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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Dmitry Osipenko <digetx@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Saravana Kannan <saravanak@google.com>,
        Lukas Wunner <lukas@wunner.de>,
        Jon Hunter <jonathanh@nvidia.com>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>
Subject: Re: [PATCH v2] driver core: Remove device link creation limitation
Date:   Mon, 29 Jul 2019 23:50:05 +0200
Message-ID: <7944678.tFQQHhpDPp@kreacher>
In-Reply-To: <c8960d91-4446-9acf-5575-e442a652bd05@gmail.com>
References: <2305283.AStDPdUUnE@kreacher> <c8960d91-4446-9acf-5575-e442a652bd05@gmail.com>
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On Monday, July 29, 2019 5:48:57 PM CEST Dmitry Osipenko wrote:
> 16.07.2019 18:21, Rafael J. Wysocki пишет:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Subject: [PATCH] driver core: Remove device link creation limitation
> > 
> > If device_link_add() is called for a consumer/supplier pair with an
> > existing device link between them and the existing link's type is
> > not in agreement with the flags passed to that function by its
> > caller, NULL will be returned.  That is seriously inconvenient,
> > because it forces the callers of device_link_add() to worry about
> > what others may or may not do even if that is not relevant to them
> > for any other reasons.
> > 
> > It turns out, however, that this limitation can be made go away
> > relatively easily.
> > 
> > The underlying observation is that if DL_FLAG_STATELESS has been
> > passed to device_link_add() in flags for the given consumer/supplier
> > pair at least once, calling either device_link_del() or
> > device_link_remove() to release the link returned by it should work,
> > but there are no other requirements associated with that flag.  In
> > turn, if at least one of the callers of device_link_add() for the
> > given consumer/supplier pair has not passed DL_FLAG_STATELESS to it
> > in flags, the driver core should track the status of the link and act
> > on it as appropriate (ie. the link should be treated as "managed").
> > This means that DL_FLAG_STATELESS needs to be set for managed device
> > links and it should be valid to call device_link_del() or
> > device_link_remove() to drop references to them in certain
> > sutiations.
> > 
> > To allow that to happen, introduce a new (internal) device link flag
> > called DL_FLAG_MANAGED and make device_link_add() set it automatically
> > whenever DL_FLAG_STATELESS is not passed to it.  Also make it take
> > additional references to existing device links that were previously
> > stateless (that is, with DL_FLAG_STATELESS set and DL_FLAG_MANAGED
> > unset) and will need to be managed going forward and initialize
> > their status (which has been DL_STATE_NONE so far).
> > 
> > Accordingly, when a managed device link is dropped automatically
> > by the driver core, make it clear DL_FLAG_MANAGED, reset the link's
> > status back to DL_STATE_NONE and drop the reference to it associated
> > with DL_FLAG_MANAGED instead of just deleting it right away (to
> > allow it to stay around in case it still needs to be released
> > explicitly by someone).
> > 
> > With that, since setting DL_FLAG_STATELESS doesn't mean that the
> > device link in question is not managed any more, replace all of the
> > status-tracking checks against DL_FLAG_STATELESS with analogous
> > checks against DL_FLAG_MANAGED and update the documentation to
> > reflect these changes.
> > 
> > While at it, make device_link_add() reject flags that it does not
> > recognize, including DL_FLAG_MANAGED.
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Reviewed-by: Saravana Kannan <saravanak@google.com>
> > Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> > ---
> > 
> > -> v2:
> >    * Add a check to device_link_add() to return NULL if unrecognized flags are
> >      passed to it.
> >    * Modify kerneldoc comments around DL_FLAG_MANAGED.
> > 
> > I've tentatively added the Tested-by tag from Marek, because I don't expect
> > the changes made between the initial posting and the v2 to make any difference
> > for him.
