linux-kernel - Re: [Letux-kernel] [RFC PATCH 0/3] Enable 1GHz support on omap36xx

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Message-ID: <CAHCN7xLyeSFCMn=qhmYa0ZsqsQheHDz8zyBz38giECK9wixbuw@mail.gmail.com>
Date:   Mon, 9 Sep 2019 11:38:47 -0500
From:   Adam Ford <aford173@...il.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     "H. Nikolaus Schaller" <hns@...delico.com>,
        André Roth <neolynx@...il.com>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andreas Kemnade <andreas@...nade.info>,
        Nishanth Menon <nm@...com>
Subject: Re: [Letux-kernel] [RFC PATCH 0/3] Enable 1GHz support on omap36xx

On Mon, Sep 9, 2019 at 11:32 AM Tony Lindgren <tony@...mide.com> wrote:
>
> Hi,
>
> * H. Nikolaus Schaller <hns@...delico.com> [190909 14:57]:
> > Another question that came up by private mail from André was if we
> > should better disable the turbo OPPs of omap34xx and 36xx by default
> > (status = "disabled";) because there are concerns about overheating
> > the chips and we have no thermal regulation like for omap4 & 5.

I thought there was a thermal sensor?

cpu_thermal: cpu_thermal {
        polling-delay-passive = <250>; /* milliseconds */
        polling-delay = <1000>; /* milliseconds */
        coefficients = <0 20000>;

                        /* sensor       ID */
        thermal-sensors = <&bandgap     0>;
};

Can this driver somehow notify the cpufreq that we've hit some limit?
I know it's not as accurate as one would like, but even for non-1GHz
versions, having it downclock would be a good thing when running at
extreme temps.

adam
> >
> > But this would mean that every board DTS would have to set it explicitly
> > to "enabled".
>
> Yes I started thinking about that too. I think there is a requirement
> to do the scaling via the voltage processor for the higher modes.
> And there needs to be some way to automatically change to a lower
> OPP in some cases.
>
> For normal OPPs, using the twl regulator directly should be OK.
>
> For the higher modes, maybe we could pass the callback functions
> from arch/arm/mach-omap2/voltage.c for the twl regulator so the
> voltage processor hardware can handle them directly. Or add a
> separate regulator driver operating the voltages like Nishanth
> posted patches for earlier.
>
> Regards,
>
> Tony