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

[Neil Armstrong <narmstrong@baylibre.com>]

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.

The arm,scpi-clocks driver registers a clk for this CPU clock, using SCPI to set
the rate, right now this is ok.

But, arm,scpi-clocks also registers a "scpi-cpufreq" device, which calls
scpi_ops->add_opps_to_device() which gets the SCPI OPPs and adds them to the CPU.

A way to handle this would be to check if DT has OPPs in drivers/cpufreq/scpi-cpufreq.c
_before/instead_ calling scpi_ops->add_opps_to_device() to use the DT OPPs instead
of the firmware OPPs, like in drivers/cpufreq/cpufreq-dt.c.

calling:

	ret = dev_pm_opp_of_get_sharing_cpus()
	if (ret) {
		scpi_ops->add_opps_to_device()
		scpi_get_sharing_cpus()
	}

would maybe work.

Neil

> 
> Kevin
> 
>