phy: use per-PHY lockdep keys

JIRA: https://issues.redhat.com/browse/RHEL-116007

commit cf02334
Author: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Date: Thu, 5 Jun 2025 14:25:49 +0300

  If the PHY driver uses another PHY internally (e.g. in case of eUSB2,
  repeaters are represented as PHYs), then it would trigger the following
  lockdep splat because all PHYs use a single static lockdep key and thus
  lockdep can not identify whether there is a dependency or not and
  reports a false positive.

  Make PHY subsystem use dynamic lockdep keys, assigning each driver a
  separate key. This way lockdep can correctly identify dependency graph
  between mutexes.

   ============================================
   WARNING: possible recursive locking detected
   6.15.0-rc7-next-20250522-12896-g3932f283970c #3455 Not tainted
   --------------------------------------------
   kworker/u51:0/78 is trying to acquire lock:
   ffff0008116554f0 (&phy->mutex){+.+.}-{4:4}, at: phy_init+0x4c/0x12c

   but task is already holding lock:
   ffff000813c10cf0 (&phy->mutex){+.+.}-{4:4}, at: phy_init+0x4c/0x12c

   other info that might help us debug this:
    Possible unsafe locking scenario:

          CPU0
          ----
     lock(&phy->mutex);
     lock(&phy->mutex);

    *** DEADLOCK ***

    May be due to missing lock nesting notation

   4 locks held by kworker/u51:0/78:
    #0: ffff000800010948 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x18c/0x5ec
    #1: ffff80008036bdb0 (deferred_probe_work){+.+.}-{0:0}, at: process_one_work+0x1b4/0x5ec
    #2: ffff0008094ac8f8 (&dev->mutex){....}-{4:4}, at: __device_attach+0x38/0x188
    #3: ffff000813c10cf0 (&phy->mutex){+.+.}-{4:4}, at: phy_init+0x4c/0x12c

   stack backtrace:
   CPU: 0 UID: 0 PID: 78 Comm: kworker/u51:0 Not tainted 6.15.0-rc7-next-20250522-12896-g3932f283970c #3455 PREEMPT
   Hardware name: Qualcomm CRD, BIOS 6.0.240904.BOOT.MXF.2.4-00528.1-HAMOA-1 09/ 4/2024
   Workqueue: events_unbound deferred_probe_work_func
   Call trace:
    show_stack+0x18/0x24 (C)
    dump_stack_lvl+0x90/0xd0
    dump_stack+0x18/0x24
    print_deadlock_bug+0x258/0x348
    __lock_acquire+0x10fc/0x1f84
    lock_acquire+0x1c8/0x338
    __mutex_lock+0xb8/0x59c
    mutex_lock_nested+0x24/0x30
    phy_init+0x4c/0x12c
    snps_eusb2_hsphy_init+0x54/0x1a0
    phy_init+0xe0/0x12c
    dwc3_core_init+0x450/0x10b4
    dwc3_core_probe+0xce4/0x15fc
    dwc3_probe+0x64/0xb0
    platform_probe+0x68/0xc4
    really_probe+0xbc/0x298
    __driver_probe_device+0x78/0x12c
    driver_probe_device+0x3c/0x160
    __device_attach_driver+0xb8/0x138
    bus_for_each_drv+0x84/0xe0
    __device_attach+0x9c/0x188
    device_initial_probe+0x14/0x20
    bus_probe_device+0xac/0xb0
    deferred_probe_work_func+0x8c/0xc8
    process_one_work+0x208/0x5ec
    worker_thread+0x1c0/0x368
    kthread+0x14c/0x20c
    ret_from_fork+0x10/0x20

  Fixes: 3584f63 ("phy: qcom: phy-qcom-snps-eusb2: Add support for eUSB2 repeater")
  Fixes: e246355 ("phy: amlogic: Add Amlogic AXG PCIE PHY Driver")
  Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
  Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
  Reported-by: Johan Hovold <johan+linaro@kernel.org>
  Link: https://lore.kernel.org/lkml/ZnpoAVGJMG4Zu-Jw@hovoldconsulting.com/
  Reviewed-by: Johan Hovold <johan+linaro@kernel.org>
  Tested-by: Johan Hovold <johan+linaro@kernel.org>
  Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
  Link: https://lore.kernel.org/r/20250605-phy-subinit-v3-1-1e1e849e10cd@oss.qualcomm.com
  Signed-off-by: Vinod Koul <vkoul@kernel.org>

Signed-off-by: Desnes Nunes <desnesn@redhat.com>

Author: Desnes Nunes

drivers/phy/phy-core.c

@@ -994,7 +994,8 @@ struct phy *phy_create(struct device *dev, struct device_node *node,
 	}
 
 	device_initialize(&phy->dev);
-	mutex_init(&phy->mutex);
+	lockdep_register_key(&phy->lockdep_key);
+	mutex_init_with_key(&phy->mutex, &phy->lockdep_key);
 
 	phy->dev.class = &phy_class;
 	phy->dev.parent = dev;
@@ -1259,6 +1260,8 @@ static void phy_release(struct device *dev)
 	dev_vdbg(dev, "releasing '%s'\n", dev_name(dev));
 	debugfs_remove_recursive(phy->debugfs);
 	regulator_put(phy->pwr);
+	mutex_destroy(&phy->mutex);
+	lockdep_unregister_key(&phy->lockdep_key);
 	ida_free(&phy_ida, phy->id);
 	kfree(phy);
 }

include/linux/phy/phy.h

@@ -149,6 +149,7 @@ struct phy_attrs {
  * @id: id of the phy device
  * @ops: function pointers for performing phy operations
  * @mutex: mutex to protect phy_ops
+ * @lockdep_key: lockdep information for this mutex
  * @init_count: used to protect when the PHY is used by multiple consumers
  * @power_count: used to protect when the PHY is used by multiple consumers
  * @attrs: used to specify PHY specific attributes
@@ -160,6 +161,7 @@ struct phy {
 	int			id;
 	const struct phy_ops	*ops;
 	struct mutex		mutex;
+	struct lock_class_key	lockdep_key;
 	int			init_count;
 	int			power_count;
 	struct phy_attrs	attrs;