linux-kernel - RE: [PATCH v6 2/6] dt-bindings: Add the rzn1-clocks.h file

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Date:   Wed, 30 May 2018 13:49:09 +0000
From:   Phil Edworthy <phil.edworthy@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     M P <buserror@...il.com>,
        Michel Pollet <michel.pollet@...renesas.com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Simon Horman <horms@...ge.net.au>,
        Michel Pollet <buserror+upstream@...il.com>,
        "Magnus Damm" <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Michael Turquette <mturquette@...libre.com>,
        "Stephen Boyd" <sboyd@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: RE: [PATCH v6 2/6] dt-bindings: Add the rzn1-clocks.h file

Hi Geert,

On 30 May 2018 14:37 Geert Uytterhoeven wrote:
> On Wed, May 30, 2018 at 3:30 PM, Phil Edworthy wrote:
> > On 25 May 2018 10:13 Geert Uytterhoeven wrote:
> >  [snip]
> >
> >> Now, given the clock definitions for RZ/N1[DSL] are the same
> >> (although some don't exist on some variants), you could keep on using
> >> RZN1_CLK_FOO for the names of the defines, and store them in a
> common
> >> file, included by the soc-specific file. But please make clear the
> >> common file cannot be included directly, so the filename does not
> >> become part of the DT ABI, and you are shielded from future marketing
> >> silliness (e.g. next quarter's RZ/N1X being totally different).
> > How does an include filename become part of the DT ABI?
> > I thought the dtb is the ABI, not the dts. Am I wrong?
> 
> You're right. In se the DT ABI applies to the DTB, not to the DTS.
> 
> The definitions inside the include file are part of the DT bindings, and thus
> cannot be changed.  Your DTS files get these definitions by including the
> header file, so the header filename is also part of the bindings, and thus can't
> be changed that easily.
That seems a bit onerous... 
It makes sense that bindings that affect the dtb can only be added to, so that
an old dtb still works. However, I would have thought it's the value of the
constant that is the ABI, not the symbol name used to specify it.

Thanks for you feedback!
Phil