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

[Bjorn Helgaas]

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 at 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.

Bjorn