Re: [PATCH 1/7] slimbus: qcom-ngd-ctrl: Fix up platform_driver registration

[Tj <tj.iam.tj@proton.me>]

Following up on the registration problems on recommendation of Konrad 
Dybcio.

I previously reported a hang during driver registration due to lock 
contention. Konrad pointed me to this thread. Earlier, I had fixed the 
issue myself and whilst doing it saw that order of registration is 
important - ctrl must be last otherwise it causes:

qcom,slim-ngd-ctrl 171c0000.slim-ngd: Failed to create device link 
(0x180) with supplier 34000000.pinctrl for 
/soc@0/slim-ngd@171c0000/slim@1/codec@1,0

so I'd be surprised if Patch 1 works (not had chance to test the patch 
series as yet).

With my local patch the result is:

qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM SAT: Rcvd master capability
qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM controller Registered

---
     slimbus: ngd: fix lock hang on probe

     Module contains two platform_drivers. The initial probe calls
     platform_register_driver() with the second struct platform_driver.

     This caused a hung task due to mutex lock in __driver_attach():

     INFO: task swapper/0:1 blocked for more than 1232 seconds.
                Not tainted 7.0.0.-rc2-sdm845 #89
     task:swapper/0    state:D pid:1 tgid:1 ppid:0 task_flags:0x0140 
flags:0x00000010
     Call trace:
     __switch_to_0x104/0x1c8 (T)
     __schedule+0x438/0x1168
     schedule+0x3c/0x120
     schedule_preempt_disabled+0x2c/0x50
     __mutex_lock.constprop.0+0x3d0/0x938
     __mutex_lock_slowpath+0x1c/0x30
     __driver_attach+0x38/0x280
     bus_for_each_dev+0x80/0xc8
     driver_attach+0x2c/0x40
     bus_add_driver+0x128/0x258
     driver_register+0x68/0x138
     __platform_driver_register+0x2c/0x40
     qcom_slim_ngd_ctrl_probe+0x1f4/0x400
     platform_probe+0x64/0xa8
     really_probe+0xc8/0x3f0
     __driver_probe_device+0x88/0x190
     driver_probe_device+0x44/0x120
     __driver_attach+0x138/0x280
     bus_for_each_dev+0x80/0xc8
     driver_attach+0x2c/0x40
     bus_add_driver+0x128/0x258
     driver_register+0x68/0x138
     __platform_driver_register+0x2c/0x40
     qcom_slim_ngd_ctrl_driver_init+0x24/0x38
     do_one_initcall+0x60/0x450
     kernel_init_freeable+0x23c/0x630
     kernel_init+0x2c/0x1f8
     ret_from_fork+0x10/0x20
     INFO: task swapper/0:1 is blocked on a mutex likely owned by task
     swapper/0:1.

     Showing all locks held in the system:
     2 locks held by swapper/0/1:
      #0: ffff000080ff80f8 (&dev->mutex){....}-{4:4}, at:
          __driver_attach+0x19c/0x2c0
      #1: ffff000080ff80f8 (&dev->mutex){....}-{4:4}, at:
          __driver_attach+0x38/0x2c0
     1 lock held by khungtaskd/73:
      #0: ffffbc5dfc38f1d8 (rcu_read_lock){....}-{1:3}, at:
          debug_show_all_locks+0x18/0x1f0

     After this fix:

     qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM SAT: Rcvd master capability
     qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM controller Registered

diff --git a/drivers/slimbus/qcom-ngd-ctrl.c 
b/drivers/slimbus/qcom-ngd-ctrl.c
index 9aa7218b4e8d2..abdd4ad57f2d2 100644
--- a/drivers/slimbus/qcom-ngd-ctrl.c
+++ b/drivers/slimbus/qcom-ngd-ctrl.c
@@ -1664,7 +1664,6 @@ static int qcom_slim_ngd_ctrl_probe(struct 
platform_device *pdev)
                 goto err_pdr_lookup;
         }

-       platform_driver_register(&qcom_slim_ngd_driver);
         return of_qcom_slim_ngd_register(dev, ctrl);

  err_pdr_alloc:
@@ -1754,6 +1753,23 @@ static struct platform_driver 
qcom_slim_ngd_driver = {
         },
  };

-module_platform_driver(qcom_slim_ngd_ctrl_driver);
+static struct platform_driver * const qcom_slim_ngd_drivers[] = {
+       /* Order here is important; ctrl last */
+       &qcom_slim_ngd_driver,
+       &qcom_slim_ngd_ctrl_driver,
+};
+
+static int __init qcom_slim_ngd_init(void)
+{
+       return platform_register_drivers(qcom_slim_ngd_drivers, 
ARRAY_SIZE(qcom_slim_ngd_drivers));
+}
+module_init(qcom_slim_ngd_init);
+
+static void __exit qcom_slim_ngd_exit(void)
+{
+       return platform_unregister_drivers(qcom_slim_ngd_drivers, 
ARRAY_SIZE(qcom_slim_ngd_drivers));
+}
+module_exit(qcom_slim_ngd_exit);
+
  MODULE_LICENSE("GPL v2");
  MODULE_DESCRIPTION("Qualcomm SLIMBus NGD controller");