linux-kernel - Re: [PATCH 15/15] arm: dts: imx: Add missing OPP properties for CPUs

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Date:   Tue, 3 Jul 2018 15:12:16 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Lucas Stach <l.stach@...gutronix.de>, arm@...nel.org,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-kernel@...r.kernel.org, chris.redpath@....com,
        ionela.voinescu@....com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 15/15] arm: dts: imx: Add missing OPP properties for CPUs

On Mon, May 28, 2018 at 04:37:39PM +0530, Viresh Kumar wrote:
> Hi Lucas,
> 
> On 25-05-18, 13:46, Lucas Stach wrote:
> > This is a lot of duplicate information for what is effectively a shared
> >  cluster wide thing. This does absolutely not _feel_ right.
> 
> I cannot agree more :)
> 
> > What problem are you solving here? Why do we need all this duplicate
> > information? Why can't we fix it by falling back to looking at cpu0 if
> > needed?
> 
> Let me try explaining one of the problem scenarios to you as your
> platform is a single cluster one. Make cpufreq driver as module, don't
> insert it, hotplug out CPU0 and now insert the cpufreq driver. The
> cpufreq core will try adding the cpufreq policy for CPU1 but wouldn't
> find the required information in the DT node of CPU1 and so will fail
> or behave incorrectly.
> 
> We can't look at CPU0 as we don't know they are related at all.
> Nothing tells that to us. The right solution to fix the duplication is
> to move to OPP-v2 bindings, which allow us to create a single OPP
> table node and refer to it from all the CPU nodes. Because in case of
> imx platforms getting updated here, we use the old and some platforms
> specific frequency tables, we have to duplicate it everywhere.
> 
> But looking from DT otherwise, all the device should anyway have all
> the information required right in their node. That can be simplified
> with things like phandle to opp-v2 node, but still everything needs to
> be there. We shouldn't really rely on other CPU nodes to make it work.
> That would be an incomplete definition of the hardware IMHO.

Lucas,

Are you fine with the patch now considering the respond from Viresh?

Shawn