RE: [PATCH v4 2/2] PCI/PM: Fix pci_pm_suspend_noirq() to disable PTM

["Jingar, Rajvi" <rajvi.jingar@intel.com>]

> -----Original Message-----
> From: Bjorn Helgaas <helgaas@kernel.org>
> Sent: Friday, April 22, 2022 3:25 PM
> To: Jingar, Rajvi <rajvi.jingar@intel.com>
> Cc: bhelgaas@google.com; david.e.box@linux.intel.com; linux-
> pci@vger.kernel.org; linux-kernel@vger.kernel.org; linux-pm@vger.kernel.org;
> Wysocki, Rafael J <rafael.j.wysocki@intel.com>; Kai-Heng Feng
> <kai.heng.feng@canonical.com>; mika.westerberg@linux.intel.com;
> koba.ko@canonical.com; baolu.lu@linux.intel.com;
> sathyanarayanan.kuppuswamy@linux.intel.com; Russell Currey
> <ruscur@russell.cc>; Oliver O'Halloran <oohall@gmail.com>; linuxppc-
> dev@lists.ozlabs.org
> Subject: Re: [PATCH v4 2/2] PCI/PM: Fix pci_pm_suspend_noirq() to disable PTM
> 
> [+cc other folks interested in PTM from
> https://lore.kernel.org/r/20220408153159.106741-1-
> kai.heng.feng@canonical.com]
> 
> On Thu, Apr 14, 2022 at 07:54:02PM +0200, Rafael J. Wysocki wrote:
> > On 3/25/2022 8:50 PM, Rajvi Jingar wrote:
> > > For the PCIe devices (like nvme) that do not go into D3 state still need to
> > > disable PTM on PCIe root ports 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 patch 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.
> > >
> > > Fixes: a697f072f5da ("PCI: Disable PTM during suspend to save power")
> > > Signed-off-by: Rajvi Jingar <rajvi.jingar@intel.com>
> > > Suggested-by: David E. Box <david.e.box@linux.intel.com>
> 
> > > ---
> > >   v1 -> v2: add Fixes tag in commit message
> > >   v2 -> v3: move changelog after "---" marker
> > >   v3 -> v4: add "---" marker after changelog
> > > ---
> > >   drivers/pci/pci-driver.c | 10 ++++++++++
> > >   drivers/pci/pci.c        | 10 ----------
> > >   2 files changed, 10 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > > index 8b55a90126a2..ab733374a260 100644
> > > --- a/drivers/pci/pci-driver.c
> > > +++ b/drivers/pci/pci-driver.c
> > > @@ -847,6 +847,16 @@ static int pci_pm_suspend_noirq(struct device *dev)
> > >   	if (!pci_dev->state_saved) {
> > >   		pci_save_state(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 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.
> > > +		 */
> > > +		if (pci_pcie_type(pci_dev) == PCI_EXP_TYPE_ROOT_PORT)
> > > +			pci_disable_ptm(pci_dev);
> 
> Why is disabling PTM dependent on pci_dev->state_saved?  The point of
> this is to change the behavior of the device, and it seems like we
> want to do that regardless of whether the driver has used
> pci_save_state().
> 

Because we use the saved state to restore PTM on the root port. 
And it's under this condition that the root port state gets saved.

> Bjorn