RE: [PATCH v5 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: Thursday, May 12, 2022 11:36 AM
> To: Rafael J. Wysocki <rafael@kernel.org>
> Cc: Jingar, Rajvi <rajvi.jingar@intel.com>; Wysocki, Rafael J
> <rafael.j.wysocki@intel.com>; Bjorn Helgaas <bhelgaas@google.com>; David Box
> <david.e.box@linux.intel.com>; Linux PCI <linux-pci@vger.kernel.org>; Linux
> Kernel Mailing List <linux-kernel@vger.kernel.org>; Linux PM <linux-
> pm@vger.kernel.org>
> Subject: Re: [PATCH v5 2/2] PCI/PM: Fix pci_pm_suspend_noirq() to disable PTM
> 
> On Thu, May 12, 2022 at 07:52:36PM +0200, Rafael J. Wysocki wrote:
> > On Thu, May 12, 2022 at 7:42 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > On Thu, May 12, 2022 at 03:49:18PM +0200, Rafael J. Wysocki wrote:
> 
> > > > 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.
>

We see issue with certain platforms where only checking if device power 
state in D3Cold is not enough and the !dev_state_saved check is needed
when disabling PTM. Device like nvme is relying on ASPM, it stays in D0 but 
state is saved. Touching the config space wakes up the device which 
prevents the system from entering into low power state.

Following would fix the issue:

 if (!pci_dev->state_save) {
                pci_save_state(pci_dev);

               pci_disable_ptm(pci_dev);

                if (!pci_dev->skip_bus_pm && pci_power_manageable(pci_dev))
                        pci_prepare_to_sleep(pci_dev);
}

> Ah, thanks.  IMHO it's easier to analyze for correctness if we only
> check the power state.
> 
> Bjorn