linux-kernel - Re: [PATCH] PCI / PM: Force devices to D0 in pci_pm_thaw

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Message-ID: <CAJZ5v0i1g2GJsfd_tPvtiFT0P=c_MPHkKDKLgSgiFK+CCcieEA@mail.gmail.com>
Date:   Fri, 15 Dec 2017 15:28:11 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Maarten Lankhorst <dev@...ankhorst.nl>,
        Michal Hocko <mhocko@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Chen Yu <yu.c.chen@...el.com>
Subject: Re: [PATCH] PCI / PM: Force devices to D0 in pci_pm_thaw_noirq()

On Fri, Dec 15, 2017 at 3:07 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> It is incorrect to call pci_restore_state() for devices in low-power
> states (D1-D3), as that involves the restoration of MSI setup which
> requires MMIO to be operational and that is only the case in D0.
>
> However, pci_pm_thaw_noirq() may do that if the driver's "freeze"
> callbacks put the device into a low-power state, so fix it by making
> it force devices into D0 via pci_set_power_state() instead of trying
> to "update" their power state which is pointless.
>
> Fixes: e60514bd4485 (PCI/PM: Restore the status of PCI devices across hibernation)
> Cc: 4.13+ <stable@...r.kernel.org> # 4.13+
> Reported-by: Thomas Gleixner <tglx@...utronix.de>
> Reported-by: Maarten Lankhorst <dev@...ankhorst.nl>
> Tested-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Maarten Lankhorst <dev@...ankhorst.nl>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>
> The bug is not as old as I thought, actually.
>
> Yes, we did the pci_update_current_state() in pci_pm_thaw_noirq()
> forever, but it started to be problematic in 4.13, when we started
> to call pci_restore_state() in addition to it to fix another issue.

Bjorn, any concerns about this one?

> ---
>  drivers/pci/pci-driver.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> Index: linux-pm/drivers/pci/pci-driver.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-driver.c
> +++ linux-pm/drivers/pci/pci-driver.c
> @@ -1027,7 +1027,12 @@ static int pci_pm_thaw_noirq(struct devi
>         if (pci_has_legacy_pm_support(pci_dev))
>                 return pci_legacy_resume_early(dev);
>
> -       pci_update_current_state(pci_dev, PCI_D0);
> +       /*
> +        * pci_restore_state() requires the device to be in D0 (because of MSI
> +        * restoration among other things), so force it into D0 in case the
> +        * driver's "freeze" callbacks put it into a low-power state directly.
> +        */
> +       pci_set_power_state(pci_dev, PCI_D0);
>         pci_restore_state(pci_dev);
>
>         if (drv && drv->pm && drv->pm->thaw_noirq)
>