> > 
> > ---
> >  Documentation/driver-api/device_link.rst |    4 
> >  drivers/base/core.c                      |  176 +++++++++++++++++--------------
> >  drivers/base/power/runtime.c             |    4 
> >  include/linux/device.h                   |    4 
> >  4 files changed, 106 insertions(+), 82 deletions(-)
> > 
> > Index: linux-pm/drivers/base/core.c
> > ===================================================================
> > --- linux-pm.orig/drivers/base/core.c
> > +++ linux-pm/drivers/base/core.c
> > @@ -124,6 +124,50 @@ static int device_is_dependent(struct de
> >  	return ret;
> >  }
> >  
> > +static void device_link_init_status(struct device_link *link,
> > +				    struct device *consumer,
> > +				    struct device *supplier)
> > +{
> > +	switch (supplier->links.status) {
> > +	case DL_DEV_PROBING:
> > +		switch (consumer->links.status) {
> > +		case DL_DEV_PROBING:
> > +			/*
> > +			 * A consumer driver can create a link to a supplier
> > +			 * that has not completed its probing yet as long as it
> > +			 * knows that the supplier is already functional (for
> > +			 * example, it has just acquired some resources from the
> > +			 * supplier).
> > +			 */
> > +			link->status = DL_STATE_CONSUMER_PROBE;
> > +			break;
> > +		default:
> > +			link->status = DL_STATE_DORMANT;
> > +			break;
> > +		}
> > +		break;
> > +	case DL_DEV_DRIVER_BOUND:
> > +		switch (consumer->links.status) {
> > +		case DL_DEV_PROBING:
> > +			link->status = DL_STATE_CONSUMER_PROBE;
> > +			break;
> > +		case DL_DEV_DRIVER_BOUND:
> > +			link->status = DL_STATE_ACTIVE;
> > +			break;
> > +		default:
> > +			link->status = DL_STATE_AVAILABLE;
> > +			break;
> > +		}
> > +		break;
> > +	case DL_DEV_UNBINDING:
> > +		link->status = DL_STATE_SUPPLIER_UNBIND;
> > +		break;
> > +	default:
> > +		link->status = DL_STATE_DORMANT;
> > +		break;
> > +	}
> > +}
> > +
> >  static int device_reorder_to_tail(struct device *dev, void *not_used)
> >  {
> >  	struct device_link *link;
> > @@ -165,6 +209,10 @@ void device_pm_move_to_tail(struct devic
> >  	device_links_read_unlock(idx);
> >  }
> >  
> > +#define DL_MANAGED_LINK_FLAGS (DL_FLAG_AUTOREMOVE_CONSUMER | \
> > +			       DL_FLAG_AUTOREMOVE_SUPPLIER | \
> > +			       DL_FLAG_AUTOPROBE_CONSUMER)
> > +
> >  /**
> >   * device_link_add - Create a link between two devices.
> >   * @consumer: Consumer end of the link.
> > @@ -179,9 +227,9 @@ void device_pm_move_to_tail(struct devic
> >   * of the link.  If DL_FLAG_PM_RUNTIME is not set, DL_FLAG_RPM_ACTIVE will be
> >   * ignored.
> >   *
> > - * If DL_FLAG_STATELESS is set in @flags, the link is not going to be managed by
> > - * the driver core and, in particular, the caller of this function is expected
> > - * to drop the reference to the link acquired by it directly.
> > + * If DL_FLAG_STATELESS is set in @flags, the caller of this function is
> > + * expected to release the link returned by it directly with the help of either
> > + * device_link_del() or device_link_remove().
> >   *
> >   * If that flag is not set, however, the caller of this function is handing the
> >   * management of the link over to the driver core entirely and its return value
> > @@ -201,9 +249,16 @@ void device_pm_move_to_tail(struct devic
> >   * be used to request the driver core to automaticall probe for a consmer
> >   * driver after successfully binding a driver to the supplier device.
> >   *
> > - * The combination of DL_FLAG_STATELESS and either DL_FLAG_AUTOREMOVE_CONSUMER
> > - * or DL_FLAG_AUTOREMOVE_SUPPLIER set in @flags at the same time is invalid and
> > - * will cause NULL to be returned upfront.
