linux-kernel - Re: [PATCH] dt-bindings: sifive: describe sifive-blocks versioning

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Date:   Wed, 5 Dec 2018 18:30:45 -0800 (PST)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Atish Patra <atish.patra@....com>
cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        "paul@...an.com" <paul@...an.com>, Megan Wachs <megan@...ive.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Wesley Terpstra <wesley@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH] dt-bindings: sifive: describe sifive-blocks versioning

Hi Atish,

On Wed, 21 Nov 2018, Atish Patra wrote:

> On 11/21/18 5:07 PM, Paul Walmsley wrote:
> > 
> > For IP blocks that are generated from the public, open-source
> > sifive-blocks repository, describe the version numbering policy
> > that its maintainers intend to use, upon request from Rob
> > Herring <robh@...nel.org>.
> > 
> > Cc: Rob Herring <robh+dt@...nel.org>
> > Cc: Palmer Dabbelt <palmer@...ive.com>
> > Cc: Megan Wachs <megan@...ive.com>
> > Cc: Wesley Terpstra <wesley@...ive.com>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: devicetree@...r.kernel.org
> > Cc: linux-riscv@...ts.infradead.org
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Paul Walmsley <paul.walmsley@...ive.com>
> > Signed-off-by: Paul Walmsley <paul@...an.com>
> > ---
> > 
> > Hi Rob, please let me know if this document works with your
> > requirements, or if some changes are needed.  - Paul
> > 
> >   .../sifive/sifive-blocks-ip-versioning.txt    | 38 +++++++++++++++++++
> >   1 file changed, 38 insertions(+)
> >   create mode 100644
> > Documentation/devicetree/bindings/sifive/sifive-blocks-ip-versioning.txt
> > 
> > diff --git
> > a/Documentation/devicetree/bindings/sifive/sifive-blocks-ip-versioning.txt
> > b/Documentation/devicetree/bindings/sifive/sifive-blocks-ip-versioning.txt
> > new file mode 100644
> > index 000000000000..b899e5c6e00c
> > --- /dev/null
> > +++
> > b/Documentation/devicetree/bindings/sifive/sifive-blocks-ip-versioning.txt
> 
> It should be be under
> Documentation/devicetree/bindings/riscv/sifive/sifive-blocks-ip-versioning.txt
> ?

These IP blocks could be used with any CPU architecture - ARM, x86, MIPS, 
etc. - so it probably makes sense just to keep them under sifive/, rather 
than associating them with a specific CPU architecture.

> > @@ -0,0 +1,38 @@
> > +DT compatible string versioning for SiFive open-source IP blocks
> > +
> > +This document describes the version specification for DT "compatible"
> > +strings for open-source SiFive IP blocks.  HDL for these IP blocks
> > +can be found in this public repository:
> > +
> > +https://github.com/sifive/sifive-blocks
> > +
> > +IP block-specific DT compatible strings are contained within the HDL,
> > +in the form "sifive,<ip-block-name><integer version number>".
> > +
> > +An example is "sifive,uart0" from:
> > +
> > +https://github.com/sifive/sifive-blocks/blob/master/src/main/scala/devices/uart/UART.scala#L43
> > +
> > +Until these IP blocks (or IP integration) support version
> > +autodiscovery, the maintainers of these IP blocks intend to increment
> 
> /s/autodiscovery/auto discovery

I've changed it to "auto-discovery" per your request.  Let me know if it's 
not OK for you

> > +the suffixed number in the compatible string whenever the software
> > +interface to these IP blocks changes, or when the functionality of the
> > +underlying IP blocks changes in a way that software should be aware of.
> > +
> > +Driver developers can use compatible string "match" values such as
> > +"sifive,uart0" to indicate that their driver is compatible with the
> > +register interface and functionality associated with the relevant
> > +upstream sifive-blocks commits.  It is expected that most drivers will
> > +match on these IP block-specific compatible strings.
> > +
> > +DT data authors, when writing data for a particular SoC, should
> > +continue to specify an SoC-specific compatible string value, such as
> > +"sifive,fu540-c000-uart".  This way, if SoC-specific
> > +integration-specific bug fixes or workarounds are needed, the kernel
> > +or other system software can match on this string to apply them.  The
> > +IP block-specific compatible string (such as "sifive,uart0") should
> > +then be specified as a subsequent value.
> > +
> > +An example of this style:
> > +
> > +    compatible = "sifive,fu540-c000-uart", "sifive,uart0";
> > 
> 
> Just for the sake of completion, should this document also specify what should
> be the style of any possible closed IP as well?


Let's handle those separately, as Palmer discussed.

Thanks for the review,

- Paul