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

Jeremy Kerr jk at ozlabs.org
Mon Jul 31 12:36:04 AEST 2017

Hi Chris,

> Not sure I follow what the FSI GPIO master probe would do if it can't
> access the GPIO itself, assuming we're in blocked mode. Would this
> require a deferred probe of some kind once access is unblocked?

Yes, any state change from blocked to unblocked would need to reinit the
GPIOs, and potentially initiate a scan.

So, if we're initialised in blocked mode, the fsi master gpio driver
would still claim the GPIOs (but not change any of their states),
register with the FSI core, etc, but couldn't start any operations that
require GPIO activity.

> Also, in the existing FSP-2 implementation there is a bit in the FSI
> slave SISC which indicates if OPB if fence by host.  Which I believe is
> set whenever host boot is using the FSI bus.   Possibly we could use
> that info to determine if any FSI accesses past the CFAM slave engines
> are allowed.   This might be racy though since BMC can't control when
> that bit is set and cleared.

OK, I'm confused - are we able to access *some* parts of the FSI bus
(ie, the SISC register in the CFAM) while the host is booting?

But as you say, this might race. It would seem simpler to use the BMC's
knowledge of when the host is booting to decide when the BMC is able to
access the bus.



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