Re: [PATCH 0/9] PCI: introduce the concept of power sequencing of PCIe devices

[Dmitry Baryshkov]

On Wed, 17 Jan 2024 at 20:16, Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxx> wrote:
>
> On Wed, 17 Jan 2024 at 18:08, Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> >
> > From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> >
> > The responses to the RFC were rather positive so here's a proper series.
> >
> > During last year's Linux Plumbers we had several discussions centered
> > around the need to power-on PCI devices before they can be detected on
> > the bus.
> >
> > The consensus during the conference was that we need to introduce a
> > class of "PCI slot drivers" that would handle the power-sequencing.
> >
> > After some additional brain-storming with Manivannan and the realization
> > that DT maintainers won't like adding any "fake" nodes not representing
> > actual devices, we decided to reuse existing PCI infrastructure.
> >
> > The general idea is to instantiate platform devices for child nodes of
> > the PCIe port DT node. For those nodes for which a power-sequencing
> > driver exists, we bind it and let it probe. The driver then triggers a
> > rescan of the PCI bus with the aim of detecting the now powered-on
> > device. The device will consume the same DT node as the platform,
> > power-sequencing device. We use device links to make the latter become
> > the parent of the former.
> >
> > The main advantage of this approach is not modifying the existing DT in
> > any way and especially not adding any "fake" platform devices.
>
> I'd still like to see how this can be extended to handle BT power up,
> having a single entity driving both of the BT and WiFI.
>
> The device tree changes behave in exactly the opposite way: they
> define regulators for the WiFi device, while the WiFi is not being
> powered by these regulators. Both WiFi and BT are powered by the PMU,
> which in turn consumes all specified regulators.

Some additional justification, why I think that this should be
modelled as a single instance instead of two different items.

This is from msm-5.10 kernel:


===== CUT HERE =====
/**
 * cnss_select_pinctrl_enable - select WLAN_GPIO for Active pinctrl status
 * @plat_priv: Platform private data structure pointer
 *
 * For QCA6490, PMU requires minimum 100ms delay between BT_EN_GPIO off and
 * WLAN_EN_GPIO on. This is done to avoid power up issues.
 *
 * Return: Status of pinctrl select operation. 0 - Success.
 */
static int cnss_select_pinctrl_enable(struct cnss_plat_data *plat_priv)
===== CUT HERE =====


Also see the bt_configure_gpios() function in the same kernel.


>
> >
> > Changes since RFC:
> > - move the pwrseq functionality out of the port driver and into PCI core
> > - add support for WCN7850 to the first pwrseq driver (and update bindings)
> > - describe the WLAN modules in sm8550-qrd and sm8650-qrd
> > - rework Kconfig options, drop the defconfig changes from the series as
> >   they are no longer needed
> > - drop the dt-binding changes for PCI vendor codes
> > - extend the DT bindings for ath11k_pci with strict property checking
> > - various minor tweaks and fixes
> >
> > Bartosz Golaszewski (7):
> >   arm64: dts: qcom: qrb5165-rb5: describe the WLAN module of QCA6390
> >   PCI: create platform devices for child OF nodes of the port node
> >   PCI: hold the rescan mutex when scanning for the first time
> >   PCI/pwrseq: add pwrseq core code
> >   dt-bindings: wireless: ath11k: describe QCA6390
> >   dt-bindings: wireless: ath11k: describe WCN7850
> >   PCI/pwrseq: add a pwrseq driver for QCA6390
> >
> > Neil Armstrong (2):
> >   arm64: dts: qcom: sm8550-qrd: add Wifi nodes
> >   arm64: dts: qcom: sm8650-qrd: add Wifi nodes
> >
> >  .../net/wireless/qcom,ath11k-pci.yaml         |  89 ++++++
> >  arch/arm64/boot/dts/qcom/qrb5165-rb5.dts      |  29 ++
> >  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 +
> >  drivers/pci/Kconfig                           |   1 +
> >  drivers/pci/Makefile                          |   1 +
> >  drivers/pci/bus.c                             |   9 +-
> >  drivers/pci/probe.c                           |   2 +
> >  drivers/pci/pwrseq/Kconfig                    |  16 ++
> >  drivers/pci/pwrseq/Makefile                   |   4 +
> >  drivers/pci/pwrseq/pci-pwrseq-qca6390.c       | 267 ++++++++++++++++++
> >  drivers/pci/pwrseq/pwrseq.c                   |  82 ++++++
> >  drivers/pci/remove.c                          |   3 +-
> >  include/linux/pci-pwrseq.h                    |  24 ++
> >  17 files changed, 621 insertions(+), 2 deletions(-)
> >  create mode 100644 drivers/pci/pwrseq/Kconfig
> >  create mode 100644 drivers/pci/pwrseq/Makefile
> >  create mode 100644 drivers/pci/pwrseq/pci-pwrseq-qca6390.c
> >  create mode 100644 drivers/pci/pwrseq/pwrseq.c
> >  create mode 100644 include/linux/pci-pwrseq.h
> >
> > --
> > 2.40.1
> >
> >
>
>
> --
> With best wishes
> Dmitry



-- 
With best wishes
Dmitry