> > + * The combination of DL_FLAG_STATELESS and one of DL_FLAG_AUTOREMOVE_CONSUMER,
> > + * DL_FLAG_AUTOREMOVE_SUPPLIER, or DL_FLAG_AUTOPROBE_CONSUMER set in @flags at
> > + * the same time is invalid and will cause NULL to be returned upfront.
> > + * However, if a device link between the given @consumer and @supplier pair
> > + * exists already when this function is called for them, the existing link will
> > + * be returned regardless of its current type and status (the link's flags may
> > + * be modified then).  The caller of this function is then expected to treat
> > + * the link as though it has just been created, so (in particular) if
> > + * DL_FLAG_STATELESS was passed in @flags, the link needs to be released
> > + * explicitly when not needed any more (as stated above).
> >   *
> >   * A side effect of the link creation is re-ordering of dpm_list and the
> >   * devices_kset list by moving the consumer device and all devices depending
> > @@ -220,10 +275,8 @@ struct device_link *device_link_add(stru
> >  	struct device_link *link;
> >  
> >  	if (!consumer || !supplier ||
> > -	    (flags & DL_FLAG_STATELESS &&
> > -	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER |
> > -		      DL_FLAG_AUTOREMOVE_SUPPLIER |
> > -		      DL_FLAG_AUTOPROBE_CONSUMER)) ||
> > +	    (flags & ~(DL_FLAG_STATELESS | DL_MANAGED_LINK_FLAGS)) ||
> > +	    (flags & DL_FLAG_STATELESS && flags & DL_MANAGED_LINK_FLAGS) ||
> >  	    (flags & DL_FLAG_AUTOPROBE_CONSUMER &&
> >  	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER |
> >  		      DL_FLAG_AUTOREMOVE_SUPPLIER)))
> > @@ -236,6 +289,9 @@ struct device_link *device_link_add(stru
> >  		}
> >  	}
> >  
> > +	if (!(flags & DL_FLAG_STATELESS))
> > +		flags |= DL_FLAG_MANAGED;
> > +
> >  	device_links_write_lock();
> >  	device_pm_lock();
> >  
> > @@ -262,15 +318,6 @@ struct device_link *device_link_add(stru
> >  		if (link->consumer != consumer)
> >  			continue;
> >  
> > -		/*
> > -		 * Don't return a stateless link if the caller wants a stateful
> > -		 * one and vice versa.
> > -		 */
> > -		if (WARN_ON((flags & DL_FLAG_STATELESS) != (link->flags & DL_FLAG_STATELESS))) {
> > -			link = NULL;
> > -			goto out;
> > -		}
> > -
> >  		if (flags & DL_FLAG_PM_RUNTIME) {
> >  			if (!(link->flags & DL_FLAG_PM_RUNTIME)) {
> >  				pm_runtime_new_link(consumer);
> > @@ -281,6 +328,7 @@ struct device_link *device_link_add(stru
> >  		}
> >  
> >  		if (flags & DL_FLAG_STATELESS) {
> > +			link->flags |= DL_FLAG_STATELESS;
> >  			kref_get(&link->kref);
> >  			goto out;
> >  		}
> > @@ -299,6 +347,11 @@ struct device_link *device_link_add(stru
> >  			link->flags &= ~(DL_FLAG_AUTOREMOVE_CONSUMER |
> >  					 DL_FLAG_AUTOREMOVE_SUPPLIER);
> >  		}
> > +		if (!(link->flags & DL_FLAG_MANAGED)) {
> > +			kref_get(&link->kref);
> > +			link->flags |= DL_FLAG_MANAGED;
> > +			device_link_init_status(link, consumer, supplier);
> > +		}
> >  		goto out;
> >  	}
> >  
> > @@ -325,48 +378,10 @@ struct device_link *device_link_add(stru
> >  	kref_init(&link->kref);
> >  
> >  	/* Determine the initial link state. */
> > -	if (flags & DL_FLAG_STATELESS) {
> > +	if (flags & DL_FLAG_STATELESS)
> >  		link->status = DL_STATE_NONE;
> > -	} else {
> > -		switch (supplier->links.status) {
> > -		case DL_DEV_PROBING:
> > -			switch (consumer->links.status) {
> > -			case DL_DEV_PROBING:
> > -				/*
> > -				 * A consumer driver can create a link to a
> > -				 * supplier that has not completed its probing
> > -				 * yet as long as it knows that the supplier is
> > -				 * already functional (for example, it has just
> > -				 * acquired some resources from the supplier).
