Re: [PATCH] devfreq: exynos-bus: workaround dev_pm_opp_set_rate() errors on Exynos5422/5800 SoCs

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hi

On 14.11.2019 08:38, Chanwoo Choi wrote:
> On 11/14/19 3:07 PM, Chanwoo Choi wrote:
>> On 11/14/19 12:12 AM, Kamil Konieczny wrote:
>>> On 14.10.2019 08:46, Chanwoo Choi wrote:
>>>> On 19. 10. 11. 오후 8:33, Marek Szyprowski wrote:
>>>>> On 10.10.2019 04:50, Chanwoo Choi wrote:
>>>>>> On 2019년 10월 08일 22:49, k.konieczny@partner.samsung.com wrote:
>>>>>>> Commit 4294a779bd8d ("PM / devfreq: exynos-bus: Convert to use
>>>>>>> dev_pm_opp_set_rate()") introduced errors:
>>>>>>> exynos-bus: new bus device registered: soc:bus_wcore ( 84000 KHz ~ 400000 KHz)
>>>>>>> exynos-bus: new bus device registered: soc:bus_noc ( 67000 KHz ~ 100000 KHz)
>>>>>>> exynos-bus: new bus device registered: soc:bus_fsys_apb (100000 KHz ~ 200000 KHz)
>>>>>>> ...
>>>>>>> exynos-bus soc:bus_wcore: dev_pm_opp_set_rate: failed to find current OPP for freq 532000000 (-34)
>>>>>>> exynos-bus soc:bus_noc: dev_pm_opp_set_rate: failed to find current OPP for freq 111000000 (-34)
>>>>>>> exynos-bus soc:bus_fsys_apb: dev_pm_opp_set_rate: failed to find current OPP for freq 222000000 (-34)
>>>>>>>
>>>>>>> They are caused by incorrect PLL assigned to clock source, which results
>>>>>>> in clock rate outside of OPP range. Add workaround for this in
>>>>>>> exynos_bus_parse_of() by adjusting clock rate to those present in OPP.
>>>>>> If the clock caused this issue, you can set the initial clock on DeviceTree
>>>>>> with assigned-clock-* properties. Because the probe time of clock driver
>>>>>> is early than the any device drivers.
>>>>>>
>>>>>> It is not proper to fix the clock issue on other device driver.
>>>>>> I think you can fix it by using the supported clock properties.
>>>>> This issue is about something completely different. The OPPs defined in
>>>>> DT cannot be applied, because it is not possible to derive the needed
>>>>> clock rate from the bootloader-configured clock topology (mainly due to
>>>>> lack of common divisor values for some of the parent clocks). Some time
>>>>> ago Lukasz tried initially to redefine this clock topology using
>>>>> assigned-clock-rates/parents properties (see
>>>>> https://protect2.fireeye.com/url?k=4b80c0304459bc8e.4b814b7f-f87f1e1aee1a85c0&u=https://lkml.org/lkml/2019/7/15/276), but it has limitations and some
>>>>> such changes has to be done in bootloader. Until this is resolved,
>>>>> devfreq simply cannot set some of the defined OPPs.
>>>> As you mentioned, the wrong setting in bootloader cause the this issue.
>>>> So, this patch change the rate on exynos-bus.c in order to fix
>>>> the issue with workaround style.
>>>>
>>>> But, also, it can be fixed by initializing the clock rate on DT
>>>> although it is not fundamental solution as you mentioned.
>>>>
>>>> If above two method are workaround way, I think that set the clock
>>>> rate in DT is proper. The role of 'assigned-clock-*' properties
>>>> is for this case in order to set the initial frequency on probe time.
>>> I can add 'assigned-clock-*' to DT, but the issue is caused in opp points,
>>> so the warning from exynos-bus will still be there.
>>>
>>> Before this fix, devfreq will issue warning and then change clock to max
>>> frequency within opp range. This fix mask warning, and as Marek and
>>> Lukasz Luba wrotes, the proper fix will be to make changes in u-boot
>>> (and connect proper PLLs to IPs).
>> PLL could be changed by clock device driver in the linux kernel.
>> If you don't add the supported frequency into PLL frequency table
