linux-kernel - Re: [TEGRA194_CPUFREQ Patch 1/3] firmware: tegra: adding function to get BPMP data

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Message-ID: <20191204095138.rrul5vxnkprfwmku@vireshk-i7>
Date:   Wed, 4 Dec 2019 15:21:38 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mikko Perttunen <cyndis@...si.fi>,
        Sumit Gupta <sumitg@...dia.com>, rjw@...ysocki.net,
        catalin.marinas@....com, will@...nel.org, jonathanh@...dia.com,
        talho@...dia.com, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, bbasu@...dia.com,
        mperttunen@...dia.com, devicetree@...r.kernel.org
Subject: Re: [TEGRA194_CPUFREQ Patch 1/3] firmware: tegra: adding function to
 get BPMP data

On 04-12-19, 10:33, Thierry Reding wrote:
> Yeah, the code that registers this device is in drivers/base/cpu.c in
> register_cpu(). It even retrieves the device tree node for the CPU from
> device tree and stores it in cpu->dev.of_node, so we should be able to
> just pass &cpu->dev to tegra_bpmp_get() in order to retrieve a reference
> to the BPMP.
> 
> That said, I'm wondering if perhaps we could just add a compatible
> string to the /cpus node for cases like this where we don't have an
> actual device representing the CPU complex. There are a number of CPU
> frequency drivers that register dummy devices just so that they have
> something to bind a driver to.
> 
> If we allow the /cpus node to represent the CPU complex (if no other
> "device" does that yet), we can add a compatible string and have the
> cpufreq driver match on that.
> 
> Of course this would be slightly difficult to retrofit into existing
> drivers because they'd need to remain backwards compatible with existing
> device trees. But it would allow future drivers to do this a little more
> elegantly. For some SoCs this may not matter, but especially once you
> start depending on additional resources this would come in handy.
> 
> Adding Rob and the device tree mailing list for feedback on this idea.

Took some time to find this thread, but something around this was
suggested by Rafael earlier.

https://lore.kernel.org/lkml/8139001.Q4eV8YG1Il@vostro.rjw.lan/

-- 
viresh