice. > > The latter can expose each register by its name which provides > a nice way to echo in/out of them from a shell script. > > The drawback is that pretty much restricts access to root. > > What do you recommend ?
That wasn't a quick question :) I really have no idea, sorry, try some things out and see what seems to work. greg k-h