> > -				 */
> > -				link->status = DL_STATE_CONSUMER_PROBE;
> > -				break;
> > -			default:
> > -				link->status = DL_STATE_DORMANT;
> > -				break;
> > -			}
> > -			break;
> > -		case DL_DEV_DRIVER_BOUND:
> > -			switch (consumer->links.status) {
> > -			case DL_DEV_PROBING:
> > -				link->status = DL_STATE_CONSUMER_PROBE;
> > -				break;
> > -			case DL_DEV_DRIVER_BOUND:
> > -				link->status = DL_STATE_ACTIVE;
> > -				break;
> > -			default:
> > -				link->status = DL_STATE_AVAILABLE;
> > -				break;
> > -			}
> > -			break;
> > -		case DL_DEV_UNBINDING:
> > -			link->status = DL_STATE_SUPPLIER_UNBIND;
> > -			break;
> > -		default:
> > -			link->status = DL_STATE_DORMANT;
> > -			break;
> > -		}
> > -	}
> > +	else
> > +		device_link_init_status(link, consumer, supplier);
> >  
> >  	/*
> >  	 * Some callers expect the link creation during consumer driver probe to
> > @@ -528,7 +543,7 @@ static void device_links_missing_supplie
> >   * mark the link as "consumer probe in progress" to make the supplier removal
> >   * wait for us to complete (or bad things may happen).
> >   *
> > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> >   */
> >  int device_links_check_suppliers(struct device *dev)
> >  {
> > @@ -538,7 +553,7 @@ int device_links_check_suppliers(struct
> >  	device_links_write_lock();
> >  
> >  	list_for_each_entry(link, &dev->links.suppliers, c_node) {
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		if (link->status != DL_STATE_AVAILABLE) {
> > @@ -563,7 +578,7 @@ int device_links_check_suppliers(struct
> >   *
> >   * Also change the status of @dev's links to suppliers to "active".
> >   *
> > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> >   */
> >  void device_links_driver_bound(struct device *dev)
> >  {
> > @@ -572,7 +587,7 @@ void device_links_driver_bound(struct de
> >  	device_links_write_lock();
> >  
> >  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		/*
> > @@ -593,7 +608,7 @@ void device_links_driver_bound(struct de
> >  	}
> >  
> >  	list_for_each_entry(link, &dev->links.suppliers, c_node) {
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		WARN_ON(link->status != DL_STATE_CONSUMER_PROBE);
> > @@ -605,6 +620,13 @@ void device_links_driver_bound(struct de
> >  	device_links_write_unlock();
> >  }
> >  
> > +static void device_link_drop_managed(struct device_link *link)
> > +{
> > +	link->flags &= ~DL_FLAG_MANAGED;
> > +	WRITE_ONCE(link->status, DL_STATE_NONE);
> > +	kref_put(&link->kref, __device_link_del);
> > +}
> > +
> >  /**
> >   * __device_links_no_driver - Update links of a device without a driver.
> >   * @dev: Device without a drvier.
> > @@ -615,18 +637,18 @@ void device_links_driver_bound(struct de
> >   * unless they already are in the "supplier unbind in progress" state in which
> >   * case they need not be updated.
> >   *
> > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> >   */
> >  static void __device_links_no_driver(struct device *dev)
> >  {
> >  	struct device_link *link, *ln;
> >  
> >  	list_for_each_entry_safe_reverse(link, ln, &dev->links.suppliers, c_node) {
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER)
> > -			__device_link_del(&link->kref);
> > +			device_link_drop_managed(link);
> >  		else if (link->status == DL_STATE_CONSUMER_PROBE ||
> >  			 link->status == DL_STATE_ACTIVE)
> >  			WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
> > @@ -643,7 +665,7 @@ static void __device_links_no_driver(str
> >   * %__device_links_no_driver() to update links to suppliers for it as
> >   * appropriate.
