linux-kernel - Re: [PATCH 3/3] of: make default address and size cells sizes private

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Date:   Wed, 5 Sep 2018 05:37:32 +0100
From:   Mark Cave-Ayland <mark.cave-ayland@...nde.co.uk>
To:     Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>, sparclinux@...r.kernel.org
Subject: Re: [PATCH 3/3] of: make default address and size cells sizes private

On 05/09/18 02:55, Frank Rowand wrote:

> On 08/30/18 12:05, Rob Herring wrote:
>> Only some old OpenFirmware implementations rely on default sizes. Any
>> FDT and modern implementation should have explicit properties. Make the
>> OF_ROOT_NODE_*_CELLS_DEFAULT defines private so we don't get any outside
>> users.
>>
>> This also gets us one step closer to removing the asm/prom.h dependency on
>> Sparc.

Just for the record: you say "any FDT and modern implementation should
have explicit properties", however the default values of these
properties when missing are clearly defined in the IEEE-1275
specification (Annex A):

"#address-cells"
Standard property name to define the package’s address format.
...
In a package with a "decode-unit" method, a missing "#address-cells"
property signifies that the number of
address cells is two.

"#size-cells"
Standard property name to define the package’s address size format.
...
A missing "#size-cells" property signifies the default value of one.

I can't speak for FDT but it isn't completely unreasonable for a guest
parsing a DT without these properties to assume these default values.

ATB,

Mark.