Re: [RFC] PCI: pwrctrl and link-up dependencies

[Manivannan Sadhasivam]

On Tue, Apr 08, 2025 at 02:26:24PM -0700, Brian Norris wrote:
> + adding pcie-brcmstb.c folks
> 
> On Tue, Apr 08, 2025 at 12:59:39PM -0700, Brian Norris wrote:
> > TL;DR: PCIe link-up may depend on pwrctrl; however, link-startup is
> > often run before pwrctrl gets involved. I'm exploring options to resolve
> > this.
> 
> Apologies if a quick self-reply is considered nosiy or rude, but I
> nearly forgot that I previously was looking at "pwrctrl"-like
> functionality and noticed that drivers/pci/controller/pcie-brcmstb.c has
> had a portion of the same "pwrctrl" functionality for some time (commit
> 93e41f3fca3d ("PCI: brcmstb: Add control of subdevice voltage
> regulators")).
> 

Yes, the goal of the pwrctrl driver is to get rid of this clutter from the
controller drivers.

> Notably, it performs its power sequencing before starting its link, for
> (I believe) exactly the same reasons as I mention below. While I'm sure
> it could theoretically be nice for them to be able to use
> drivers/pci/pwrctrl/, I expect they cannot today, for the same reasons.
> 

If you look into brcm_pcie_add_bus(), they are ignoring the return value of
brcm_pcie_start_link() precisely for the reason I explained in the previous
thread. However, they do check for it in brcm_pcie_resume_noirq() which looks
like a bug as the controller will fail to resume from system suspend if no
devices are connected.

- Mani

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