Re: [PATCH 4/8] PCI: dwc: qcom: Update ICC & OPP votes based upon the requested speed

From: Bjorn Helgaas
Date: Wed Feb 19 2025 - 13:34:39 EST


On Wed, Feb 19, 2025 at 11:28:47PM +0530, Krishna Chaitanya Chundru wrote:
> On 2/19/2025 3:37 AM, Bjorn Helgaas wrote:
> > On Mon, Feb 17, 2025 at 12:04:11PM +0530, Krishna Chaitanya Chundru wrote:
> > > QCOM PCIe controllers needs to disable ASPM before initiating link
> > > re-train. So as part of pre_bw_scale() disable ASPM and as part of
> > > post_scale_bus_bw() enable ASPM back.
> >
> > s/needs/need/
> >
> > Why does Qcom need to disable ASPM? Is there a PCIe spec restriction
> > about this that should be applied to all PCIe host bridges? Or is
> > this a Qcom defect?
> >
> It is QCOM controller issue, PCIe spec doesn't mention to disable ASPM.

OK. I'm a little concerned that disabling/enabling
PCIE_LINK_STATE_ALL might clobber preferences set by drivers of
downstream devices, but I guess ...

Maybe we could add a comment in the code about this being done to work
around some Qcom issue so that browsers of
pci_enable_link_state_locked() don't get the idea that this needs to
be done generically.

Bjorn