Re: [PATCH v1 08/16] arm64: dts: mt8195: Add power domains controller

From: Krzysztof Kozlowski
Date: Tue Jul 12 2022 - 08:58:54 EST

On 12/07/2022 14:54, AngeloGioacchino Del Regno wrote:
> Il 12/07/22 14:47, Krzysztof Kozlowski ha scritto:
>> On 12/07/2022 12:33, AngeloGioacchino Del Regno wrote:
>>> Il 12/07/22 11:03, Krzysztof Kozlowski ha scritto:
>>>> On 12/07/2022 10:53, AngeloGioacchino Del Regno wrote:
>>>>> Il 12/07/22 10:37, Krzysztof Kozlowski ha scritto:
>>>>>> On 12/07/2022 10:17, AngeloGioacchino Del Regno wrote:
>>>>>>> Il 06/07/22 17:18, Krzysztof Kozlowski ha scritto:
>>>>>>>> On 06/07/2022 14:00, Tinghan Shen wrote:
>>>>>>>>> Hi Krzysztof,
>>>>>>>>> After discussing your message with our power team,
>>>>>>>>> we realized that we need your help to ensure we fully understand you.
>>>>>>>>> On Mon, 2022-07-04 at 14:38 +0200, Krzysztof Kozlowski wrote:
>>>>>>>>>> On 04/07/2022 12:00, Tinghan Shen wrote:
>>>>>>>>>>> Add power domains controller node for mt8195.
>>>>>>>>>>> Signed-off-by: Weiyi Lu <>
>>>>>>>>>>> Signed-off-by: Tinghan Shen <tinghan.shen@xxxxxxxxxxxx>
>>>>>>>>>>> ---
>>>>>>>>>>> arch/arm64/boot/dts/mediatek/mt8195.dtsi | 327 +++++++++++++++++++++++
>>>>>>>>>>> 1 file changed, 327 insertions(+)
>>>>>>>>>>> diff --git a/arch/arm64/boot/dts/mediatek/mt8195.dtsi b/arch/arm64/boot/dts/mediatek/mt8195.dtsi
>>>>>>>>>>> index 8d59a7da3271..d52e140d9271 100644
>>>>>>>>>>> --- a/arch/arm64/boot/dts/mediatek/mt8195.dtsi
>>>>>>>>>>> +++ b/arch/arm64/boot/dts/mediatek/mt8195.dtsi
>>>>>>>>>>> @@ -10,6 +10,7 @@
>>>>>>>>>>> #include <dt-bindings/interrupt-controller/irq.h>
>>>>>>>>>>> #include <dt-bindings/phy/phy.h>
>>>>>>>>>>> #include <dt-bindings/pinctrl/mt8195-pinfunc.h>
>>>>>>>>>>> +#include <dt-bindings/power/mt8195-power.h>
>>>>>>>>>>> / {
>>>>>>>>>>> compatible = "mediatek,mt8195";
>>>>>>>>>>> @@ -338,6 +339,332 @@
>>>>>>>>>>> #interrupt-cells = <2>;
>>>>>>>>>>> };
>>>>>>>>>>> + scpsys: syscon@10006000 {
>>>>>>>>>>> + compatible = "syscon", "simple-mfd";
>>>>>>>>>> These compatibles cannot be alone.
>>>>>>>>> the scpsys sub node has the compatible of the power domain driver.
>>>>>>>>> do you suggest that the compatible in the sub node should move to here?
>>>>>>>> Not necessarily, depends. You have here device node representing system
>>>>>>>> registers. They need they own compatibles, just like everywhere in the
>>>>>>>> kernel (except the broken cases...).
>>>>>>>> Whether this should be compatible of power-domain driver, it depends
>>>>>>>> what this device node is. I don't know, I don't have your datasheets or
>>>>>>>> your architecture diagrams...
>>>>>>>>>>> + reg = <0 0x10006000 0 0x1000>;
>>>>>>>>>>> + #power-domain-cells = <1>;
>>>>>>>>>> If it is simple MFD, then probably it is not a power domain provider.
>>>>>>>>>> Decide.
>>>>>>>>> this MFD device is the power controller on mt8195.
>>>>>>>> Then it is not a simple MFD but a power controller. Do not use
>>>>>>>> "simple-mfd" compatible.
>>>>>>>>> Some features need
>>>>>>>>> to do some operations on registers in this node. We think that implement
>>>>>>>>> the operation of these registers as the MFD device can provide flexibility
>>>>>>>>> for future use. We want to clarify if you're saying that an MFD device
>>>>>>>>> cannot be a power domain provider.
>>>>>>>> MFD device is Linuxism, so it has nothing to do here. I am talking only
>>>>>>>> about simple-mfd. simple-mfd is a simple device only instantiating
>>>>>>>> children and not providing anything to anyone. Neither to children. This
>>>>>>>> the most important part. The children do not depend on anything from
>>>>>>>> simple-mfd device. For example simple-mfd device can be shut down
>>>>>>>> (gated) and children should still operate. Being a power domain
>>>>>>>> controller, contradicts this usually.
>>>>>>> If my interpretation of this issue is right, I have pushed a solution for it.
>>>>>>> Krzysztof, Matthias, can you please check [1] and give feedback, so that
>>>>>>> Tinghan can rewrite this commit ASAP?
>>>>>>> Reason is - I need the MT8195 devicetree to be complete to push the remaining
