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

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Date:	Tue, 10 May 2016 16:43:30 -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/Mark,

Do you have any more comments, please?

Thanks,
Tai

On Mon, May 2, 2016 at 2:46 PM, Tai Tri Nguyen <ttnguyen@....com> wrote:
> 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



-- 
Tai