net: dsa: qca: ar9331: fix sleeping function called from invalid context bug

With lockdep enabled, we will get following warning:

 ar9331_switch ethernet.1:10 lan0 (uninitialized): PHY [!ahb!ethernet@1a000000!mdio!switch@10:00] driver [Qualcomm Atheros AR9331 built-in PHY] (irq=13)
 BUG: sleeping function called from invalid context at kernel/locking/mutex.c:935
 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 18, name: kworker/0:1
 INFO: lockdep is turned off.
 irq event stamp: 602
 hardirqs last  enabled at (601): [<8073fde0>] _raw_spin_unlock_irq+0x3c/0x80
 hardirqs last disabled at (602): [<8073a4f4>] __schedule+0x184/0x800
 softirqs last  enabled at (0): [<80080f60>] copy_process+0x578/0x14c8
 softirqs last disabled at (0): [<00000000>] 0x0
 CPU: 0 PID: 18 Comm: kworker/0:1 Not tainted 5.10.0-rc3-ar9331-00734-g7d644991df0c #31
 Workqueue: events deferred_probe_work_func
 Stack : 80980000 80980000 8089ef70 80890000 804b5414 80980000 00000002 80b53728
         00000000 800d1268 804b5414 ffffffde 00000017 800afe08 81943860 0f5bfc32
         00000000 00000000 8089ef70 819436c0 ffffffea 00000000 00000000 00000000
         8194390c 808e353c 0000000f 66657272 80980000 00000000 00000000 80890000
         804b5414 80980000 00000002 80b53728 00000000 00000000 00000000 80d40000
         ...
 Call Trace:
 [<80069ce0>] show_stack+0x9c/0x140
 [<800afe08>] ___might_sleep+0x220/0x244
 [<8073bfb0>] __mutex_lock+0x70/0x374
 [<8073c2e0>] mutex_lock_nested+0x2c/0x38
 [<804b5414>] regmap_update_bits_base+0x38/0x8c
 [<804ee584>] regmap_update_bits+0x1c/0x28
 [<804ee714>] ar9331_sw_unmask_irq+0x34/0x60
 [<800d91f0>] unmask_irq+0x48/0x70
 [<800d93d4>] irq_startup+0x114/0x11c
 [<800d65b4>] __setup_irq+0x4f4/0x6d0
 [<800d68a0>] request_threaded_irq+0x110/0x190
 [<804e3ef0>] phy_request_interrupt+0x4c/0xe4
 [<804df508>] phylink_bringup_phy+0x2c0/0x37c
 [<804df7bc>] phylink_of_phy_connect+0x118/0x130
 [<806c1a64>] dsa_slave_create+0x3d0/0x578
 [<806bc4ec>] dsa_register_switch+0x934/0xa20
 [<804eef98>] ar9331_sw_probe+0x34c/0x364
 [<804eb48c>] mdio_probe+0x44/0x70
 [<8049e3b4>] really_probe+0x30c/0x4f4
 [<8049ea10>] driver_probe_device+0x264/0x26c
 [<8049bc10>] bus_for_each_drv+0xb4/0xd8
 [<8049e684>] __device_attach+0xe8/0x18c
 [<8049ce58>] bus_probe_device+0x48/0xc4
 [<8049db70>] deferred_probe_work_func+0xdc/0xf8
 [<8009ff64>] process_one_work+0x2e4/0x4a0
 [<800a0770>] worker_thread+0x2a8/0x354
 [<800a774c>] kthread+0x16c/0x174
 [<8006306c>] ret_from_kernel_thread+0x14/0x1c

 ar9331_switch ethernet.1:10 lan1 (uninitialized): PHY [!ahb!ethernet@1a000000!mdio!switch@10:02] driver [Qualcomm Atheros AR9331 built-in PHY] (irq=13)
 DSA: tree 0 setup

To fix it, it is better to move access to MDIO register to the .irq_bus_sync_unlock
call back.

Fixes: ec6698c2 ("net: dsa: add support for Atheros AR9331 built-in switch")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20201211110317.17061-1-o.rempel@pengutronix.de


Signed-off-by: Jakub Kicinski <kuba@kernel.org>