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

[Anand Moon <linux.amoon@gmail.com>]

Hi Neil

On Fri, 13 Dec 2019 at 18:54, Neil Armstrong <narmstrong@baylibre.com> wrote:
>
> On 13/12/2019 12:28, Anand Moon wrote:
> > Hi Martin
> >
> > On Fri, 13 Dec 2019 at 01:40, Martin Blumenstingl
> > <martin.blumenstingl@googlemail.com> wrote:
> >>
> >> Hi Neil,
> >>
> >> On Wed, Dec 11, 2019 at 9:49 AM Neil Armstrong <narmstrong@baylibre.com> wrote:
> >>>
> >>> On 10/12/2019 22:47, Kevin Hilman wrote:
> >>>> Martin Blumenstingl <martin.blumenstingl@googlemail.com> writes:
> >>>>
> >>>>> On Tue, Dec 10, 2019 at 7:13 PM Kevin Hilman <khilman@baylibre.com> wrote:
> >>>>>>
> >>>>>> Anand Moon <linux.amoon@gmail.com> writes:
> >>>>>>
> >>>>>>> Hi Neil / Kevin,
> >>>>>>>
> >>>>>>> On Tue, 10 Dec 2019 at 14:13, Neil Armstrong <narmstrong@baylibre.com> wrote:
> >>>>>>>>
> >>>>>>>> On 09/12/2019 23:12, Kevin Hilman wrote:
> >>>>>>>>> Anand Moon <linux.amoon@gmail.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
> >
> > Right now I am not sure how this OPP table is populated.
> > But I saw the same freq table used in 3.16.x kernel after enable the clk.
> >
> >> in this case it would be "safe" to have SCPI enabled with mainline u-boot
> >> @Anand: please correct me if I misunderstood you
> >>
> >
> > As per my understanding DVFS OPP frequency table for SCPI firmware set
> > for 1.536 GHz
> > somewhere in BL2 as pointed by Neil.
> >
> > Arm Trusted firmware added new secure SCPI communication with
> > Cortex-M3 co processor.
> > [0] https://github.com/ARM-software/arm-trusted-firmware/blob/master/docs/plat/meson-gxbb.rst
> > [1] https://github.com/ARM-software/arm-trusted-firmware/blob/master/plat/amlogic/common/aml_scpi.c
> >
> > ATF generated the *bl1.bin* which is replace the Amlogic's bl1.bin
> > while preparing
> > the new u-boot *u-boot.gxbb* image.
> >
> >> 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
> >
> > Right now as per my understanding 1.536 GHz max is bit under clocked.
> >
> > Some time ago on Odroid Forum tried to over clock the cpu to 2GHz.
>
> This is the point, the Odroid-C2 is *not* stable at 2GHz,
> a large amount of board doesn't support 2GHz, this is why Amlogic
> dropped the freq > 1.536 GHz for the GXBB family.
>
> But HardKernel still delivers the SCPI table with > 1.536 GHz which breaks
> on most of the boards, but doesn't on 3.14 since they have a hack disabling
> higher freqs with a cmdline set in boot.ini.
>
> > [3] https://forum.odroid.com/viewtopic.php?f=139&t=18738
> > So more investigation need to done in this line.
> >
> > I also tried the same with HardKernel Image, with modifying the boot.ini
> > I could increase the max DVFS cpu frequency to 1.90 GHz,
> > This is just proof of concept.
> >
> > odroid:~# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
> > 100000 250000 500000 1000000 1296000 1536000 1656000 1680000 1752000 1896000
> >
> > I have some minimal stress testing attached are the results for HK
> > 3.16.x kernel.
> >
> > For now we should not enable this clock.
> > Until we can possible to check for higher clock frequency to work stable
> > on all Amlogic S905X SBC.
> >
> > I like the Neil's approach to use it's own dts OPP table for SCPI protocol.
>
> The various tests gave very little perf enhancement by going > 1,536 GHz, seriously
> it's not worth the pain.
>
> Neil
>

Ok Thanks for your expert knowledge.
I agree with you completely on this to set max freq to 1,536 GHz for
all S905 SoC.

-Anand