Re: [PATCH V3] PCI/ASPM: Save/restore L1SS Capability for suspend/resume

[Vidya Sagar]

On 9/8/2022 2:35 AM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
>
>
> On Fri, Aug 26, 2022 at 06:25:26PM +0530, Vidya Sagar wrote:
> > Previously ASPM L1 Substates control registers (CTL1 and CTL2) weren't
> > saved and restored during suspend/resume leading to L1 Substates
> > configuration being lost post-resume.
> >
> > Save the L1 Substates control registers so that the configuration is
> > retained post-resume.
> >
> > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> > ---
> > V3:
> > * Disabled L1.2 enable fields while restoring Control-1 register
>
> This really looks promising!  Has somebody confirmed that the
> disappearing L1SS capability problem doesn't happen here?

Based on the update from Lukasz in 
https://patchwork.kernel.org/project/linux-pci/patch/20220705060014.10050-1-vidyas@xxxxxxxxxx/ 
(last update), the L1SS capability registers disappearing issue is not 
due to this change and they are working on it seems.

> > +void pci_save_aspm_l1ss_state(struct pci_dev *dev)
> > +{
> > +     int aspm_l1ss;
> > +     struct pci_cap_saved_state *save_state;
> > +     u32 *cap;
> > +
> > +     if (!pci_is_pcie(dev))
> > +             return;
> > +
> > +     aspm_l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
> > +     if (!aspm_l1ss)
> > +             return;
>
> Isn't it enough to check this?

Yup. I'll address it in the next version.

>    if (!dev->l1ss)
>      return;
>
> > +void pci_restore_aspm_l1ss_state(struct pci_dev *dev)
> > +{
> > +     int aspm_l1ss;
> > +     struct pci_cap_saved_state *save_state;
> > +     u32 *cap, l1_2_enable;
> > +
> > +     if (!pci_is_pcie(dev))
> > +             return;
> > +
> > +     aspm_l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
> > +     if (!aspm_l1ss)
> > +             return;
> > +
> > +     save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_L1SS);
> > +     if (!save_state)
> > +             return;
> > +
> > +     cap = (u32 *)&save_state->cap.data[0];
> > +     pci_write_config_dword(dev, aspm_l1ss + PCI_L1SS_CTL2, *cap++);
> > +     /* Disable L1.2 while updating.  See PCIe r5.0, sec 5.5.4, 7.8.3.3 */
> > +     l1_2_enable = *cap & PCI_L1SS_CTL1_L1_2_MASK;
> > +     pci_write_config_dword(dev, aspm_l1ss + PCI_L1SS_CTL1,
> > +                            (*cap & ~PCI_L1SS_CTL1_L1_2_MASK));
> > +     if (l1_2_enable)
> > +             pci_clear_and_set_dword(dev, aspm_l1ss + PCI_L1SS_CTL1, 0,
> > +                                     l1_2_enable);
> > +}
>
> What if we did something like the following?  Then we wouldn't have to
> duplicate the fancy logic in aspm_calc_l1ss_info() and
> pci_restore_aspm_l1ss_state(), and we'd only need the big comment in
> one place.

I'll refactor the existing code accommodating this suggestion and push 
L1SS save/restore change on top of it in the next version.

Thanks for your review comments.

> +static void aspm_program_l1ss(struct pci_dev *dev, u32 ctl1, u32 ctl2)
> +{
> +       u16 l1ss = dev->l1ss;
> +       u32 l1_2_enable;
> +
> +       /*
> +        * Per PCIe r6.0, sec 5.5.4, T_POWER_ON in PCI_L1SS_CTL2 must be
> +        * programmed prior to setting the L1.2 enable bits in PCI_L1SS_CTL1.
> +        */
> +       pci_write_config_dword(dev, l1ss + PCI_L1SS_CTL2, ctl2);
> +
> +       /*
> +        * In addition, Common_Mode_Restore_Time and LTR_L1.2_THRESHOLD in
> +        * PCI_L1SS_CTL1 must be programmed *before* setting the L1.2
> +        * enable bits, even though they're all in PCI_L1SS_CTL1.
> +        */
> +       l1_2_enable = ctl1 & PCI_L1SS_CTL1_L1_2_MASK;
> +       ctl1 &= ~PCI_L1SS_CTL1_L1_2_MASK;
> +
> +       pci_write_config_dword(dev, l1ss + PCI_L1SS_CTL1, ctl1);
> +       if (l1_2_enable)
> +               pci_write_config_dword(dev, l1ss + PCI_L1SS_CTL1,
> +                                      ctl1 | l1_2_enable);
> +}
>
> (This is somewhat simplified from what aspm_calc_l1ss_info() does
> today.  It looks to me like aspm_calc_l1ss_info() does more config
> reads than necessary.)