Re: [PATCH v5 00/18] power: sequencing: implement the subsystem and add first users

[neil.armstrong@linaro.org]

On 19/02/2024 10:22, Dmitry Baryshkov wrote:
> On Mon, 19 Feb 2024 at 10:14, Neil Armstrong <neil.armstrong@linaro.org> wrote:
>>
>> On 18/02/2024 13:53, Dmitry Baryshkov wrote:
>>> On Fri, 16 Feb 2024 at 22:33, Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>>>>
>>>> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>>>>
>>>> First, I'd like to apologize for the somewhat chaotic previous iterations
>>>> of this series and improper versioning which was rightfully pointed out
>>>> to me. I figured that the scope changed so much that it didn't make sense
>>>> to consider previous submissions part of the same series as the original
>>>> RFC but others thought otherwise so this one becomes v5 and I'll keep the
>>>> versioning going forward.
>>>>
>>>> This is the summary of the work so far:
>>>>
>>>> v1: Original RFC:
>>>>
>>>> https://lore.kernel.org/lkml/20240104130123.37115-1-brgl@bgdev.pl/T/
>>>>
>>>> v2: First real patch series (should have been PATCH v2) adding what I
>>>>       referred to back then as PCI power sequencing:
>>>>
>>>> https://lore.kernel.org/linux-arm-kernel/2024021413-grumbling-unlivable-c145@gregkh/T/
>>>>
>>>> v3: RFC for the DT representation of the PMU supplying the WLAN and BT
>>>>       modules inside the QCA6391 package (was largely separate from the
>>>>       series but probably should have been called PATCH or RFC v3):
>>>>
>>>> https://lore.kernel.org/all/CAMRc=Mc+GNoi57eTQg71DXkQKjdaoAmCpB=h2ndEpGnmdhVV-Q@mail.gmail.com/T/
>>>>
>>>> v4: Second attempt at the full series with changed scope (introduction of
>>>>       the pwrseq subsystem, should have been RFC v4)
>>>>
>>>> https://lore.kernel.org/lkml/20240201155532.49707-1-brgl@bgdev.pl/T/
>>>>
>>>> ===
>>>>
>>>> With that out of the way, I'd like to get down to explaining the two
>>>> problems I'm trying to solve.
>>>>
>>>> Problem statement #1: Dynamic bus chicken-and-egg problem.
>>>>
>>>> Certain on-board PCI devices need to be powered up before they are can be
>>>> detected but their PCI drivers won't get bound until the device is
>>>> powered-up so enabling the relevant resources in the PCI device driver
>>>> itself is impossible.
>>>>
>>>> Problem statement #2: Sharing inter-dependent resources between devices.
>>>>
>>>> Certain devices that use separate drivers (often on different busses)
>>>> share resources (regulators, clocks, etc.). Typically these resources
>>>> are reference-counted but in some cases there are additional interactions
>>>> between them to consider, for example specific power-up sequence timings.
>>>>
>>>> ===
>>>>
>>>> The reason for tackling both of these problems in a single series is the
>>>> fact the the platform I'm working on - Qualcomm RB5 - deals with both and
>>>> both need to be addressed in order to enable WLAN and Bluetooth support
>>>> upstream.
>>>>
>>>> The on-board WLAN/BT package - QCA6391 - has a Power Management Unit that
>>>> takes inputs from the host and exposes LDO outputs consumed by the BT and
>>>> WLAN modules which can be powered-up and down independently. However
>>>> a delay of 100ms must be respected between enabling the BT- and
>>>> WLAN-enable GPIOs[*].
>>>>
>>>> ===
>>>>
>>>> This series is logically split into several sections. I'll go
>>>> patch-by-patch and explain each step.
>>>>
>>>> Patch 1/18:
>>>>
>>>> This is a commit taken from the list by Jonathan Cameron that adds
>>>> a __free() helper for OF nodes. Not strictly related to the series but
>>>> until said commit ends in next, I need to carry it with this series.
>>>>
>>>> Patch 2/18:
>>>>
>>>> This enables the ath12k PCI module in arm64 defconfig as Qualcomm sm8650
>>>> and sm8550 reference platforms use it in the WCN7850 module.
>>>>
>>>> Patches 3/18-6/18:
>>>>
>>>> These contain all relevant DT bindings changes. We add new documents for
>>>> the QCA6390 PMU and ATH12K devices as well as extend the bindings for the
>>>> Qualcomm Bluetooth and ATH11K modules with regulators used by them in
>>>> QCA6390.
>>>>
>>>> Patches 7/18-9/18:
>>>>
>>>> These contain changes to device-tree sources for the three platforms we
>>>> work with in this series. As the WCN7850 module doesn't require any
>>>> specific timings introducing dependencies between the Bluetooth and WLAN
>>>> modules, while the QCA6390 does, we take two different approaches to how
>>>> me model them in DT.
>>>>
>>>> For WCN7850 we hide the existence of the PMU as modeling it is simply not
>>>> necessary. The BT and WLAN devices on the device-tree are represented as
>>>> consuming the inputs (relevant to the functionality of each) of the PMU
>>>> directly.
>>>
>>> We are describing the hardware. From the hardware point of view, there
>>> is a PMU. I think at some point we would really like to describe all
>>> Qualcomm/Atheros WiFI+BT units using this PMU approach, including the
>>> older ath10k units present on RB3 (WCN3990) and db820c (QCA6174).
>>
>> While I agree with older WiFi+BT units, I don't think it's needed for
>> WCN7850 since BT+WiFi are now designed to be fully independent and PMU is
>> transparent.
> 
> I don't see any significant difference between WCN6750/WCN6855 and
> WCN7850 from the PMU / power up point of view. Could you please point
> me to the difference?
> 

The WCN7850 datasheet clearly states there's not contraint on the WLAN_EN
and BT_EN ordering and the only requirement is to have all input regulators
up before pulling up WLAN_EN and/or BT_EN.

This makes the PMU transparent and BT and WLAN can be described as independent.

Neil