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

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On Fri, 16 Feb 2024 at 22:33, Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> 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:
> v2: First real patch series (should have been PATCH v2) adding what I
>     referred to back then as PCI power sequencing:
> 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):
> v4: Second attempt at the full series with changed scope (introduction of
>     the pwrseq subsystem, should have been RFC v4)
> ===
> 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).

> For QCA6390 on RB5 we add the PMU node as a platform device. It consumes
> regulators and GPIOs from the host and exposed regulators consumer in turn
> by the BT and WLAN modules. This represents the internal structure of the
> package.
> Patches 10/18-14/18:
> These contain the bulk of the PCI changes for this series. We introduce
> a simple framework for powering up PCI devices before detecting them on
> the bus and the first user of this library in the form of the WCN7850 PCI
> power control driver.
> The general approach is as follows: PCI devices that need special
> treatment before they can be powered up, scanned and bound to their PCI
> drivers must be described on the device-tree as child nodes of the PCI
> port node. These devices will be instantiated on the platform bus. They
> will in fact be generic platform devices with the compatible of the form
> used for PCI devices already upstream ("pci<vendor ID>,<device ID">). We
> add a new directory under drivers/pci/pwrctl/ that contains PCI pwrctl
> drivers. These drivers are platform drivers that will now be matched
> against the devices instantiated from port children just like any other
> platform pairs.
> Both the power control platform device *AND* the associated PCI device
> reuse the same OF node and have access to the same properties. The goal
> of the platform driver is to request and bring up any required resources
> and let the pwrctl framework know that it's now OK to rescan the bus and
> detect the devices. When the device is bound, we are notified about it
> by the PCI bus notifier event and can establish a device link between the
> power control device and the PCI device so that any future extension for
> power-management will already be able to work with the correct hierachy.
> The reusing of the OF node is the reason for the small changes to the PCI
> OF core: as the bootloader can possibly leave the relevant regulators on
> before booting linux, the PCI device can be detected before its platform
> abstraction is probed. In this case, we find that device first and mark
> its OF node as reused. The pwrctl framework handles the opposite case
> (when the PCI device is detected only after the platform driver
> successfully enabled it).
> Patches 15/18-16/18:
> These add a relatively simple power sequencing subsystem and the first
> driver using it: the pwrseq module for the QCA6390 PMU.
> For the record: Bjorn suggested a different solution: a regulator driver
> that would - based on which regulators are enabled by a consumer - enable
> relevant resources (drive the enable GPIOs) while respecting the
> HW-specific delays. This would however require significant and yet
> unprecised changed to the regulator subsystem as well as be an abuse of
> the regulator provider API akin to using the reset framework for power
> sequencing as proposed before.
> Instead I'm proposing to add a subsystem that allows different devices to
> use a shared power sequence split into consumer-specific as well as
> common "units".
> A power sequence provider driver registers a set of units with pwrseq
> core. Each unit can be enabled and disabled and contains an optional list
> of other units which must be enabled before it itself can be. A unit
> represents a discreet chunk of the power sequence.
> It also registers a list of targets: a target is an abstraction wrapping
> a unit which allows consumers to tell pwrseq which unit they want to
> reach. Real-life example is the driver we're adding here: there's a set
> of common regulators, two PCIe-specific ones and two enable GPIOs: one
> for Bluetooth and one for WLAN.
> The Bluetooth driver requests a descriptor to the power sequencer and
> names the target it wants to reach:
>     pwrseq = devm_pwrseq_get(dev, "bluetooth");

Is this target tied to the device or not? If not, this might become a
limitation, if somebody installs two WiFi/BT modules to a single

> The pwrseq core then knows that when the driver calls:
>     pwrseq_power_on(pwrseq);
> It must enable the "bluetooth-enable" unit but it depends on the
> "regulators-common" unit so this one is enabled first. The provider
> driver is also in charge of assuring an appropriate delay between
> enabling the BT and WLAN enable GPIOs. The WLAN-specific resources are
> handled by the "wlan-enable" unit and so are not enabled until the WLAN
> driver requests the "wlan" target to be powered on.
> Another thing worth discussing is the way we associate the consumer with
> the relevant power sequencer. DT maintainers have expressed a discontent
> with the existing mmc pwrseq bindings and have NAKed an earlier
> initiative to introduce global pwrseq bindings to the kernel[1].
> In this approach, we model the existing regulators and GPIOs in DT but
> the pwrseq subsystem requires each provider to provide a .match()
> callback. Whenever a consumer requests a power sequencer handle, we
> iterate over the list of pwrseq drivers and call .match() for each. It's
> up to the driver to verify in a platform-specific way whether it deals
> with its consumer and let the core pwrseq code know.

This looks really nice, it will allow us to migrate the BT driver to
always use pwrseq instead of regulators without touching the DT.

