linux-kernel - Re: [v2, 4/4] dt-bindings: mtd: Add Octal SPI support to Cadence QSPI.

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Date:   Wed, 15 Mar 2017 15:23:24 -0500
From:   Rob Herring <robh@...nel.org>
To:     Marek Vasut <marek.vasut@...il.com>
Cc:     Artur Jedrysek <jartur@...ence.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [v2, 4/4] dt-bindings: mtd: Add Octal SPI support to Cadence
 QSPI.

On Fri, Mar 10, 2017 at 01:52:31PM +0100, Marek Vasut wrote:
> On 03/10/2017 01:03 PM, Artur Jedrysek wrote:
> > 
> >> From: Marek Vasut [mailto:marek.vasut@...il.com]
> >> Sent: 10 March 2017 04:39
> >> On 03/08/2017 09:05 AM, Artur Jedrysek wrote:
> >>> This patch updates Cadence QSPI Device Tree documentation to include
> >>> information about new compatible used to indicate, whether or not
> >>> Octal SPI transfers are supported by the device.
> >>>
> >>> Signed-off-by: Artur Jedrysek <jartur@...ence.com>
> >>> ---
> >>> Changelog:
> >>> v2: Use new compatible, instead of boolean property, to indicate
> >>> Octal SPI support.
> >>> ---
> >>>  Documentation/devicetree/bindings/mtd/cadence-quadspi.txt | 4 +++-
> >>>  1 file changed, 3 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/mtd/cadence-quadspi.txt
> >> b/Documentation/devicetree/bindings/mtd/cadence-quadspi.txt
> >>> index f248056..41d1e98 100644
> >>> --- a/Documentation/devicetree/bindings/mtd/cadence-quadspi.txt
> >>> +++ b/Documentation/devicetree/bindings/mtd/cadence-quadspi.txt
> >>> @@ -1,7 +1,9 @@
> >>>  * Cadence Quad SPI controller
> >>>
> >>>  Required properties:
> >>> -- compatible : Should be "cdns,qspi-nor".
> >>> +- compatible : Should be "cdns,{qspi|ospi}-nor".
> >>
> >> Please explicitly list all compatibles , ie.
> >> Should be "cdns,qspi-nor" or "cdns,ospi-nor".
> >>
> > 
> > Two possible options are also explicitly listed right below. I did that
> > in the way it was done in other driver for Cadence IP:
> > /Documentation/devicetree/bindings/net/macb.txt
> > Should I remove all of that and replace it with both options, separated
> > by an "or" word?
> 
> Wait for Rob to confirm.

As Marek suggested, but with one valid combination per line. I don't 
think checkpatch.pl will work with it as is.

> 
> >> But I think the ospi is backward compatible with qspi, right ? So the
> >> binding for ospi should list both, ie.
> >> compatible = "cdns,ospi-nor", "cdns,qspi-nor";
> >>
> > 
> > Yes, the ospi is backwards compatible with qspi. However, the sole point
> > of introducing new compatible was to differentiate between them (which
> > was previously done using a boolean flag, but that was criticized).
> > Listing both bindings for ospi would only help for kernels not
> > containing driver update being subject of this patch series, as both
> > ospi and qspi are handled by the same driver - just with a slight
> > difference. I apologize if I got something wrong here.
> 
> You got it right, I was just curious about the compatibility.

You are assuming every OS/user everywhere is updated. It doesn't hurt to 
have the backwards compatibility.

Rob