Re: [PATCH] PCI: Save/restore L1 PM Substate extended capability registers

[David E. Box]

Great. Thanks Vidya.

On Wed, 2020-12-09 at 09:38 +0530, Vidya Sagar wrote:
> There is a change already available for it in linux-next
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=4257f7e008ea394fcecc050f1569c3503b8bcc15
> 
> Thanks,
> Vidya Sagar
> 
> On 12/9/2020 3:36 AM, David E. Box wrote:
> > External email: Use caution opening links or attachments
> > 
> > 
> > On Intel systems that support ACPI Low Power Idle it has been
> > observed
> > that the L1 Substate capability can return disabled after a s2idle
> > cycle. This causes the loss of L1 Substate support during runtime
> > leading to higher power consumption. Add save/restore of the L1SS
> > control registers.
> > 
> > Signed-off-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/pci/pci.c | 49
> > +++++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 49 insertions(+)
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index e578d34095e9..beee3d9952a6 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -1539,6 +1539,48 @@ static void pci_restore_ltr_state(struct
> > pci_dev *dev)
> >          pci_write_config_word(dev, ltr + PCI_LTR_MAX_NOSNOOP_LAT,
> > *cap++);
> >   }
> > 
> > +static void pci_save_l1ss_state(struct pci_dev *dev)
> > +{
> > +       int l1ss;
> > +       struct pci_cap_saved_state *save_state;
> > +       u16 *cap;
> > +
> > +       if (!pci_is_pcie(dev))
> > +               return;
> > +
> > +       l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
> > +       if (!l1ss)
> > +               return;
> > +
> > +       save_state = pci_find_saved_ext_cap(dev,
> > PCI_EXT_CAP_ID_L1SS);
> > +       if (!save_state) {
> > +               pci_err(dev, "no suspend buffer for L1
> > Substates\n");
> > +               return;
> > +       }
> > +
> > +       cap = (u16 *)&save_state->cap.data[0];
> > +       pci_read_config_word(dev, l1ss + PCI_L1SS_CTL1, cap++);
> > +       pci_read_config_word(dev, l1ss + PCI_L1SS_CTL1 + 2, cap++);
> > +       pci_read_config_word(dev, l1ss + PCI_L1SS_CTL2, cap++);
> > +}
> > +
> > +static void pci_restore_l1ss_state(struct pci_dev *dev)
> > +{
> > +       struct pci_cap_saved_state *save_state;
> > +       int l1ss;
> > +       u16 *cap;
> > +
> > +       save_state = pci_find_saved_ext_cap(dev,
> > PCI_EXT_CAP_ID_L1SS);
> > +       l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
> > +       if (!save_state || !l1ss)
> > +               return;
> > +
> > +       cap = (u16 *)&save_state->cap.data[0];
> > +       pci_write_config_word(dev, l1ss + PCI_L1SS_CTL1, *cap++);
> > +       pci_write_config_word(dev, l1ss + PCI_L1SS_CTL1 + 2,
> > *cap++);
> > +       pci_write_config_word(dev, l1ss + PCI_L1SS_CTL2, *cap++);
> > +}
> > +
> >   /**
> >    * pci_save_state - save the PCI configuration space of a device
> > before
> >    *                 suspending
> > @@ -1563,6 +1605,7 @@ int pci_save_state(struct pci_dev *dev)
> >          if (i != 0)
> >                  return i;
> > 
> > +       pci_save_l1ss_state(dev);
> >          pci_save_ltr_state(dev);
> >          pci_save_dpc_state(dev);
> >          pci_save_aer_state(dev);
> > @@ -1670,6 +1713,7 @@ void pci_restore_state(struct pci_dev *dev)
> >           */
> >          pci_restore_ltr_state(dev);
> > 
> > +       pci_restore_l1ss_state(dev);
> >          pci_restore_pcie_state(dev);
> >          pci_restore_pasid_state(dev);
> >          pci_restore_pri_state(dev);
> > @@ -3332,6 +3376,11 @@ void pci_allocate_cap_save_buffers(struct
> > pci_dev *dev)
> >          if (error)
> >                  pci_err(dev, "unable to allocate suspend buffer
> > for LTR\n");
> > 
> > +       error = pci_add_ext_cap_save_buffer(dev,
> > PCI_EXT_CAP_ID_L1SS,
> > +                                           3 * sizeof(u16));
> > +       if (error)
> > +               pci_err(dev, "unable to allocate suspend buffer for
> > L1 Substates\n");
> > +
> >          pci_allocate_vc_save_buffers(dev);
> >   }
> > 
> > --
> > 2.20.1
> >