Re: [PATCH net v2 1/1] net: phy: Don't trigger state machine while in suspend

[Rafael J. Wysocki]

On Wed, Jun 8, 2022 at 11:57 AM Lukas Wunner <lukas@xxxxxxxxx> wrote:
>
> Upon system sleep, mdio_bus_phy_suspend() stops the phy_state_machine(),
> but subsequent interrupts may retrigger it:
>
> They may have been left enabled to facilitate wakeup and are not
> quiesced until the ->suspend_noirq() phase.  Unwanted interrupts may
> hence occur between mdio_bus_phy_suspend() and dpm_suspend_noirq(),
> as well as between dpm_resume_noirq() and mdio_bus_phy_resume().
>
> Retriggering the phy_state_machine() through an interrupt is not only
> undesirable for the reason given in mdio_bus_phy_suspend() (freezing it
> midway with phydev->lock held), but also because the PHY may be
> inaccessible after it's suspended:  Accesses to USB-attached PHYs are
> blocked once usb_suspend_both() clears the can_submit flag and PHYs on
> PCI network cards may become inaccessible upon suspend as well.
>
> Amend phy_interrupt() to avoid triggering the state machine if the PHY
> is suspended.  Signal wakeup instead if the attached net_device or its
> parent has been configured as a wakeup source.  (Those conditions are
> identical to mdio_bus_phy_may_suspend().)  Postpone handling of the
> interrupt until the PHY has resumed.
>
> Before stopping the phy_state_machine() in mdio_bus_phy_suspend(),
> wait for a concurrent phy_interrupt() to run to completion.  That is
> necessary because phy_interrupt() may have checked the PHY's suspend
> status before the system sleep transition commenced and it may thus
> retrigger the state machine after it was stopped.
>
> Likewise, after re-enabling interrupt handling in mdio_bus_phy_resume(),
> wait for a concurrent phy_interrupt() to complete to ensure that
> interrupts which it postponed are properly rerun.
>
> Link: https://lore.kernel.org/netdev/a5315a8a-32c2-962f-f696-de9a26d30091@xxxxxxxxxxx/
> Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>

Looks reasonable to me.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

> ---
>  drivers/net/phy/phy.c        | 23 +++++++++++++++++++++++
>  drivers/net/phy/phy_device.c | 23 +++++++++++++++++++++++
>  include/linux/phy.h          |  6 ++++++
>  3 files changed, 52 insertions(+)
>
> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
> index ef62f357b76d..8d3ee3a6495b 100644
> --- a/drivers/net/phy/phy.c
> +++ b/drivers/net/phy/phy.c
> @@ -31,6 +31,7 @@
>  #include <linux/io.h>
>  #include <linux/uaccess.h>
>  #include <linux/atomic.h>
> +#include <linux/suspend.h>
>  #include <net/netlink.h>
>  #include <net/genetlink.h>
>  #include <net/sock.h>
> @@ -976,6 +977,28 @@ static irqreturn_t phy_interrupt(int irq, void *phy_dat)
>         struct phy_driver *drv = phydev->drv;
>         irqreturn_t ret;
>
> +       /* Wakeup interrupts may occur during a system sleep transition.
> +        * Postpone handling until the PHY has resumed.
> +        */
> +       if (IS_ENABLED(CONFIG_PM_SLEEP) && phydev->irq_suspended) {
> +               struct net_device *netdev = phydev->attached_dev;
> +
> +               if (netdev) {
> +                       struct device *parent = netdev->dev.parent;
> +
> +                       if (netdev->wol_enabled)
> +                               pm_system_wakeup();
> +                       else if (device_may_wakeup(&netdev->dev))
> +                               pm_wakeup_dev_event(&netdev->dev, 0, true);
> +                       else if (parent && device_may_wakeup(parent))
> +                               pm_wakeup_dev_event(parent, 0, true);
> +               }
> +
> +               phydev->irq_rerun = 1;
> +               disable_irq_nosync(irq);
> +               return IRQ_HANDLED;
> +       }
> +
>         mutex_lock(&phydev->lock);
>         ret = drv->handle_interrupt(phydev);
>         mutex_unlock(&phydev->lock);
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 431a8719c635..46acddd865a7 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -278,6 +278,15 @@ static __maybe_unused int mdio_bus_phy_suspend(struct device *dev)
>         if (phydev->mac_managed_pm)
>                 return 0;
>
> +       /* Wakeup interrupts may occur during the system sleep transition when
> +        * the PHY is inaccessible. Set flag to postpone handling until the PHY
> +        * has resumed. Wait for concurrent interrupt handler to complete.
> +        */
> +       if (phy_interrupt_is_valid(phydev)) {
> +               phydev->irq_suspended = 1;
> +               synchronize_irq(phydev->irq);
> +       }
> +
>         /* We must stop the state machine manually, otherwise it stops out of
>          * control, possibly with the phydev->lock held. Upon resume, netdev
>          * may call phy routines that try to grab the same lock, and that may
> @@ -315,6 +324,20 @@ static __maybe_unused int mdio_bus_phy_resume(struct device *dev)
>         if (ret < 0)
>                 return ret;
>  no_resume:
> +       if (phy_interrupt_is_valid(phydev)) {
> +               phydev->irq_suspended = 0;
> +               synchronize_irq(phydev->irq);
> +
> +               /* Rerun interrupts which were postponed by phy_interrupt()
> +                * because they occurred during the system sleep transition.
> +                */
> +               if (phydev->irq_rerun) {
> +                       phydev->irq_rerun = 0;
> +                       enable_irq(phydev->irq);
> +                       irq_wake_thread(phydev->irq, phydev);
> +               }
> +       }
> +
>         if (phydev->attached_dev && phydev->adjust_link)
>                 phy_start_machine(phydev);
>
> diff --git a/include/linux/phy.h b/include/linux/phy.h
> index 508f1149665b..b09f7d36cff2 100644
> --- a/include/linux/phy.h
> +++ b/include/linux/phy.h
> @@ -572,6 +572,10 @@ struct macsec_ops;
>   * @mdix_ctrl: User setting of crossover
>   * @pma_extable: Cached value of PMA/PMD Extended Abilities Register
>   * @interrupts: Flag interrupts have been enabled
> + * @irq_suspended: Flag indicating PHY is suspended and therefore interrupt
> + *                 handling shall be postponed until PHY has resumed
> + * @irq_rerun: Flag indicating interrupts occurred while PHY was suspended,
> + *             requiring a rerun of the interrupt handler after resume
>   * @interface: enum phy_interface_t value
>   * @skb: Netlink message for cable diagnostics
>   * @nest: Netlink nest used for cable diagnostics
> @@ -626,6 +630,8 @@ struct phy_device {
>
>         /* Interrupts are enabled */
>         unsigned interrupts:1;
> +       unsigned irq_suspended:1;
> +       unsigned irq_rerun:1;
>
>         enum phy_state state;
>
> --
> 2.35.2
>