>> of clock device driver, will fail to change the wanted frequency
>> on the linux kernel. It means that it is not fixed by only touching
>> the bootloader.
>>
>> As you commented, the wrong opp points which are specified on dt
>> cause this issue. Usually, have to initialize the clock rate on dt
>> by using 'assigned-clocks-*' property and then use the clock
>> with the preferable clock rate. I think that we have to fix
>> the fundamental problem.
>>
>> Without bootloader problem, you can fix it by initializing
>> the clock on dt with 'assigned-clocks-*' property.
>>
>> As I knew that it is correct way and I always tried to do this method
>> for resolving the similar clock issue.
>>
>> Lastly, I think that my opinion is more simple and correct.
>> It could give the more correct information to linux kernel user
>> which refer to the device tree file.
>>
>> 1. Your suggestion
>> 	a. Add opp-table with unsupported frequency on dt
>> 	b. Try to change the clock rate on exynos-bus.c by using unsupported frequency from opp-table
>> 	c. If failed, retry to change the clock rate on exynos-bus.c
>>
>> 2. My opinion
>> 	a. Initialize the PLL or any clock by using assigned-clock-* property on dt
>> 	   and add opp-table with supported frequency on dt
>> 	b. Try to change the clock rate on exynos-bus.c by using supported frequency from opp-table
>>
> Just I tried to add 'assigned-clock-rates' property to initialize
> the clock rate of some bus node as following on odroid-xu3 board:
>
> diff --git a/arch/arm/boot/dts/exynos5422-odroid-core.dtsi b/arch/arm/boot/dts/exynos5422-odroid-core.dtsi
> index 829147e320e0..9a237af5436a 100644
> --- a/arch/arm/boot/dts/exynos5422-odroid-core.dtsi
> +++ b/arch/arm/boot/dts/exynos5422-odroid-core.dtsi
> @@ -42,6 +42,8 @@
>   };
>   
>   &bus_wcore {
> +       assigned-clocks = <&clock CLK_DOUT_ACLK400_WCORE>;
> +       assigned-clock-rates = <400000000>;
>          devfreq-events = <&nocp_mem0_0>, <&nocp_mem0_1>,
>                          <&nocp_mem1_0>, <&nocp_mem1_1>;
>          vdd-supply = <&buck3_reg>;
> @@ -50,11 +52,15 @@
>   };
>   
>   &bus_noc {
> +       assigned-clocks = <&clock CLK_DOUT_ACLK100_NOC>;
> +       assigned-clock-rates = <100000000>;
>          devfreq = <&bus_wcore>;
>          status = "okay";
>   };
>   
>   &bus_fsys_apb {
> +       assigned-clocks = <&clock CLK_DOUT_PCLK200_FSYS>;
> +       assigned-clock-rates = <200000000>;
>          devfreq = <&bus_wcore>;
>          status = "okay";
>   };
> @@ -120,6 +126,8 @@
>   };
>   
>   &bus_mscl {
> +       assigned-clocks = <&clock CLK_DOUT_ACLK400_MSCL>;
> +       assigned-clock-rates = <400000000>;
>          devfreq = <&bus_wcore>;
>          status = "okay";
>   };


Well, this is a poor workaround. There is indeed no warning, but the 
clock rates are far from the specified in the device tree. For WCORE 
assigned-clock-rates = <400000000> on Odroid XU3/XU4 kernel will set 
dout_aclk400_wcore clock to 266MHz, because it is not possible to derive 
400MHz from 532MHz MPLL...

I plan to measure the impact of different rates on the performance of 
the various components and overall power consumption. Only then IMHO it 
makes sense to decide if we really should adjust OPPs to the current 
PLLs configuration (-> basically define following OPPs for WCORE: 
532MHz, 266MHz, 133MHZ and 77MHz) or change PLL configuration and 
re-parent WCORE to 1200MHz to properly drive: 400MHz, 300MHz, 200MHz and 
100MHz.

Other devfreq buses should IMHO use the values similar to the selected 
for WCORE.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland