linux-kernel - Re: [PATCH 1/2] RISC-V: Add DT documentation for SiFive L2 Cache Controller

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Date:   Wed, 1 May 2019 19:41:30 -0500
From:   Rob Herring <robh@...nel.org>
To:     Yash Shah <yash.shah@...ive.com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-kernel@...r.kernel.org, aou@...s.berkeley.edu,
        mark.rutland@....com, Sachin Ghadi <sachin.ghadi@...ive.com>
Subject: Re: [PATCH 1/2] RISC-V: Add DT documentation for SiFive L2 Cache
 Controller

On Tue, Apr 30, 2019 at 09:50:45AM +0530, Yash Shah wrote:
> On Fri, Apr 26, 2019 at 3:04 PM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Fri, Apr 26, 2019 at 11:20:17AM +0530, Yash Shah wrote:
> > > On Thu, Apr 25, 2019 at 3:43 PM Sudeep Holla <sudeep.holla@....com> wrote:
> > > >
> > > > On Thu, Apr 25, 2019 at 11:24:55AM +0530, Yash Shah wrote:
> > > > > Add device tree bindings for SiFive FU540 L2 cache controller driver
> > > > >
> > > > > Signed-off-by: Yash Shah <yash.shah@...ive.com>
> > > > > ---
> > > > >  .../devicetree/bindings/riscv/sifive-l2-cache.txt  | 53 ++++++++++++++++++++++
> > > > >  1 file changed, 53 insertions(+)
> > > > >  create mode 100644 Documentation/devicetree/bindings/riscv/sifive-l2-cache.txt
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/riscv/sifive-l2-cache.txt b/Documentation/devicetree/bindings/riscv/sifive-l2-cache.txt
> > > > > new file mode 100644
> > > > > index 0000000..15132e2
> > > > > --- /dev/null
> > > > > +++ b/Documentation/devicetree/bindings/riscv/sifive-l2-cache.txt
> > > > > @@ -0,0 +1,53 @@
> > > > > +SiFive L2 Cache Controller
> > > > > +--------------------------
> > > > > +The SiFive Level 2 Cache Controller is used to provide access to fast copies
> > > > > +of memory for masters in a Core Complex. The Level 2 Cache Controller also
> > > > > +acts as directory-based coherency manager.
> > > > > +
> > > > > +Required Properties:
> > > > > +--------------------
> > > > > +- compatible: Should be "sifive,fu540-c000-ccache"
> > > > > +
> > > > > +- cache-block-size: Specifies the block size in bytes of the cache
> > > > > +
> > > > > +- cache-level: Should be set to 2 for a level 2 cache
> > > > > +
> > > > > +- cache-sets: Specifies the number of associativity sets of the cache
> > > > > +
> > > > > +- cache-size: Specifies the size in bytes of the cache
> > > > > +
> > > > > +- cache-unified: Specifies the cache is a unified cache
> > > > > +
> > > > > +- interrupt-parent: Must be core interrupt controller
> > > > > +
> > > > > +- interrupts: Must contain 3 entries (DirError, DataError and DataFail signals)
> > > > > +
> > > > > +- reg: Physical base address and size of L2 cache controller registers map
> > > > > +
> > > > > +- reg-names: Should be "control"
> > > > > +
> > > >
> > > > It would be good if you mark the properties that are present in DT
> > > > specification and those that are added for sifive,fu540-c000-ccache
> > >
> > > I believe there isn't any property which is added explicitly for
> > > sifive,fu540-c000-ccache.
> > >
> >
> > reg and interrupts are generally optional for normal cache and may be
> > required for cache controller like this. DT specification[1] covers
> > only caches and not cache controllers.
> 
> Are you suggesting something like this:
> 
> Required Properties:
> --------------------
> Standard Properties:

I don't think we need this separation.

> - compatible: Should be "sifive,<chip>-ccache"
>   Supported compatible strings are:
>   "sifive,fu540-c000-ccache" and "sifive,fu740-c000-ccache"
> 
> - cache-block-size: Specifies the block size in bytes of the cache
> 
> - cache-level: Should be set to 2 for a level 2 cache
> 
> - cache-sets: Specifies the number of associativity sets of the cache
> 
> - cache-size: Specifies the size in bytes of the cache

What are the possible valid values for these? That's what's important. 
What the properties mean are already defined in the spec.

> 
> - cache-unified: Specifies the cache is a unified cache
> 
> Non-Standard Properties:

I wouldn't call these non-standard.

> - interrupt-parent: Must be core interrupt controller

This is implied.

> 
> - interrupts: Must contain 3 entries for FU540 (DirError, DataError and
>   DataFail signals) or 4 entries for other chips (DirError, DirFail, DataError,
>   DataFail signals)
> 
> - reg: Physical base address and size of L2 cache controller registers map
> 
> - reg-names: Should be "control"

-names is not really needed when there is only 1 entry.

> 
> - Yash
> >
> > --
> > Regards,
> > Sudeep
> >
> > [1] https://github.com/devicetree-org/devicetree-specification/releases/download/v0.2/devicetree-specification-v0.2.pdf