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

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Date:	Mon, 6 Jun 2016 18:29:45 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Tai Tri Nguyen <ttnguyen@....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

On Tue, May 31, 2016 at 06:25:56PM -0700, Tai Tri Nguyen wrote:
> Hi Mark,

[...]

> 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.

Ah, I see.

Can you elaborate on how the indicator bits are laid out? From the
example binding, I see multiple nodes with the same index property, so
I'm a little confused.

I guess that there's a CSR per class of node (e.g. all MCBs in one CSR
register)? Or do several nodes share the same bit?

Is there a single CSR register? Are there several? Is that bit index
used in other registers?

> 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?

Assuming it's always a single bit, a *-bit-index property may be fine,
and probably preferable.

I'm a little confused, so I'd like to understand how it's used.

Thanks,
Mark.