[PATCH linux dev-4.10] drivers/fsi: Remove scan from master registration

Patrick Williams patrick at stwcx.xyz
Sat Jul 29 01:14:05 AEST 2017

On Fri, Jul 28, 2017 at 09:57:23AM -0500, Eddie James wrote:
> 2) FSI operations while the host is booting can cause FSI failures. 
> Since we don't know the state of the host while booting the BMC, it's 
> generally not safe to do FSI ops as we may disrupt the host.

From my perspective this is especially bad because it would only surface
in specific timing conditions.  The FSI bus is, by the system
architecture, under the control of the Host for a period during the
boot.  Both FSP in the past and BMC now are required to stay clear of
the FSI bus when the Host owns it.  If we do not, it can, in the best
case, cause unexpected FSI errors for the Host resulting in extra parts
being "guarded" and, in the worst case, cause silent corruption of
chip initialization registers leading to an unknown data integrity
problem at some future point.

When the BMC reboots, the kernel cannot know the ownership state of the
FSI bus, so we should assume it is un-owned and not do any activity
until userspace has had time to "assess the situation".

Patrick Williams
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