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

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Date:   Sat, 16 Dec 2017 00:44:03 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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 <y.c.chen@...el.com>
Subject: Re: [PATCH] PCI / PM: Force devices to D0 in pci_pm_thaw_noirq()

On Fri, Dec 15, 2017 at 7:30 PM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> On Fri, Dec 15, 2017 at 03:07:18AM +0100, Rafael J. Wysocki 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>
>
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
>
> Let me know if you want me to take this.  I don't have anything
> currently queued up that touches pci-driver.c, so I'm happy if you
> take it yourself.

I will take it.

Depending of what Yu finds, we may need an additional fix to make the
Purley system work.

>> ---
>>
>> 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.
>>
>> ---
>>  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)
>>