> >   *
> > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> >   */
> >  void device_links_no_driver(struct device *dev)
> >  {
> > @@ -652,7 +674,7 @@ void device_links_no_driver(struct devic
> >  	device_links_write_lock();
> >  
> >  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		/*
> > @@ -680,7 +702,7 @@ void device_links_no_driver(struct devic
> >   * invoke %__device_links_no_driver() to update links to suppliers for it as
> >   * appropriate.
> >   *
> > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> >   */
> >  void device_links_driver_cleanup(struct device *dev)
> >  {
> > @@ -689,7 +711,7 @@ void device_links_driver_cleanup(struct
> >  	device_links_write_lock();
> >  
> >  	list_for_each_entry_safe(link, ln, &dev->links.consumers, s_node) {
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		WARN_ON(link->flags & DL_FLAG_AUTOREMOVE_CONSUMER);
> > @@ -702,7 +724,7 @@ void device_links_driver_cleanup(struct
> >  		 */
> >  		if (link->status == DL_STATE_SUPPLIER_UNBIND &&
> >  		    link->flags & DL_FLAG_AUTOREMOVE_SUPPLIER)
> > -			__device_link_del(&link->kref);
> > +			device_link_drop_managed(link);
> >  
> >  		WRITE_ONCE(link->status, DL_STATE_DORMANT);
> >  	}
> > @@ -724,7 +746,7 @@ void device_links_driver_cleanup(struct
> >   *
> >   * Return 'false' if there are no probing or active consumers.
> >   *
> > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> >   */
> >  bool device_links_busy(struct device *dev)
> >  {
> > @@ -734,7 +756,7 @@ bool device_links_busy(struct device *de
> >  	device_links_write_lock();
> >  
> >  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		if (link->status == DL_STATE_CONSUMER_PROBE
> > @@ -764,7 +786,7 @@ bool device_links_busy(struct device *de
> >   * driver to unbind and start over (the consumer will not re-probe as we have
> >   * changed the state of the link already).
> >   *
> > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> >   */
> >  void device_links_unbind_consumers(struct device *dev)
> >  {
> > @@ -776,7 +798,7 @@ void device_links_unbind_consumers(struc
> >  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> >  		enum device_link_state status;
> >  
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		status = link->status;
> > Index: linux-pm/drivers/base/power/runtime.c
> > ===================================================================
> > --- linux-pm.orig/drivers/base/power/runtime.c
> > +++ linux-pm/drivers/base/power/runtime.c
> > @@ -1624,7 +1624,7 @@ void pm_runtime_remove(struct device *de
> >   * runtime PM references to the device, drop the usage counter of the device
> >   * (as many times as needed).
> >   *
> > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > + * Links with the DL_FLAG_MANAGED flag unset are ignored.
> >   *
> >   * Since the device is guaranteed to be runtime-active at the point this is
> >   * called, nothing else needs to be done here.
> > @@ -1641,7 +1641,7 @@ void pm_runtime_clean_up_links(struct de
> >  	idx = device_links_read_lock();
> >  
> >  	list_for_each_entry_rcu(link, &dev->links.consumers, s_node) {
> > -		if (link->flags & DL_FLAG_STATELESS)
> > +		if (!(link->flags & DL_FLAG_MANAGED))
> >  			continue;
> >  
> >  		while (refcount_dec_not_one(&link->rpm_active))
> > Index: linux-pm/include/linux/device.h
> > ===================================================================
> > --- linux-pm.orig/include/linux/device.h
> > +++ linux-pm/include/linux/device.h
> > @@ -829,12 +829,13 @@ enum device_link_state {
> >  /*
> >   * Device link flags.
> >   *
> > - * STATELESS: The core won't track the presence of supplier/consumer drivers.
