On Thu, 18 Jan 2024 15:29:01 +0100, Rob Herring [off-list ref] said:

On Wed, Jan 17, 2024 at 10:08 AM Bartosz Golaszewski [off-list ref] wrote:

[snip]

quoted

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.

Suspend/resume has been brought up already, but I disagree we can
worry about that later unless there is and always will be no power
sequencing during suspend/resume for all devices ever. Given the
supplies aren't standard, it wouldn't surprise me if standard PCI
power management isn't either. The primary issue I see with this
design is we will end up with 2 drivers doing the same power
sequencing: the platform driver for initial power on and the device's
PCI driver for suspend/resume.

Rob

I admit that I don't have any HW where I could test it but I my thinking was
that with the following relationships between the devices:

                  ┌─────────────────────┐
                  │                     │
                  │   PCI Port device   │
                  │                     │
                  └───┬───────────┬─────┘
                      │           │
                      │           │
                      │           │
┌─────────────────────▼─────┐     │
│                           │     │
│   QCA6390 pwrseq device   │     │
│                           │     │
└─────────────────────┬─────┘     │
                      │           │
                      │           │
                      │           │
                ┌─────▼───────────▼───┐
                │                     │
                │  ath11k_pci device  │
                │                     │
                └─────────────────────┘

the PM subsystem would handle the dependencies automatically and correctly
setup the sequence for suspend and resume. Also: the PCI ath11k driver does
not deal with the kind of resources that the power sequencing platform driver
handles: regulators, GPIOs and clocks.

I agree, it would be useful to have a working case of handling suspend/resume
with this code though.

Bartosz

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