linux-kernel - Re: [RFC/PATCH v4 1/4] Document nexus nodes/specifier remapping

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Message-ID: <CAL_Jsq+qRm=iAhQz6Ro3SAU45JEK8KNWpRBcXuRt47r8ncYYwQ@mail.gmail.com>
Date:   Mon, 18 Sep 2017 12:44:38 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Stephen Boyd <stephen.boyd@...aro.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        "devicetree-spec@...r.kernel.org" <devicetree-spec@...r.kernel.org>
Subject: Re: [RFC/PATCH v4 1/4] Document nexus nodes/specifier remapping

On Fri, Aug 11, 2017 at 10:42 AM, Stephen Boyd <stephen.boyd@...aro.org> wrote:
> Document the generic nexus node properties. This can be used by
> any specifier that conforms to #<specifier>-cells where they
> want to support remapping phandle lists through nexus nodes. This
> is similar to interrupt remapping, but slightly different because
> we don't consider unit addresses when doing mappings. This is
> mostly a copy/paste of the interrupt specification, with the unit
> address parts removed and generalized to any specifier. There's
> also the addition of a pass through mechanism to make things more
> compact if desired in the mapping table.

Sorry for the slow response.

I'm still wondering how/if we can merge interrupts as part of this
(both the spec and parsing implementation). Could we simply require
that #address-cells is 0 or do we even need this distinction? If the
usecase is connectors, then we should typically be able to set
#address-cells to 0. Perhaps you could have a custom PCI connector
with additional signals and the slot/connector node would have the PCI
address. In this case, we would have #address-cells, but having them
and ignoring the address cells via the mask would still work.

Also, I don't see any issue if we allow the -map-pass-thru property
for interrupts.

>
> Signed-off-by: Stephen Boyd <stephen.boyd@...aro.org>
> ---
>
> I still need to write the blurb about what this is all about, but
> I wanted to send this out now to get early feedback. Some starting
> points:
>
>  1) Replace child/parent with incoming/outgoing everywhere?

Parent/child is more common, so I think that's fine.

>
>  2) Make a pretty picture to describe remapping phandle+specifiers
>     similar to the interrupt hierarchy diagram?

Pictures are always nice, but I don't think required.

>
>  3) Come up with some better name than <specifier>? Kernel-doc uses <list>
>     but I'm not sure that's any better.

specifier seems fine to me.

Rob