Re: [RFT PATCH v3 12/27] of/address: Add infrastructure to declare MMIO as non-posted

[Arnd Bergmann]

On Thu, Mar 11, 2021 at 5:10 PM Rob Herring <robh@xxxxxxxxxx> wrote:
> On Thu, Mar 11, 2021 at 2:12 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> > On Wed, Mar 10, 2021 at 6:01 PM Rob Herring <robh@xxxxxxxxxx> wrote:
> > Ok, makes sense.
> >
> > Conceptually, I'd like to then see a check that verifies that the
> > property is only set for nodes whose parent also has it set, since
> > that is how AXI defines it: A bus can wait for the ack from its
> > child node, or it can acknowledge the write to its parent early.
> > However, this breaks down as soon as a bus does the early ack:
> > all its children by definition use posted writes (as seen by the
> > CPU), even if they wait for stores that come from other masters.
> >
> > Does this make sense to you?
>
> BTW, I don't think it's clear in this thread, but the current
> definition proposed for the spec[1] and schema is 'nonposted-mmio' is
> specific to 'simple-bus'. I like this restriction and we can expand
> where 'nonposted-mmio' is allowed later if needed.

That sounds ok, as long as we can express everything for the mac
at the moment. Do we need to explicitly add a description to allow
the property in the root node in addition to simple-bus to be able
to enforce the rule about parent buses also having it?

       Arnd