Re: [PATCH V4] PCI/ASPM: Update saved buffers with latest ASPM

["David E. Box" <david.e.box@linux.intel.com>]

On Tue, 2024-03-05 at 16:03 -0600, Bjorn Helgaas wrote:
> [+to Sathy, David in case you want to update your Reviewed-by]
> 
> On Thu, Feb 22, 2024 at 11:14:36PM +0530, Vidya Sagar wrote:
> > Many PCIe device drivers save the configuration state of their respective
> > devices during probe and restore the same when their 'slot_reset' hook
> > is called through PCIe Error Recovery Handler.
> > 
> > If the system has a change in ASPM policy after the driver's probe is
> > called and before error event occurred, 'slot_reset' hook restores the
> > PCIe configuration state to what it was at the time of probe but not to
> > what it was just before the occurrence of the error event.
> > This effectively leads to a mismatch in the ASPM configuration between
> > the device and its upstream parent device.
> > 
> > Update the saved configuration state of the device with the latest info
> > whenever there is a change w.r.t ASPM policy.
> > 
> > Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> 
> > -void pci_save_aspm_state(struct pci_dev *pdev);
> > +void pci_save_aspm_l1ss_state(struct pci_dev *pdev);
> 
> I rebased this again on top of my pci/aspm updates to remove the need
> for the rename above.
> 
> > +static void pci_save_aspm_state(struct pci_dev *dev)
> > +{
> > +       struct pci_cap_saved_state *save_state;
> > +       u16 *cap;
> > +
> > +       if (!pci_is_pcie(dev))
> > +               return;
> > +
> > +       save_state = pci_find_saved_cap(dev, PCI_CAP_ID_EXP);
> > +       if (!save_state)
> > +               return;
> > +
> > +       cap = (u16 *)&save_state->cap.data[0];
> > +       pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &cap[1]);
> 
> And I changed this part so it only updates the PCI_EXP_LNKCTL_ASPMC
> bits, not the entire LNKCTL.
> 
> Updating the entire saved register probably wouldn't *break* anything,
> but it could randomly hide other LNKCTL changes depending on whether
> or not ASPM configuration was changed in the interim.  For example:
> 
>   - driver .probe() saves LNKCTL
>   - LNKCTL changes some non-ASPMC thing via setpci or other mechanism
>   - save_state updated via pcie_config_aspm_link()
> 
> A restore in .slot_reset() would restore different LNKCTL values for
> the non-ASPMC change depending on whether pcie_config_aspm_link() was
> used.
> 
> I applied it on pci/aspm for v6.9.  Please take a look and make sure
> it still does what you need:
> https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=aspm&id=a6315434436d587f70e489e6365c5b7e20176a71
> 
> Sathy and David, I didn't add your Reviewed-by because I didn't want
> to presume that you were OK with my changes.  But I'd be more than
> happy to add them if you take a look.
> 
> Bjorn
> 
> > +}
> > +
> >  void pci_aspm_get_l1ss(struct pci_dev *pdev)
> >  {
> >         /* Read L1 PM substate capabilities */
> >         pdev->l1ss = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_L1SS);
> >  }
> >  
> > -void pci_save_aspm_state(struct pci_dev *pdev)
> > +void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
> >  {
> >         struct pci_cap_saved_state *save_state;
> >         u16 l1ss = pdev->l1ss;
> > @@ -309,10 +325,12 @@ static void pcie_set_clkpm_nocheck(struct
> > pcie_link_state *link, int enable)
> >         struct pci_bus *linkbus = link->pdev->subordinate;
> >         u32 val = enable ? PCI_EXP_LNKCTL_CLKREQ_EN : 0;
> >  
> > -       list_for_each_entry(child, &linkbus->devices, bus_list)
> > +       list_for_each_entry(child, &linkbus->devices, bus_list) {
> >                 pcie_capability_clear_and_set_word(child, PCI_EXP_LNKCTL,
> >                                                    PCI_EXP_LNKCTL_CLKREQ_EN,
> >                                                    val);
> > +               pci_save_aspm_state(child);
> > +       }
> >         link->clkpm_enabled = !!enable;
> >  }
> >  
> > @@ -931,6 +949,12 @@ static void pcie_config_aspm_link(struct
> > pcie_link_state *link, u32 state)
> >                 pcie_config_aspm_dev(parent, upstream);
> >  
> >         link->aspm_enabled = state;
> > +
> > +       /* Update latest ASPM configuration in saved context */
> > +       pci_save_aspm_state(link->downstream);
> > +       pci_save_aspm_l1ss_state(link->downstream);
> > +       pci_save_aspm_state(parent);
> > +       pci_save_aspm_l1ss_state(parent);
> >  }
> >  
> >  static void pcie_config_aspm_path(struct pcie_link_state *link)
> > -- 
> > 2.25.1
> > 

Reviewed-by: David E. Box <david.e.box@linux.intel.com>