On 29/07/2019 22:50, Rafael J. Wysocki wrote:
> 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@xxxxxxxxx>
>>> 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@xxxxxxxxx>
>>> Reviewed-by: Saravana Kannan <saravanak@xxxxxxxxxx>
>>> Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
>>> ---
>>>
>>> -> 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.
This also fixes a boot regression I have observed on Tegra210. So ...
Tested-by: Jon Hunter <jonathanh@xxxxxxxxxx>
Cheers
Jon
--
nvpublic
