linux-kernel - Re: [PATCH 1/6] dt/bindings: adjust bindings for Layerscape SCFG MSI

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Date:   Thu, 27 Oct 2016 15:18:54 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Leo Li <leoyang.li@....com>
Cc:     "M.H. Lian" <minghuan.lian@....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>,
        Marc Zyngier <marc.zyngier@....com>,
        Stuart Yoder <stuart.yoder@....com>,
        Scott Wood <scott.wood@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Mingkai Hu <mingkai.hu@....com>
Subject: Re: [PATCH 1/6] dt/bindings: adjust bindings for Layerscape SCFG MSI

On Wed, Oct 26, 2016 at 10:09:07PM +0000, Leo Li wrote:
> 
> > -----Original Message-----
> > From: Mark Rutland [mailto:mark.rutland@....com]
> > Sent: Wednesday, October 26, 2016 5:31 AM
> > To: M.H. Lian <minghuan.lian@....com>
> > Cc: linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> > devicetree@...r.kernel.org; Marc Zyngier <marc.zyngier@....com>; Stuart
> > Yoder <stuart.yoder@....com>; Leo Li <leoyang.li@....com>; Scott Wood
> > <scott.wood@....com>; Shawn Guo <shawnguo@...nel.org>; Mingkai Hu
> > <mingkai.hu@....com>
> > Subject: Re: [PATCH 1/6] dt/bindings: adjust bindings for Layerscape SCFG MSI
> > 
> > On Tue, Oct 25, 2016 at 08:35:40PM +0800, Minghuan Lian wrote:

> > > -- compatible: should be "fsl,<soc-name>-msi" to identify
> > > -	      Layerscape PCIe MSI controller block such as:
> > > -              "fsl,1s1021a-msi"
> > > -              "fsl,1s1043a-msi"
> > > +- compatible: should be "fsl,ls-scfg-msi"
> > 
> > This breaks old DTBs, and throws away information which you describe above as
> > valuable. So another NAK for that.
> 
> I agree with you that we should maintain the backward compatibility.
> But on the other hand, I just found that there is a silly typo in the
> original binding that "ls" is wrongly spelled as "1s" and they look
> too close to be noticed in previous patch reviews.  :(

Sure, that's annoying, but we're stuck with it.

> The driver and all the DTSes used the binding with the typo which
> covered up the problem.  So even if we want to keep the
> "fsl,<soc-name>-msi" binding, we probably want to fix the typo, right?
> And that breaks the backward compatibility too.

Regardless of what we do, we should *not* break compatibility. The old
strings must remain.

However, we can *add* correctly-spelt variants, and mark the existing
strings as deprecated (in both the binding and driver). The in-kernel
dts can be updated to use the correctly-spelt strings.

Thanks,
Mark.