Re: [PATCH v2 2/2] dt-bindings: introduce Command DB for QCOM SoCs

[Lina Iyer]

On Wed, Feb 14 2018 at 19:34 +0000, Bjorn Andersson wrote:
> On Thu 08 Feb 11:51 PST 2018, Lina Iyer wrote:
>
> > From: Mahesh Sivasubramanian <msivasub@xxxxxxxxxxxxxx>
> >
> > Command DB provides information on shared resources like clocks,
> > regulators etc., probed at boot by the remote subsytem and made
> > available in shared memory.
> >
> > Cc: devicetree@xxxxxxxxxxxxxxx
> > Signed-off-by: Mahesh Sivasubramanian <msivasub@xxxxxxxxxxxxxx>
> > Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
> > ---
> >  .../devicetree/bindings/arm/msm/cmd-db.txt         | 38 ++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/arm/msm/cmd-db.txt
> >
> > diff --git a/Documentation/devicetree/bindings/arm/msm/cmd-db.txt b/Documentation/devicetree/bindings/arm/msm/cmd-db.txt
> > new file mode 100644
> > index 000000000000..e21666e40ebf
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/arm/msm/cmd-db.txt
> > @@ -0,0 +1,38 @@
> > +Command DB
> > +---------
> > +
> > +Command DB is a database that provides a mapping between resource key and the
> > +resource address for a system resource managed by a remote processor. The data
> > +is stored in a shared memory region and is loaded by the remote processor.
> > +
> > +Some of the Qualcomm Technologies Inc SoC's have hardware accelerators for
> > +controlling shared resources. Depending on the board configuration the shared
> > +resource properties may change. These properties are dynamically probed by the
> > +remote processor and made available in the shared memory.
> > +
> > +The devicetree representation of the command DB driver should be:
> > +
> > +PROPERTIES:
> > +- compatible:
> > +	Usage: required
> > +	Value type: <string>
> > +	Definition: Should be "qcom,cmd-db"
> > +
> > +- memory-region:
> > +	Usage: required
> > +	Value type: <phandle>
> > +	Definition: The phandle to the reserved memory region.
> > +
> > +Example:
> > +
> > +	reserved-memory {
> > +		[...]
> > +		cmd_db_mem: qcom,cmd-db@c3f000c {
> > +			reg = <0x0 0xc3f000c 0x0 0x8>;
>
> I was hoping that we can describe the actual memory here, as I got the
> impression that it will also be a chunk of memory carved out from System
> RAM.
Yes, it can be described. But, the location should always be read from
the address above. Generally, the CMD DB memory would not change, but it
is not always guaranteed.

> If not it would seem unlikely that there's a 8 byte carveout in the
> middle of DDR, what else is here?
>
> > +		};
> > +	};
> > +
> > +	qcom,cmd-db@c3f000c {
> > +		compatible = "qcom,cmd-db";
>
> Add "qcom,cmd-db" to "reserved_mem_matches" in drivers/of/platform.c,
> use of_reserved_mem_lookup(pdev->dev.of_node) to get the reserved_mem
> and you can just put the compatible directly on the reserved-memory
> node.
>
> That way you don't need this separate node that doesn't really represent
> anything.
Oh okay. I can take care of that.

Thanks,
Lina
> > +		memory-region = <&cmd_db_mem>;
> > +	};