linux-kernel - Re: [PATCH v2 2/4] Documentation: Add documentation for APM X-Gene SoC PMU DTS binding

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Date:	Mon, 2 May 2016 14:46:05 -0700
From:	Tai Tri Nguyen <ttnguyen@....com>
To:	Rob Herring <robh@...nel.org>
Cc:	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>, catalin.marinas@....com,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	patches <patches@....com>
Subject: Re: [PATCH v2 2/4] Documentation: Add documentation for APM X-Gene
 SoC PMU DTS binding

Hi Rob,

On Mon, May 2, 2016 at 1:56 PM, Rob Herring <robh@...nel.org> wrote:
> On Wed, Apr 20, 2016 at 12:31:22PM +0100, Will Deacon wrote:
>> On Mon, Apr 18, 2016 at 01:04:53PM -0700, Tai Tri Nguyen wrote:
>> > >> +Required properties for MCB subnode:
>> > >> +- compatible         : Shall be "apm,xgene-pmu-mcb".
>> > >> +- reg                        : First resource shall be the MCB PMU resource.
>> > >> +- index                      : Instance number of the MCB PMU.
>> > >> +
>> > >> +Required properties for MC subnode:
>> > >> +- compatible         : Shall be "apm,xgene-pmu-mc".
>> > >> +- reg                        : First resource shall be the MC PMU resource.
>> > >> +- index                      : Instance number of the MC PMU.
>> > >
>> > > Don't use indexes. You probably need phandles to the nodes these are
>> > > related to.
>> > >
>> > > How many variations of child nodes do you expect to have? 2, 10, 50? You
>> > > might want to just collapse all this down to a single node and put this
>> > > information in the driver if it is fixed for each SoC and there's only a
>> > > handful.
>> > >
>> >
>> > For each kind of PMU, for example memory controller PMU, I expect to
>> > have the number of instances up to 8.
>> > They are actually all independent PMU nodes and have their own CSR memory bases.
>> > The indexes are used for exposing the devices to perf user only. It
>> > doesn't have an impact on the programming model.
>> > Mark also had the same concern.
>>
>> Regardless, I'll need an ack from Rob or Mark before I can merge this.
>
> I still have a concern with this. Needing an index to expose to the user
> is generally not a valid reason. That's OS specific and therefore
> doesn't belong in DT.
>
> Rob

I can use device name here. However, the perf event names will be
different between DT and ACPI which I want to avoid.
And the names don't look good at all.
Also, specifically for MC and MCB PMUs, the indexes are compared
against the active MC/MCB mask to find out whether they are populated
or not.
Without using the index property, I will also need a mapping function
of physical device addresses and their physical ids.

Thanks,
-- 
Tai