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). So without this check the capability gets disabled on boot. > > > + 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) > > -- David
