From mboxrd@z Thu Jan 1 00:00:00 1970 From: Saravana Kannan Subject: [PATCH v9 1/7] driver core: Add support for linking devices during device addition Date: Wed, 31 Jul 2019 15:17:14 -0700 Message-ID: <20190731221721.187713-2-saravanak@google.com> References: <20190731221721.187713-1-saravanak@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <20190731221721.187713-1-saravanak@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Rob Herring , Mark Rutland , Greg Kroah-Hartman , "Rafael J. Wysocki" , Frank Rowand Cc: Saravana Kannan , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, David Collins , kernel-team@android.com List-Id: devicetree@vger.kernel.org When devices are added, the bus might want to create device links to track functional dependencies between supplier and consumer devices. This tracking of supplier-consumer relationship allows optimizing device probe order and tracking whether all consumers of a supplier are active. The add_links bus callback is added to support this. However, when consumer devices are added, they might not have a supplier device to link to despite needing mandatory resources/functionality from one or more suppliers. A waiting_for_suppliers list is created to track such consumers and retry linking them when new devices get added. Signed-off-by: Saravana Kannan --- drivers/base/core.c | 83 ++++++++++++++++++++++++++++++++++++++++++ include/linux/device.h | 14 +++++++ 2 files changed, 97 insertions(+) diff --git a/drivers/base/core.c b/drivers/base/core.c index 950e3bd0f45c..62d416e667bd 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -44,6 +44,8 @@ early_param("sysfs.deprecated", sysfs_deprecated_setup); #endif /* Device links support. */ +static LIST_HEAD(wait_for_suppliers); +static DEFINE_MUTEX(wfs_lock); #ifdef CONFIG_SRCU static DEFINE_MUTEX(device_links_lock); @@ -416,6 +418,51 @@ struct device_link *device_link_add(struct device *consumer, } EXPORT_SYMBOL_GPL(device_link_add); +/** + * device_link_wait_for_supplier - Mark device as waiting for supplier + * @consumer: Consumer device + * + * Marks the consumer device as waiting for suppliers to become available. The + * consumer device will never be probed until it's unmarked as waiting for + * suppliers. The caller is responsible for adding the link to the supplier + * once the supplier device is present. + * + * This function is NOT meant to be called from the probe function of the + * consumer but rather from code that creates/adds the consumer device. + */ +static void device_link_wait_for_supplier(struct device *consumer) +{ + mutex_lock(&wfs_lock); + list_add_tail(&consumer->links.needs_suppliers, &wait_for_suppliers); + mutex_unlock(&wfs_lock); +} + +/** + * device_link_check_waiting_consumers - Try to unmark waiting consumers + * + * Loops through all consumers waiting on suppliers and tries to add all their + * supplier links. If that succeeds, the consumer device is unmarked as waiting + * for suppliers. Otherwise, they are left marked as waiting on suppliers, + * + * The add_links bus callback is expected to return 0 if it has found and added + * all the supplier links for the consumer device. It should return an error if + * it isn't able to do so. + * + * The caller of device_link_wait_for_supplier() is expected to call this once + * it's aware of potential suppliers becoming available. + */ +static void device_link_check_waiting_consumers(void) +{ + struct device *dev, *tmp; + + mutex_lock(&wfs_lock); + list_for_each_entry_safe(dev, tmp, &wait_for_suppliers, + links.needs_suppliers) + if (!dev->bus->add_links(dev)) + list_del_init(&dev->links.needs_suppliers); + mutex_unlock(&wfs_lock); +} + static void device_link_free(struct device_link *link) { while (refcount_dec_not_one(&link->rpm_active)) @@ -550,6 +597,19 @@ int device_links_check_suppliers(struct device *dev) struct device_link *link; int ret = 0; + /* + * If a device is waiting for one or more suppliers (in + * wait_for_suppliers list), it is not ready to probe yet. So just + * return -EPROBE_DEFER without having to check the links with existing + * suppliers. + */ + mutex_lock(&wfs_lock); + if (!list_empty(&dev->links.needs_suppliers)) { + mutex_unlock(&wfs_lock); + return -EPROBE_DEFER; + } + mutex_unlock(&wfs_lock); + device_links_write_lock(); list_for_each_entry(link, &dev->links.suppliers, c_node) { @@ -834,6 +894,10 @@ static void device_links_purge(struct device *dev) { struct device_link *link, *ln; + mutex_lock(&wfs_lock); + list_del(&dev->links.needs_suppliers); + mutex_unlock(&wfs_lock); + /* * Delete all of the remaining links from this device to any other * devices (either consumers or suppliers). @@ -1698,6 +1762,7 @@ void device_initialize(struct device *dev) #endif INIT_LIST_HEAD(&dev->links.consumers); INIT_LIST_HEAD(&dev->links.suppliers); + INIT_LIST_HEAD(&dev->links.needs_suppliers); dev->links.status = DL_DEV_NO_DRIVER; } EXPORT_SYMBOL_GPL(device_initialize); @@ -2133,6 +2198,24 @@ int device_add(struct device *dev) BUS_NOTIFY_ADD_DEVICE, dev); kobject_uevent(&dev->kobj, KOBJ_ADD); + + /* + * Check if any of the other devices (consumers) have been waiting for + * this device (supplier) to be added so that they can create a device + * link to it. + * + * This needs to happen after device_pm_add() because device_link_add() + * requires the supplier be registered before it's called. + * + * But this also needs to happe before bus_probe_device() to make sure + * waiting consumers can link to it before the driver is bound to the + * device and the driver sync_state callback is called for this device. + */ + device_link_check_waiting_consumers(); + + if (dev->bus && dev->bus->add_links && dev->bus->add_links(dev)) + device_link_wait_for_supplier(dev); + bus_probe_device(dev); if (parent) klist_add_tail(&dev->p->knode_parent, diff --git a/include/linux/device.h b/include/linux/device.h index 5093691f56e7..dbcf1de5e9fa 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -78,6 +78,17 @@ extern void bus_remove_file(struct bus_type *, struct bus_attribute *); * -EPROBE_DEFER it will queue the device for deferred probing. * @uevent: Called when a device is added, removed, or a few other things * that generate uevents to add the environment variables. + * @add_links: Called, perhaps multiple times per device, after a device is + * added to this bus. The function is expected to create device + * links to all the suppliers of the input device that are + * available at the time this function is called. As in, the + * function should NOT stop at the first failed device link if + * other unlinked supplier devices are present in the system. + * + * Return 0 if device links have been successfully created to all + * the suppliers of this device. Return an error if some of the + * suppliers are not yet available and this function needs to be + * reattempted in the future. * @probe: Called when a new device or driver add to this bus, and callback * the specific driver's probe to initial the matched device. * @remove: Called when a device removed from this bus. @@ -122,6 +133,7 @@ struct bus_type { int (*match)(struct device *dev, struct device_driver *drv); int (*uevent)(struct device *dev, struct kobj_uevent_env *env); + int (*add_links)(struct device *dev); int (*probe)(struct device *dev); int (*remove)(struct device *dev); void (*shutdown)(struct device *dev); @@ -895,11 +907,13 @@ enum dl_dev_state { * struct dev_links_info - Device data related to device links. * @suppliers: List of links to supplier devices. * @consumers: List of links to consumer devices. + * @needs_suppliers: Hook to global list of devices waiting for suppliers. * @status: Driver status information. */ struct dev_links_info { struct list_head suppliers; struct list_head consumers; + struct list_head needs_suppliers; enum dl_dev_state status; }; -- 2.22.0.709.g102302147b-goog