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

[Bartosz Golaszewski]

On Thu, 18 Jan 2024 15:29:01 +0100, Rob Herring <robh+dt@xxxxxxxxxx> said:
> On Wed, Jan 17, 2024 at 10:08 AM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
>

[snip]

>
>> 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