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

[Bjorn Helgaas]

On Thu, Mar 01, 2018 at 02:15:14PM -0800, Feng Kan 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.

I'm not very familiar with PM, so can you connect some of the dots
here for me?

When you say "the bridge defers probe when IOMMU is not ready", are
you talking about pcie_portdrv_probe() claiming a PCIe port?

How does this connect with the IOMMU?  Where do we figure out that the
IOMMU is not ready?

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