On Thu, May 12, 2022 at 7:42 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > Hi Rajvi, > > I received your v1, v2, v3, v4, v5 postings because they were sent > directly to bhelgaas@xxxxxxxxxx, but for some reason vger doesn't like > them so they don't show up on the mailing list: > > https://lore.kernel.org/all/?q=a%3Arajvi.jingar > > I looked at the ones I received directly and don't see an obvious > problem. Maybe there's a hint here? > > http://vger.kernel.org/majordomo-info.html > > All patches should appear on the linux-pci mailing list before > applying them, so we need to figure this out somehow. In fact, I read > and review patches from linux-pci, so I often don't even see things > that are just sent directly to bhelgaas@xxxxxxxxxx. > > On Thu, May 12, 2022 at 03:49:18PM +0200, Rafael J. Wysocki wrote: > > On 4/29/2022 11:05 PM, Rajvi Jingar wrote: > > > For the PCIe devices (like nvme) that do not go into D3 state still need to > > > disable PTM to allow the port to enter a lower-power PM state and the SoC > > > to reach a lower-power idle state as a whole. Move the pci_disable_ptm() > > > out of pci_prepare_to_sleep() as this code path is not followed for devices > > > that do not go into D3. This fixes the issue seen on Dell XPS 9300 with > > > Ice Lake CPU and Dell Precision 5530 with Coffee Lake CPU platforms to get > > > improved residency in low power idle states. > > I think the paragraph above is a distraction, and the real reason is > the paragraph below. > > > > Also, on receiving a PTM Request from a downstream device, if PTM is > > > disabled on the root port, as per PCIe r6.0, sec 6.21.3, such a request > > > would cause an Unsupported Request error. So it must first disable PTM in > > > any downstream devices. > > > > > > Fixes: a697f072f5da ("PCI: Disable PTM during suspend to save power") > > > Signed-off-by: Rajvi Jingar <rajvi.jingar@xxxxxxxxx> > > > Suggested-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx> > > > --- > > > v1 -> v2: add Fixes tag in commit message > > > v2 -> v3: move changelog after "---" marker > > > v3 -> v4: add "---" marker after changelog > > > v4 -> v5: move pci_disable_ptm() out of the pci_dev->state_saved check. > > > disable PTM for all devices, not just root ports. > > > --- > > > drivers/pci/pci-driver.c | 28 +++++++++++++++++++--------- > > > drivers/pci/pci.c | 10 ---------- > > > 2 files changed, 19 insertions(+), 19 deletions(-) > > > > > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c > > > index 8b55a90126a2..400dd18a9cf5 100644 > > > --- a/drivers/pci/pci-driver.c > > > +++ b/drivers/pci/pci-driver.c > > > @@ -813,6 +813,7 @@ static int pci_pm_suspend_late(struct device *dev) > > > static int pci_pm_suspend_noirq(struct device *dev) > > > { > > > + unsigned int dev_state_saved; > > > struct pci_dev *pci_dev = to_pci_dev(dev); > > > const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL; > > > @@ -845,16 +846,25 @@ static int pci_pm_suspend_noirq(struct device *dev) > > > } > > > } > > > - if (!pci_dev->state_saved) { > > > + dev_state_saved = pci_dev->state_saved; > > > > If pci_dev->state_saved is set here, the device may be in D3cold already and > > disabling PTM for it will not work. Of course, it is not necessary to > > disable PTM for it then, but this case need to be taken care of. > > > > > + if (!dev_state_saved) > > > pci_save_state(pci_dev); > > > - /* > > > - * If the device is a bridge with a child in D0 below it, it needs to > > > - * stay in D0, so check skip_bus_pm to avoid putting it into a > > > - * low-power state in that case. > > > - */ > > > - if (!pci_dev->skip_bus_pm && pci_power_manageable(pci_dev)) > > > - pci_prepare_to_sleep(pci_dev); > > > - } > > > + > > > + /* > > > + * There are systems (for example, Intel mobile chips since Coffee > > > + * Lake) where the power drawn while suspended can be significantly > > > + * reduced by disabling PTM as this allows the SoC to reach a > > > + * lower-power idle state as a whole. > > I think the argument for disabling PTM is that: > > - If a PTM Requester is put in a low-power state, a PTM Responder > upstream from it may also be put in a low-power state. > > - Putting a Port in D1, D2, or D3hot does not prohibit it from > sending or responding to PTM Requests (I'd be glad to be corrected > about this). > > - We want to disable PTM on Responders when they are in a low-power > state. > > - Per 6.21.3, a PTM Requester must not be enabled when the upstream > PTM Responder is disabled. > > - Therefore, we must disable all PTM on all downstream PTM > Requesters before disabling it on the PTM Responder, e.g., a Root > Port. > > This has nothing specifically to do with Coffee Lake or other Intel > chips, so I think the comment should be merely something to the > effect that "disabling PTM reduces power consumption." > > > Something like this should suffice IMV: > > > > if (!dev_state_saved || pci_dev->current_state != PCI_D3cold) > > > > pci_disable_ptm(pci_dev); > > It makes sense to me that we needn't disable PTM if the device is in > D3cold. But the "!dev_state_saved" condition depends on what the > driver did. Why is that important? Why should we not do the > following? > > if (pci_dev->current_state != PCI_D3cold) > pci_disable_ptm(pci_dev); We can do this too. I thought we could skip the power state check if dev_state_saved was unset, because then we would know that the power state was not D3cold. It probably isn't worth the hassle though.
