linux-kernel - Re: [RFC-next 0/1] Odroid C2: Enable DVFS for cpu

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Message-ID: <CAFBinCCgKcwXSLxS_CRvz9JZvQo8PcUGm=egBbabVZSrkSc30Q@mail.gmail.com>
Date:   Thu, 12 Dec 2019 21:09:55 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Kevin Hilman <khilman@...libre.com>,
        Anand Moon <linux.amoon@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-amlogic@...ts.infradead.org,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC-next 0/1] Odroid C2: Enable DVFS for cpu

Hi Neil,

On Wed, Dec 11, 2019 at 9:49 AM Neil Armstrong <narmstrong@...libre.com> wrote:
>
> On 10/12/2019 22:47, Kevin Hilman wrote:
> > Martin Blumenstingl <martin.blumenstingl@...glemail.com> writes:
> >
> >> On Tue, Dec 10, 2019 at 7:13 PM Kevin Hilman <khilman@...libre.com> wrote:
> >>>
> >>> Anand Moon <linux.amoon@...il.com> writes:
> >>>
> >>>> Hi Neil / Kevin,
> >>>>
> >>>> On Tue, 10 Dec 2019 at 14:13, Neil Armstrong <narmstrong@...libre.com> wrote:
> >>>>>
> >>>>> On 09/12/2019 23:12, Kevin Hilman wrote:
> >>>>>> Anand Moon <linux.amoon@...il.com> writes:
> >>>>>>
> >>>>>>> Some how this patch got lost, so resend this again.
> >>>>>>>
> >>>>>>> [0] https://patchwork.kernel.org/patch/11136545/
> >>>>>>>
> >>>>>>> This patch enable DVFS on GXBB Odroid C2.
> >>>>>>>
> >>>>>>> DVFS has been tested by running the arm64 cpuburn
> >>>>>>> [1] https://github.com/ssvb/cpuburn-arm/blob/master/cpuburn-a53.S
> >>>>>>> PM-QA testing
> >>>>>>> [2] https://git.linaro.org/power/pm-qa.git [cpufreq testcase]
> >>>>>>>
> >>>>>>> Tested on latest U-Boot 2019.07-1 (Aug 01 2019 - 23:58:01 +0000) Arch Linux ARM
> >>>>>>
> >>>>>> Have you tested with the Harkernel u-boot?
> >>>>>>
> >>>>>> Last I remember, enabling CPUfreq will cause system hangs with the
> >>>>>> Hardkernel u-boot because of improperly enabled frequencies, so I'm not
> >>>>>> terribly inclined to merge this patch.
> >>>>
> >>>> HK u-boot have many issue with loading the kernel, with load address
> >>>> *it's really hard to build the kernel for HK u-boot*,
> >>>> to get the configuration correctly.
> >>>>
> >>>> Well I have tested with mainline u-boot with latest ATF .
> >>>> I would prefer mainline u-boot for all the Amlogic SBC, since
> >>>> they sync with latest driver changes.
> >>>
> >>> Yes, we would all prefer mainline u-boot, but the mainline kernel needs
> >>> to support the vendor u-boot that is shipping with the boards.  So
> >>> until Hardkernel (and other vendors) switch to mainline u-boot we do not
> >>> want to have upstream kernel defaults that will not boot with the vendor
> >>> u-boot.
> >>>
> >>> We can always support these features, but they just cannot be enabled
> >>> by default.
> >> (I don't have an Odroid-C2 but I'm curious)
> >> should Anand submit a patch to mainline u-boot instead?
> >
> > It would be in addition to $SUBJECT patch, not instead, I think.
> >
> >> the &scpi_clocks node could be enabled at runtime by mainline u-boot
> >
> > That would work, but I don't know about u-boot maintainers opinions on
> > this kind of thing, so let's see what Neil thinks.
>
> U-Boot doesn't anything to do with SCPI, SCPI discusses directly with the SCP
> processor, and the CPU clock is set to 1,56GHz by the BL2 boot stage before
> U-boot starts.
>
> The only viable solution I see now is to find if we could add a DT OPP table
> only for Odroid-C2 dts to bypass the SCPI OPP table.
my understanding is that mainline u-boot (with whatever SCP firmware
it uses) provides the *correct* OPP table
in this case it would be "safe" to have SCPI enabled with mainline u-boot
@Anand: please correct me if I misunderstood you

my idea to "enable SCPI with mainline u-boot" is to have u-boot update
the "status" property of the scpi_clocks node.
u-boot does something similar with the mac-address property of the
Ethernet controller for example.
as result of this users of mainline u-boot would have working CPU
DVFS, while users of the old vendor u-boot would run at fixed 1.54GHz.


Martin