[PATCH v2 1/3] ARM: l2c: add pl310-no-sideband option

[Chris Brandt]

On Wednesday, February 15, 2017, Rob Herring wrote:
> On Tue, Feb 07, 2017 at 12:09:27PM -0500, Chris Brandt wrote:
> > If a PL310 is added to a system, but the sideband signals are not
> > connected, some Cortex A9 optimizations cannot be used. In particular,
> > enabling Full Line Zeros in the CA9 without sidebands connected will
> > crash the system since the CA9 will expect the L2C to perform
> > operations, yet the L2C never gets the commands.
> 
> I assume you are talking about just the AxUSER signals, not the AxCACHE
> signals too. That would be really broken. IIRC, the other AxUSER signals
> are just hints and no connection would not be a problem. This is the only
> one that requires coordination with enabling/disabling in the core.

Yes, just the AxUSER, hence none of the "2.5.5 Cortex-A9 optimizations" work.
Well, except "Store buffer device limitation" because that doesn't use sideband
signals.

Like you mentioned, having 'Early BRESP' enabled but not used doesn't hurt
anything. I was just blocking that so it would print out that it was enabled
and give users false hope (not that they are looking at the boot log that closely
anyway.) FLZ is the killer.


> I think this should follow existing feature properties and explicitly
> disable the specific properties rather than have this indirection.

I can change the code to:

  "arm,early-bresp-disable"
  "arm,fill-line-zero-disable"


As I said, blocking BRESP is only for keeping the log message from coming out.
If it's preferred to not block anything that doesn't break anything, I can just
add "arm,fill-line-zero-disable" only. Just let me know.


Chris