Re: [PATCH v2 1/4] PCI: dwc: Advertise L1 PM Substates only if driver requests it

Manivannan Sadhasivam
2025-11-25T05:25:33Z

On Mon, Nov 24, 2025 at 03:19:03PM -0600, Bjorn Helgaas wrote:
> On Thu, Nov 20, 2025 at 01:10:56PM +0530, Manivannan Sadhasivam wrote:
> > On Tue, Nov 18, 2025 at 03:42:15PM -0600, Bjorn Helgaas wrote:
> > > From: Bjorn Helgaas <bhelgaas@google.com>
> > >
> > > L1 PM Substates require the CLKREQ# signal and may also require
> > > device-specific support. If CLKREQ# is not supported or driver support is
> > > lacking, enabling L1.1 or L1.2 may cause errors when accessing devices,
> > > e.g.,
> > >
> > > nvme nvme0: controller is down; will reset: CSTS=0xffffffff, PCI_STATUS=0x10
> > >
> > > If the kernel is built with CONFIG_PCIEASPM_POWER_SUPERSAVE=y or users
> > > enable L1.x via sysfs, users may trip over these errors even if L1
> > > Substates haven't been enabled by firmware or the driver.
> > >
> > > To prevent such errors, disable advertising the L1 PM Substates unless the
> > > driver sets "dw_pcie.l1ss_support" to indicate that it knows CLKREQ# is
> > > present and any device-specific configuration has been done.
> >
> > Going by this reasoning, why can't we enable L1 PM Substates for
> > these platforms by default?
>
> I think we can, in a separate series. I don't have time to deal with
> this before the v6.19 merge window, but you can certainly do that.
>

I will take it up. Not sure if I can do it for v6.19 though.

- Mani

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