>>>>>>> pieces for Tomato Chromebooks, of course.
>>>>>>> [1]:
>>>>>> I have two or three similar discussions, so maybe I lost the context,
>>>>>> but I don't understand how your fix is matching real hardware.
>>>>>> In the patchset here, Tinghan claimed that power domain controller is a
>>>>>> child of 10006000. 10006000 is also a power domain controller. This was
>>>>>> explicitly described by the DTS code.
>>>>>> Now you abandon this hierarchy in favor of syscon. If the hierarchy was
>>>>>> correct, your patchset does not match the hardware, so it's a no-go.
>>>>>> Describe the hardware.
>>>>>> However maybe this patch did not make any sense and there is no
>>>>>> relationship parent-child... so what do you guys send here? Bunch of
>>>>>> hacks and work-arounds?
>>>>> For how I get it, hardware side, the SPM (System Power Manager) resides inside
>>>>> of the SCPSYS block (consequently, in that iospace).
>>>>> As Matthias pointed out earlier, SCPSYS provides more functionality, but the
>>>>> only one that's currently implemented upstream is the System Power Manager,
>>>>> responsible for managing the MTCMOS (power domains).
>>>>> In any case, now I'm a little confused on how to proceed, can you please give
>>>>> some suggestion?
>>>> You should make SCPSYS (0x10006000, AFAIU) a proper driver with its own
>>>> compatible (followed by syscon if needed), even if now it is almost
>>>> empty stub. The driver should populate OF children and then you can
>>>> embed SPM inside and reference to parent's regmap. No need for
>>>> simple-mfd. Later the SCPSYS can grow, if you ever need it.
>>> I see an issue with such approach: the SCPSYS doesn't have a mailbox, doesn't
>>> need power management from the Linux side, doesn't have any register to check
>>> HW revision, it's always online (hence it doesn't need Linux to boot it), it
>>> doesn't need any root clock, nor regulator, nor mmu context, and there's no
>>> retrievable "boot log" of any sort.
>> No problems, there are other drivers who do not need any resources,
>> except address space.
>>> Hence, a driver with its own compatible would be an empty stub forever: it's
>>> not going to get any "scpsys root handling" at all, because there's none to do.
>> But it is a power domain provider, so you need to embed it in some
>> dirver, don't you?
>>> Digging through some downstream kernels, the only other functionality that I
>>> can find in the SCPSYS is a MODULE_RESET (which is used to reset the SCP System)
>>> and a INFRA_IRQ_SET, used to set "wake locks" on the AP and CONNSYS (modem).
>> So why was power domain provider added to SCPSYS? Guys, I don't know
>> your architecture, so I deduct it based on pieces of DTS code I see.
>>> Both of these may only be used in the SCP mailbox driver (which is *not* SCPSYS)
>>> to perform an ipi_send operation (but currently we simply en/disable the clock
>>> and that's enough), or to perform a reset and firmware reload of the SCP (but
>>> currently we're simply powering off and back on: this may change in the future).
>>> So, at the end of the day, we would end up having a copy of simple-pm-bus and
>>> nothing else, which doesn't look like being optimal at all.
>> No, because you need that power domain driver, don't you? If you don't
>> need power domain provider/driver, why the heck this is there:
>> + scpsys: syscon@10006000 {
>> + compatible = "syscon", "simple-mfd";
>> + reg = <0 0x10006000 0 0x1000>;
>> + #power-domain-cells = <1>;
>> ^^^^^^^^^^^^^^^^^
>> Entire discussion started from this.
> Is this all a huge misunderstanding? It probably is, at least partially.
> That node shouldn't have any #power-domain-cells, the only PD is the SPM node
> (mediatek,mt8195-power-controller), not the scpsys parent! Ugh...

My comment was quite clear I think:

> + #power-domain-cells = <1>;
If it is simple MFD, then probably it is not a power domain provider.

and you keep telling me that it is a power domain provider and MFD and
something more.

Anyway neither syscon nor simple-mfd can be without specific compatible.

Best regards,