From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C4442C76190 for ; Tue, 23 Jul 2019 07:35:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8007E2251A for ; Tue, 23 Jul 2019 07:35:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563867319; bh=mhIeHLO8WJXu/5cpIFpoNcz7zEYLKGDHedpvOKMFGgs=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=LGVkGEXs1E9R3jCLaHIrywl/1r0255Xszjxm3qm90uinlAmOadYFUtfpeBymM/feM HDgcivqLjRswE8lLuDF538Zd9VVlZWb/QEq4kVvQ+v3SQgtWNV4ifk1OGZEyJQRrwE G7Ih7Lqy5eBzgbjuCYjQDh7R4vRMRk48YTk8tSLw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732757AbfGWHfK (ORCPT ); Tue, 23 Jul 2019 03:35:10 -0400 Received: from mail-oi1-f195.google.com ([209.85.167.195]:43934 "EHLO mail-oi1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729004AbfGWHfK (ORCPT ); Tue, 23 Jul 2019 03:35:10 -0400 Received: by mail-oi1-f195.google.com with SMTP id w79so31616092oif.10; Tue, 23 Jul 2019 00:35:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=jmyMItjW93T/+o6YoBNOCmTKsa0lLJteBNGbYjk+V7A=; b=KacyaOFnxO5/ejFcC1MdFF53GMtaPxesPXspIdnPKpjU2fNcOe0b0/NWegVs4NMou9 scwucO/yx9QFXSKW7OwE7vKkG4kGF0KcljlK/4UStHnDkdmz06iJdmLaMkaOnsAC/ddA V/CaNu162+6C3N4TKQVkN6EZVohBYRUhEIjMBMaPaUJdqGvxaVwAhV5aHojVjT9NIAAa lIbzV5FnybSw+eU4Uhfzn7WjBEysDUkVvaYcdVZM9I/ncsMTW9V5iqaGW5MNTJxKXscU 8WAlXYGhMgQ3T2qftMmY4+7tDpIJb9KCcL4FqEbJwziNaLuU9gsFHdmj3C44+XYERr5U Gh5w== X-Gm-Message-State: APjAAAULhcxZexpd3NWlQg0V6XcO40yKZIn8O6bk3jnxE/vbrJ16tljp rXGKt0VnTCHwUi0dZCeFjJQCPQGOTM/FO9GUDRE= X-Google-Smtp-Source: APXvYqy3GZwTCSVZ9IaOgopsiiks6HcQOEcr6pMmKLd9eqUEYuFqLMmPl56yGt7oe1pWZBahEx+TXPziIErRdXrAkNs= X-Received: by 2002:aca:edc8:: with SMTP id l191mr35898414oih.103.1563867307762; Tue, 23 Jul 2019 00:35:07 -0700 (PDT) MIME-Version: 1.0 References: <2305283.AStDPdUUnE@kreacher> In-Reply-To: <2305283.AStDPdUUnE@kreacher> From: "Rafael J. Wysocki" Date: Tue, 23 Jul 2019 09:34:54 +0200 Message-ID: Subject: Re: [PATCH v2] driver core: Remove device link creation limitation To: Greg Kroah-Hartman Cc: LKML , Linux PM , Saravana Kannan , Lukas Wunner , Jon Hunter , Ulf Hansson , Marek Szyprowski Content-Type: text/plain; charset="UTF-8" Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Hi Greg, On Tue, Jul 16, 2019 at 5:21 PM Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki > 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 > Reviewed-by: Saravana Kannan > Tested-by: Marek Szyprowski Do I need to resend this? I know that posting new things during a merge window is not most convenient, sorry about that. > --- > > -> 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 > > >