> The advantage of this over reusing the regulator or reset subsystem is
> that it's more generalized and can handle resources of all kinds as well
> as deal with any kind of power-on sequences: for instance, Qualcomm has
> a PCI switch they want a driver for but this switch requires enabling
> some resources first (PCI pwrctl) and then configuring the device over
> I2C (which can be handled by the pwrseq provider).
> Patch 17/18:
> This patch makes the Qualcomm Bluetooth driver get and use the power
> sequencer for QCA6390.
> Patch 18/18:
> While tiny, this patch is possibly the highlight of the entire series.
> It uses the two abstraction layers we introduced before to create an
> elegant power sequencing PCI power control driver and supports the ath11k
> module on QCA6390.
> With this series we can now enable BT and WLAN on several new Qualcomm
> boards upstream.
> I tested the series on RB5 while Neil tested it on sm8650-qrd and
> sm8550-qrd.
> Best Regards,
> Bartosz Golaszewski
> It's hard to list the changes between versions here as the scope changed
> significantly between each iteration and some versions were not even full
> series but rather RFCs for parts of the solution. For this reason, I'll
> only start listing changes starting from v6.
> [*] This is what the docs say. In practice it seems that this delay can be
> ignored. However the subsequent model - QCA6490 - *does* require users to
> respect it, so the problem remains valid.
> [1]
> Bartosz Golaszewski (15):
>   arm64: defconfig: enable ath12k as a module
>   dt-bindings: regulator: describe the PMU module of the QCA6390 package
>   dt-bindings: net: bluetooth: qualcomm: describe regulators for QCA6390
>   dt-bindings: new: wireless: qcom,ath11k: describe the ath11k on
>     QCA6390
>   dt-bindings: new: wireless: describe the ath12k PCI module
>   arm64: dts: qcom: qrb5165-rb5: model the PMU of the QCA6391
>   PCI: hold the rescan mutex when scanning for the first time
>   PCI/pwrctl: reuse the OF node for power controlled devices
>   PCI/pwrctl: create platform devices for child OF nodes of the port
>     node
>   PCI/pwrctl: add PCI power control core code
>   PCI/pwrctl: add a power control driver for WCN7850
>   power: sequencing: implement the pwrseq core
>   power: pwrseq: add a driver for the QCA6390 PMU module
>   Bluetooth: qca: use the power sequencer for QCA6390
>   PCI/pwrctl: add a PCI power control driver for power sequenced devices
> Jonathan Cameron (1):
>   of: Add cleanup.h based auto release via __free(device_node) markings.
> Neil Armstrong (2):
>   arm64: dts: qcom: sm8550-qrd: add the Wifi node
>   arm64: dts: qcom: sm8650-qrd: add the Wifi node
>  .../net/bluetooth/qualcomm-bluetooth.yaml     |   17 +
>  .../net/wireless/qcom,ath11k-pci.yaml         |   28 +
>  .../net/wireless/qcom,ath12k-pci.yaml         |  103 ++
>  .../bindings/regulator/qcom,qca6390-pmu.yaml  |  166 +++
>  MAINTAINERS                                   |    8 +
>  arch/arm64/boot/dts/qcom/qrb5165-rb5.dts      |  123 +-
>  arch/arm64/boot/dts/qcom/sm8250.dtsi          |   10 +
>  arch/arm64/boot/dts/qcom/sm8550-qrd.dts       |   37 +
>  arch/arm64/boot/dts/qcom/sm8550.dtsi          |   10 +
>  arch/arm64/boot/dts/qcom/sm8650-qrd.dts       |   29 +
>  arch/arm64/boot/dts/qcom/sm8650.dtsi          |   10 +
>  arch/arm64/configs/defconfig                  |    1 +
>  drivers/bluetooth/hci_qca.c                   |   31 +
>  drivers/pci/Kconfig                           |    1 +
>  drivers/pci/Makefile                          |    1 +
>  drivers/pci/bus.c                             |    9 +-
>  drivers/pci/of.c                              |   14 +-
>  drivers/pci/probe.c                           |    2 +
>  drivers/pci/pwrctl/Kconfig                    |   25 +
>  drivers/pci/pwrctl/Makefile                   |    7 +
>  drivers/pci/pwrctl/core.c                     |  136 +++
>  drivers/pci/pwrctl/pci-pwrctl-pwrseq.c        |   84 ++
>  drivers/pci/pwrctl/pci-pwrctl-wcn7850.c       |  202 ++++
>  drivers/pci/remove.c                          |    2 +
>  drivers/power/Kconfig                         |    1 +
>  drivers/power/Makefile                        |    1 +
>  drivers/power/sequencing/Kconfig              |   28 +
>  drivers/power/sequencing/Makefile             |    6 +
>  drivers/power/sequencing/core.c               | 1065 +++++++++++++++++
>  drivers/power/sequencing/pwrseq-qca6390.c     |  353 ++++++
>  include/linux/of.h                            |    2 +
>  include/linux/pci-pwrctl.h                    |   51 +
>  include/linux/pwrseq/consumer.h               |   56 +
>  include/linux/pwrseq/provider.h               |   75 ++
>  34 files changed, 2678 insertions(+), 16 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/net/wireless/qcom,ath12k-pci.yaml
>  create mode 100644 Documentation/devicetree/bindings/regulator/qcom,qca6390-pmu.yaml
>  create mode 100644 drivers/pci/pwrctl/Kconfig
>  create mode 100644 drivers/pci/pwrctl/Makefile
>  create mode 100644 drivers/pci/pwrctl/core.c
>  create mode 100644 drivers/pci/pwrctl/pci-pwrctl-pwrseq.c
>  create mode 100644 drivers/pci/pwrctl/pci-pwrctl-wcn7850.c
>  create mode 100644 drivers/power/sequencing/Kconfig
>  create mode 100644 drivers/power/sequencing/Makefile
>  create mode 100644 drivers/power/sequencing/core.c
>  create mode 100644 drivers/power/sequencing/pwrseq-qca6390.c
>  create mode 100644 include/linux/pci-pwrctl.h
>  create mode 100644 include/linux/pwrseq/consumer.h
>  create mode 100644 include/linux/pwrseq/provider.h
> --
> 2.40.1

With best wishes

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