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

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Date:   Fri, 10 Mar 2017 12:03:12 +0000
From:   Artur Jedrysek <jartur@...ence.com>
To:     Marek Vasut <marek.vasut@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>
CC:     "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>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: RE: [v2, 4/4] dt-bindings: mtd: Add Octal SPI support to Cadence
 QSPI.


> 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?

> 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.

> > +  Use "cdns,qspi-nor" for Quad SPI controller.
> > +  Use "cdns,ospi-nor" for Octal SPI controller.
> >  - reg : Contains two entries, each of which is a tuple consisting of a
> >  	physical address and length. The first entry is the address and
> >  	length of the controller register set. The second entry is the
> >
> 
> 
> --
> Best regards,
> Marek Vasut