linux-kernel - Re: [PATCH v5 2/2] PCI/PM: Fix pci_pm_suspend

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Date:   Sat, 14 May 2022 19:12:43 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Jingar, Rajvi" <rajvi.jingar@...el.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        David Box <david.e.box@...ux.intel.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v5 2/2] PCI/PM: Fix pci_pm_suspend_noirq() to disable PTM

On Sat, May 14, 2022 at 12:01 AM Jingar, Rajvi <rajvi.jingar@...el.com> wrote:
>
>
> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@...nel.org>
> > Sent: Thursday, May 12, 2022 11:36 AM
> > To: Rafael J. Wysocki <rafael@...nel.org>
> > Cc: Jingar, Rajvi <rajvi.jingar@...el.com>; Wysocki, Rafael J
> > <rafael.j.wysocki@...el.com>; Bjorn Helgaas <bhelgaas@...gle.com>; David Box
> > <david.e.box@...ux.intel.com>; Linux PCI <linux-pci@...r.kernel.org>; Linux
> > Kernel Mailing List <linux-kernel@...r.kernel.org>; Linux PM <linux-
> > pm@...r.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@...nel.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);
> }

Well, the point is to also disable PTM for devices that were put into
D3 by their drivers.

In addition to D3cold, the check could cover D0 too, that is

if (pci_dev->current_state > D0 && pci_dev->current_state < PCI_D3cold)
         pci_disable_ptm(pci_dev);

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