netdev - Re: [PATCH v2 1/4] net: dt-bindings: Document the new Meson8b and GXBB DWMAC bindings

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Date:   Mon, 29 Aug 2016 15:31:12 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-arm-kernel@...ts.infradead.org, mark.rutland@....com,
        devicetree@...r.kernel.org, sboyd@...eaurora.org,
        catalin.marinas@....com, alexandre.torgue@...com,
        khilman@...libre.com, mturquette@...libre.com, will.deacon@....com,
        robh+dt@...nel.org, peppe.cavallaro@...com, carlo@...one.org,
        linux-amlogic@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 1/4] net: dt-bindings: Document the new Meson8b and GXBB DWMAC bindings

On Sunday 28 August 2016, Martin Blumenstingl wrote:
> On Mon, Aug 22, 2016 at 5:25 PM, Arnd Bergmann <arnd@...db.de> wrote:
> > It really depends on the kind of SoC. Some may have a suboptimal
> > binding, on some others there may be a distinct register area that
> > just contains a few additional registers for the dwmac.
> the dwmac PHY configuration registers (2x32bit) on the GXBB SoC are
> part of the "periphs" region/module. This is already defined as
> "simple-bus" in meson-gxbb.dtsi, see [0]
> On Meson8b this is slightly different: there is no specific "periphs"
> region - there the dwmac PHY configuration registers are directly
> located in the cbus region at a slightly different offset than on the
> GXBB SoCs.
> 
> In the future we might need a third memory region because the latest
> reference kernel contains some more PHY configuration registers on
> newer SoCs (GXL = S905X).
> 
> Please let me know if you're OK with the dts definition in it's
> current state - or let me know how you would like to change it.
> 
> PS: I will re-send the patches in a v3 in a few minutes because that
> fixes a bug during module unload.

I don't really see a good way to describe this hardware then. If it
was only the first case, I'd suggest marking the periphs bus node
as "compatible="simple-bus","syscon";" so you could have a
reference to it, but that doesn't seem to work well in the second
case, unless you can a separate DT node just for the PHY config
registers there.

With the third case, is there any logic at all behind the
register map?

Maybe someone else has a better idea for how to describe this.
In general, we try to avoid overlapping "reg" properties, but I
even see that the "periphs" node  on gxbb has a "reg" property
(is this intentional) that overlaps with the registers in its
ranges, so adding another one won't make this worse than it
already is.

	Arnd