linux-kernel - Re: [RESEND PATCH 2/4] dt-bindings: add "reduced-width" property for Armada XP SDRAM controller

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Date:   Fri, 11 Aug 2017 11:34:27 +0200
From:   Jan Lübbe <jlu@...gutronix.de>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
        Rob Herring <robh@...nel.org>
Cc:     "gregory.clement@...e-electrons.com" 
        <gregory.clement@...e-electrons.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [RESEND PATCH 2/4] dt-bindings: add "reduced-width" property
 for Armada XP SDRAM controller

On Thu, 2017-08-10 at 21:17 +0000, Chris Packham wrote:
> On 11/08/17 08:38, Rob Herring wrote:
> > On Mon, Aug 07, 2017 at 01:46:39PM +1200, Chris Packham wrote:
[...]  
> > > +Optional properties:
> > > + - marvell,reduced-width: some SoCs that use this SDRAM controller have
> > > +   a reduced pin count. On such systems "full" width is 32-bits and
> > > +   "half" width is 16-bits. Set this property to indicate that the SoC
> > > +   used is such a system.
> > 
> > Maybe you should just state what the width is.
> 
> Specifying a number like 64/32/16 is done in for some other properties I 
> dismissed that because what this is about how we interpret a 
> pin-strapping option. I guess "max-width = <64>;" and "max-width = 
> <32>"; would achieve the same.
> 
> > Or your compatible string should just be specific enough to know the
> > width.
> 
> I decided against a new compatible sting that because the IP block 
> really is the Armada-XP one and the existing compatible string is used 
> in other places (using multiple compatible strings would solve that).
> 
> I'm not too fussed which of the 3 options are used. Is there any 
> particular preference?

I'd prefer a specific compatible string, as it would avoid adding even
more properties if further difference turn up.

Rob, I seem to remember that some drivers match the top-level
compatible against a list of SoC variants to detect SoC-dependent
features in a generic IP block. Is that something you'd prefer instead?

Regards,
Jan