On Thu, Nov 19, 2020 at 6:45 PM David E. Box <david.e.box@xxxxxxxxxxxxxxx> wrote: > > On Thu, 2020-11-19 at 13:01 +0100, Rafael J. Wysocki wrote: > > On Thu, Nov 19, 2020 at 1:17 AM David E. Box > > <david.e.box@xxxxxxxxxxxxxxx> wrote: > > > On Intel client platforms that support suspend-to-idle, like Ice > > > Lake, > > > root ports that have Precision Time Management (PTM) enabled can > > > prevent > > > the port from being fully power gated, causing higher power > > > consumption > > > while suspended. To prevent this, after saving the PTM control > > > register, > > > disable the feature. The feature will be returned to its previous > > > state > > > during restore. > > > > > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=209361 > > > Reported-by: Len Brown <len.brown@xxxxxxxxx> > > > Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > > Signed-off-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx> > > > --- > > > drivers/pci/pci.c | 14 +++++++++++++- > > > 1 file changed, 13 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > > > index 6fd4ae910a88..a2b40497d443 100644 > > > --- a/drivers/pci/pci.c > > > +++ b/drivers/pci/pci.c > > > @@ -21,6 +21,7 @@ > > > #include <linux/module.h> > > > #include <linux/spinlock.h> > > > #include <linux/string.h> > > > +#include <linux/suspend.h> > > > #include <linux/log2.h> > > > #include <linux/logic_pio.h> > > > #include <linux/pm_wakeup.h> > > > @@ -1543,7 +1544,7 @@ static void pci_save_ptm_state(struct pci_dev > > > *dev) > > > { > > > int ptm; > > > struct pci_cap_saved_state *save_state; > > > - u16 *cap; > > > + u16 *cap, ctrl; > > > > > > if (!pci_is_pcie(dev)) > > > return; > > > @@ -1560,6 +1561,17 @@ static void pci_save_ptm_state(struct > > > pci_dev *dev) > > > > > > cap = (u16 *)&save_state->cap.data[0]; > > > pci_read_config_word(dev, ptm + PCI_PTM_CTRL, cap); > > > + > > > + /* > > > + * On Intel systems that support suspend-to-idle, > > > additional > > > + * power savings can be gained by disabling PTM on root > > > ports, > > > + * as this allows the port to enter a deeper pm state. > > > > I would say "There are systems (for example, ...) where the power > > drawn while suspended can be significantly reduced by disabling PTM > > on > > PCIe root ports, as this allows the port to enter a lower-power PM > > state and the SoC to reach a lower-power idle state as a whole". > > Okay. > > > > > > + */ > > > + if (pm_suspend_target_state == PM_SUSPEND_TO_IDLE && > > > > AFAICS the target sleep state doesn't matter here, so I'd skip the > > check above, but otherwise it LGTM. > > The target sleep state doesn't matter so much but that it's suspending > does. pci_save_state() is called during probe for the root ports (and > many other pci devices - I'm curious as to why). I tend to forget about this, sorry. > So without this check the capability gets disabled on boot. > So instead of calling this from here, why don't we invoke the code below from pci_prepare_to_sleep() and pci_finish_runtime_suspend(), before enabling wakeup (and it needs to be re-done on failures, eg. by restoring the cap from the saved copy)? > > > + pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT) { > > > + ctrl = *cap & ~(PCI_PTM_CTRL_ENABLE | > > > PCI_PTM_CTRL_ROOT); > > > + pci_write_config_word(dev, ptm + PCI_PTM_CTRL, > > > ctrl); > > > + } > > > } > > > > > > static void pci_restore_ptm_state(struct pci_dev *dev) > > > --
