Re: [PATCH V1] PCI/ASPM: Save/restore L1SS Capability for suspend/resume

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Apr 21, 2022 at 02:16:29PM +0800, Kai-Heng Feng wrote:
> On Sat, Apr 16, 2022 at 5:25 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Fri, Apr 15, 2022 at 10:26:19PM +0800, Kai-Heng Feng wrote:
> > ...

> > > So I forced the pcie_aspm_pm_state_change() calling path to eventually
> > > call aspm_calc_l1ss_info() which solved the problem for me.
> >
> > This would update T_PwrOn and LTR1.2_Threshold, so I guess it makes
> > sense that this would help.  But I think we need to figure out the
> > reason why pcie_aspm_pm_state_change() exists and get rid of it or at
> > least better integrate it with pci_restore_state().
> >
> > If we call pcie_aspm_pm_state_change() after D3cold or reset, things
> > still aren't going to work because the LTR cap isn't restored or
> > programmed.
> 
> More than that, the ASPM sysfs won't be restored correctly after
> resume [1] because of it.
> So I'd like to post a patch to drop pcie_aspm_pm_state_change() if
> there's no objection.

Please do :)  Obviously somebody thought we needed
pcie_aspm_pm_state_change() for some reason or it wouldn't have been
added.  But I didn't figure out since it was included in the very
first ASPM support: 6c723d5bd89f ("PCI: PCIE ASPM support").

Maybe the comment that "devices changed PM state, we should recheck if
latency meets all functions' requirement" is a clue but I haven't
followed up.

> [1] https://lore.kernel.org/linux-pci/20211021035159.1117456-2-kai.heng.feng@canonical.com/
> 
> Kai-Heng