> > + * STATELESS: The core will not remove this link automatically.
> >   * AUTOREMOVE_CONSUMER: Remove the link automatically on consumer driver unbind.
> >   * PM_RUNTIME: If set, the runtime PM framework will use this link.
> >   * RPM_ACTIVE: Run pm_runtime_get_sync() on the supplier during link creation.
> >   * AUTOREMOVE_SUPPLIER: Remove the link automatically on supplier driver unbind.
> >   * AUTOPROBE_CONSUMER: Probe consumer driver automatically after supplier binds.
> > + * MANAGED: The core tracks presence of supplier/consumer drivers (internal).
> >   */
> >  #define DL_FLAG_STATELESS		BIT(0)
> >  #define DL_FLAG_AUTOREMOVE_CONSUMER	BIT(1)
> > @@ -842,6 +843,7 @@ enum device_link_state {
> >  #define DL_FLAG_RPM_ACTIVE		BIT(3)
> >  #define DL_FLAG_AUTOREMOVE_SUPPLIER	BIT(4)
> >  #define DL_FLAG_AUTOPROBE_CONSUMER	BIT(5)
> > +#define DL_FLAG_MANAGED			BIT(6)
> >  
> >  /**
> >   * struct device_link - Device link representation.
> > Index: linux-pm/Documentation/driver-api/device_link.rst
> > ===================================================================
> > --- linux-pm.orig/Documentation/driver-api/device_link.rst
> > +++ linux-pm/Documentation/driver-api/device_link.rst
> > @@ -78,8 +78,8 @@ typically deleted in its ``->remove`` ca
> >  driver is compiled as a module, the device link is added on module load and
> >  orderly deleted on unload.  The same restrictions that apply to device link
> >  addition (e.g. exclusion of a parallel suspend/resume transition) apply equally
> > -to deletion.  Device links with ``DL_FLAG_STATELESS`` unset (i.e. managed
> > -device links) are deleted automatically by the driver core.
> > +to deletion.  Device links managed by the driver core are deleted automatically
> > +by it.
> >  
> >  Several flags may be specified on device link addition, two of which
> >  have already been mentioned above:  ``DL_FLAG_STATELESS`` to express that no
> > 
> > 
> > 
> > 
> 
> Hello Rafael,
> 
> This patch breaks NVIDIA Tegra DRM driver, which fails to probe now
> using the recent linux-next.
> 
> 	tegra-dc 54240000.dc: failed to link controllers
> 

Thanks for the report and sorry for the breakage!

My bad, obviously DL_FLAG_PM_RUNTIME must be accepted by device_link_add(),
as well as DL_FLAG_RPM_ACTIVE.

Please test the appended patch and let me know if it helps.

Greg, in case this is confirmed to fix the issue, do you want me to post it as a
separate patch, or would you prefer a v3 of the $subject one?

---
 drivers/base/core.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -213,6 +213,9 @@ void device_pm_move_to_tail(struct devic
 			       DL_FLAG_AUTOREMOVE_SUPPLIER | \
 			       DL_FLAG_AUTOPROBE_CONSUMER)
 
+#define DL_ADD_VALID_FLAGS (DL_MANAGED_LINK_FLAGS | DL_FLAG_STATELESS | \
+			    DL_FLAG_PM_RUNTIME | DL_FLAG_RPM_ACTIVE)
+
 /**
  * device_link_add - Create a link between two devices.
  * @consumer: Consumer end of the link.
@@ -274,8 +277,7 @@ struct device_link *device_link_add(stru
 {
 	struct device_link *link;
 
-	if (!consumer || !supplier ||
-	    (flags & ~(DL_FLAG_STATELESS | DL_MANAGED_LINK_FLAGS)) ||
+	if (!consumer || !supplier || flags & ~DL_ADD_VALID_FLAGS ||
 	    (flags & DL_FLAG_STATELESS && flags & DL_MANAGED_LINK_FLAGS) ||
 	    (flags & DL_FLAG_AUTOPROBE_CONSUMER &&
 	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER |