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

[Neil Armstrong]

On 16/02/2024 21:31, Bartosz Golaszewski 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:
>
> https://lore.kernel.org/lkml/20240104130123.37115-1-brgl@xxxxxxxx/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@xxxxxxxxxxxxxx/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@xxxxxxxx/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.
>
> 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");
>
> 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.
>
> 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] https://lore.kernel.org/netdev/20210829131305.534417-1-dmitry.baryshkov@xxxxxxxxxx/
>
> 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

Tested-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx> # on SM8650-QRD
Tested-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx> # on SM8550-QRD

Thanks,
Neil