[PATCH V2] PM / core: fix deferred probe breaking suspend resume order

[Rafael J. Wysocki]

[+Greg]

On Thu, Mar 1, 2018 at 11:15 PM, Feng Kan <fkan at apm.com> wrote:
> When bridge and its endpoint is enumerated the devices are added to the
> dpm list. Afterward, the bridge defers probe when IOMMU is not ready.
> This causes the bridge to be moved to the end of the dpm list when
> deferred probe kicks in. The order of the dpm list for bridge and
> endpoint is reversed.
>
> Add reordering code to move the bridge and its children and consumers to
> the end of the pm list so the order for suspend and resume is not altered.
> The code also move device and its children and consumers to the tail of
> device_kset list if it is registered.

I assume that this has been tested and works as expected.

> Signed-off-by: Feng Kan <fkan at apm.com>
> Signed-off-by: Toan Le <toanle at apm.com>
> ---
>  V2:
>         1. change patch title from "move device and its children..."
>         2. move define based on Bjorn's comment
>         3. rename function name and comment content
>  drivers/base/base.h |  3 +++
>  drivers/base/core.c | 22 ++++++++++++++++++++++
>  drivers/base/dd.c   |  8 ++++----
>  3 files changed, 29 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index d800de6..a75c302 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -161,3 +161,6 @@ static inline void module_remove_driver(struct device_driver *drv) { }
>  extern void device_links_no_driver(struct device *dev);
>  extern bool device_links_busy(struct device *dev);
>  extern void device_links_unbind_consumers(struct device *dev);
> +
> +/* device pm support */
> +void device_pm_move_to_tail(struct device *dev);
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 110230d..0a0756b 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -148,6 +148,28 @@ static int device_reorder_to_tail(struct device *dev, void *not_used)
>  }
>
>  /**
> + * device_pm_move_to_tail - move device and its children and consumers to end of
> + *                          pm and device kset list

This has to be one line.  Maybe something like "Move set of devices to
the end of device lists" and then describe how it works below.

> + * @dev: current device pointer
> + *
> + * This is a lock held version of the device_reorder_to_tail.

I'd say "This is a device_reorder_to_tail() wrapper taking the
requisite locks." and put an empty comment line after that.

> +  Function checks

"It checks"

> + * if the device is registered and moves it to the end of device_kset list. Also
> + * if the device is pm initialized, move the device to the end of the pm list.
> + * Then the function iterate through the children and device link consumers to
> + * do the same for each found.

But generally I'd say "It moves the device along with all of its
children and all of its consumers to the ends of the device_kset and
dpm_list lists, recursively".

> + */
> +void device_pm_move_to_tail(struct device *dev)
> +{
> +       int idx;
> +
> +       idx = device_links_read_lock();
> +       device_pm_lock();
> +       device_reorder_to_tail(dev, NULL);
> +       device_pm_unlock();
> +       device_links_read_unlock(idx);
> +}
> +
> +/**
>   * device_link_add - Create a link between two devices.
>   * @consumer: Consumer end of the link.
>   * @supplier: Supplier end of the link.
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 2c964f5..7e9d1ef 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -121,11 +121,11 @@ static void deferred_probe_work_func(struct work_struct *work)
>                  * Force the device to the end of the dpm_list since
>                  * the PM code assumes that the order we add things to
>                  * the list is a good order for suspend but deferred
> -                * probe makes that very unsafe.
> +                * probe makes that very unsafe. Move any children and
> +                * consumers belong to the device to the end of the list.
> +                * This way the suspend resume order won't be corrupted.

Why do you need to change this comment?

>                  */
> -               device_pm_lock();
> -               device_pm_move_last(dev);
> -               device_pm_unlock();
> +               device_pm_move_to_tail(dev);
>
>                 dev_dbg(dev, "Retrying from deferred list\n");
>                 if (initcall_debug && !initcalls_done)
> --
> 1.8.3.1
>