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Date: Wed, 10 Nov 2021 08:14:39 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Robert Święcki <robert@...ecki.net>
Cc: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>,
linux-i2c <linux-i2c@...r.kernel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Linux PCI <linux-pci@...r.kernel.org>,
Linux PM <linux-pm@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH] pci: Don't call resume callback for nearly bound devices
On Tue, Nov 09, 2021 at 02:05:18PM -0600, Bjorn Helgaas wrote:
> On Tue, Nov 09, 2021 at 07:58:47PM +0100, Rafael J. Wysocki wrote:
> > On Tue, Nov 9, 2021 at 7:52 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > > ...
> > > So instead, we can drop the pm_runtime_get_sync() and
> > > pm_runtime_put_sync() from local_pci_probe() and pci_device_remove(),
> > > respectively, and add pm_runtine_get_noresume() to pci_pm_init(),
> > > which will prevent PM-runtime from touching the device until it has a
> > > driver that supports PM-runtime.
> > >
> > > We'll lose the theoretical ability to put unbound devices into D3 this
> > > way, but we learned some time ago that this isn't safe in all cases
> > > anyway.
> >
> > IOW, something like this (untested and most likely white-space-damaged).
>
> Thanks! I applied this manually to for-linus in hopes of making the
> the next linux-next build.
>
> Please send any testing reports and corrections to the patch and
> commit log!
Robert, I hate to ask even more of you, but if you have a chance, it
would be very helpful if you could test the patch below. I'm pretty
sure it should fix the problem you saw, and I hope to ask Linus to
merge it today.
> commit dd414877b58b ("PCI/PM: Prevent runtime PM until claimed by a driver that supports it")
> Author: Bjorn Helgaas <bhelgaas@...gle.com>
> Date: Tue Nov 9 13:36:09 2021 -0600
>
> PCI/PM: Prevent runtime PM until claimed by a driver that supports it
>
> Previously we had a path that could call a driver's ->runtime_resume()
> method before calling the driver's ->probe() method, which is a problem
> because ->runtime_resume() often relies on initialization done in
> ->probe():
>
> local_pci_probe
> pm_runtime_get_sync
> ...
> pci_pm_runtime_resume
> if (!pci_dev->driver)
> return 0; <-- early exit
> dev->driver->pm->runtime_resume(); <-- driver ->runtime_resume()
> pci_dev->driver = pci_drv;
> pci_drv->probe() <-- driver ->probe()
>
> Prior to 2a4d9408c9e8 ("PCI: Use to_pci_driver() instead of
> pci_dev->driver"), we took the early exit, which avoided the problem. But
> 2a4d9408c9e8 removed pci_dev->driver (since it's redundant with
> device->driver), so we no longer take the early exit, which leads to havoc
> in ->runtime_resume().
>
> Similarly, we could call the driver's ->runtime_idle() method after its
> ->remove() method.
>
> Avoid the problem by dropping the pm_runtime_get_sync() and
> pm_runtime_put_sync() from local_pci_probe() and pci_device_remove(),
> respectively.
>
> Add pm_runtime_get_noresume(), which uses no driver PM callbacks, to the
> pci_pm_init() enumeration path. This will prevent PM-runtime from touching
> the device until it has a driver that supports PM-runtime.
>
> Link: https://lore.kernel.org/r/CAJZ5v0impb8uscbp8LUTBMExfMoGz=cPrTWhSGh0GF_SANNKPQ@mail.gmail.com
> Fixes: 2a4d9408c9e8 ("PCI: Use to_pci_driver() instead of pci_dev->driver")
> Reported-by: Robert Święcki <robert@...ecki.net>
> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 1d98c974381c..41cdf510214f 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -309,16 +309,6 @@ static long local_pci_probe(void *_ddi)
> struct device *dev = &pci_dev->dev;
> int rc;
>
> - /*
> - * Unbound PCI devices are always put in D0, regardless of
> - * runtime PM status. During probe, the device is set to
> - * active and the usage count is incremented. If the driver
> - * supports runtime PM, it should call pm_runtime_put_noidle(),
> - * or any other runtime PM helper function decrementing the usage
> - * count, in its probe routine and pm_runtime_get_noresume() in
> - * its remove routine.
> - */
> - pm_runtime_get_sync(dev);
> rc = pci_drv->probe(pci_dev, ddi->id);
> if (!rc)
> return rc;
> @@ -464,9 +454,6 @@ static void pci_device_remove(struct device *dev)
> pcibios_free_irq(pci_dev);
> pci_iov_remove(pci_dev);
>
> - /* Undo the runtime PM settings in local_pci_probe() */
> - pm_runtime_put_sync(dev);
> -
> /*
> * If the device is still on, set the power state as "unknown",
> * since it might change by the next time we load the driver.
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b88db815ee01..e9c38b994c73 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3097,7 +3097,15 @@ void pci_pm_init(struct pci_dev *dev)
> u16 pmc;
>
> pm_runtime_forbid(&dev->dev);
> +
> + /*
> + * Unbound PCI devices are always put in D0. If the driver supports
> + * runtime PM, it should call pm_runtime_put_noidle(), or any other
> + * runtime PM helper function decrementing the usage count, in its
> + * probe routine and pm_runtime_get_noresume() in its remove routine.
> + */
> pm_runtime_set_active(&dev->dev);
> + pm_runtime_get_noresume(&dev->dev);
> pm_runtime_enable(&dev->dev);
> device_enable_async_suspend(&dev->dev);
> dev->wakeup_prepared = false;
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