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

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Message-ID: <CACgAJHxMCa2Hp_A8YnHmmVrHGd3yLhFs2k33MN6OHRUmZ7Y_Wg@mail.gmail.com>
Date:	Tue, 31 May 2016 18:25:56 -0700
From:	Tai Tri Nguyen <ttnguyen@....com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Rob Herring <robh@...nel.org>, Will Deacon <will.deacon@....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 Mark,

On Tue, May 31, 2016 at 10:17 AM, Tai Tri Nguyen <ttnguyen@....com> wrote:
> Hi Mark,
>
> On Tue, May 31, 2016 at 9:56 AM, Mark Rutland <mark.rutland@....com> wrote:
>> On Mon, May 02, 2016 at 02:46:05PM -0700, Tai Tri Nguyen 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.
>>
>> What's wrong with using ${device}.{physical_address} as the PMU name?
>> That would be unique and consistent regardless of the firmware, no
>> mapping nor index property necessary.
>>
>> That's sufficient for any user already familiar with the topology, a
>> familiarity you seem to be assuming regardless by not explicitly
>> describing the topology in the DT.
>>
>> Thanks,
>> Mark.
>
> Okay. I'll do fix it for the next patches.
>
> Thanks,
> --
> Tai

I'm facing a problem after removing the index for MCU and MC sub-nodes.
The MCUs and MCs aren't always enabled depending on how DRAM DIMMs are
installed on the system.
I still need a way to associate the MCU with its indicator bit in the
enable mask retrieved from CSR.
For MC and MCB nodes only, can I introduce an "enable-mask" field?
For example:
"
pmucmcb@...10000 {
        compatible = "apm,xgene-pmu-mcb";
        reg = <0x0 0x7e710000 0x0 0x1000>;
        enable-mask = <0x00000001>;
};

pmucmcb@...30000 {
        compatible = "apm,xgene-pmu-mcb";
        reg = <0x0 0x7e730000 0x0 0x1000>;
        enable-mask = <0x00000002>;
};
"
Or can you please give a suggestion how I can fix it?

Thanks,
-- 
Tai