drm/mst: Don't do atomic checks over disabled managers

When a main MST port is disconnected drivers should call
drm_dp_mst_topology_mgr_set_mst() disabling the MST manager, this
function will set manager mst_primary to NULL and it will cause the
crash bellow on the next atomic check when trying to access
mst_primary->port.

As there is no use in running checks over managers that are not
active this patch will skip it.

[  305.616450] [drm:drm_dp_mst_atomic_check] [MST PORT:00000000cc2049e9] releases all VCPI slots
[  305.625085] [drm:drm_dp_mst_atomic_check] [MST PORT:00000000020ab43e] releases all VCPI slots
[  305.633729] [drm:drm_dp_mst_atomic_check] [MST MGR:00000000cdd467d4] mst state 00000000b67672eb VCPI avail=63 used=0
[  305.644405] BUG: kernel NULL pointer dereference, address: 0000000000000030
[  305.651448] #PF: supervisor read access in kernel mode
[  305.656640] #PF: error_code(0x0000) - not-present page
[  305.661807] PGD 0 P4D 0
[  305.664396] Oops: 0000 [#1] PREEMPT SMP NOPTI
[  305.668789] CPU: 3 PID: 183 Comm: kworker/3:2 Not tainted 5.5.0-rc6+ #1404
[  305.675703] Hardware name: Intel Corporation Ice Lake Client Platform/IceLake U DDR4 SODIMM PD RVP TLC, BIOS ICLSFWR1.R00.3201.A00.1905140358 05/14/2019
[  305.689425] Workqueue: events drm_dp_delayed_destroy_work
[  305.694874] RIP: 0010:drm_dp_mst_atomic_check+0x138/0x2c0
[  305.700306] Code: 00 00 00 41 29 d9 41 89 d8 4c 89 fa 4c 89 f1 48 c7 c6 b0 b1 34 82 bf 10 00 00 00 45 31 ed e8 3f 99 02 00 4d 8b bf 80 04 00 00 <49> 8b 47 30 49 8d 5f 30 4c 8d 60 e8 48 39 c3 74 35 49 8b 7c 24 28
[  305.719169] RSP: 0018:ffffc90001687b58 EFLAGS: 00010246
[  305.724434] RAX: 0000000000000000 RBX: 000000000000003f RCX: 0000000000000000
[  305.731611] RDX: 0000000000000000 RSI: ffff88849fba8cb8 RDI: 00000000ffffffff
[  305.738785] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
[  305.745962] R10: ffffc900016879a0 R11: ffffc900016879a5 R12: 0000000000000000
[  305.753139] R13: 0000000000000000 R14: ffff8884905c9bc0 R15: 0000000000000000
[  305.760315] FS:  0000000000000000(0000) GS:ffff88849fb80000(0000) knlGS:0000000000000000
[  305.768452] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  305.774263] CR2: 0000000000000030 CR3: 0000000005610006 CR4: 0000000000760ee0
[  305.781441] PKRU: 55555554
[  305.784228] Call Trace:
[  305.786739]  intel_atomic_check+0xb2e/0x2560 [i915]
[  305.791678]  ? printk+0x53/0x6a
[  305.794856]  ? drm_atomic_check_only+0x3e/0x810
[  305.799417]  ? __drm_dbg+0x82/0x90
[  305.802848]  drm_atomic_check_only+0x56a/0x810
[  305.807322]  drm_atomic_commit+0xe/0x50
[  305.811185]  drm_client_modeset_commit_atomic+0x1e2/0x250
[  305.816619]  drm_client_modeset_commit_force+0x4d/0x180
[  305.821921]  drm_fb_helper_restore_fbdev_mode_unlocked+0x46/0xa0
[  305.827963]  drm_fb_helper_set_par+0x2b/0x40
[  305.832265]  drm_fb_helper_hotplug_event.part.0+0xb2/0xd0
[  305.837755]  drm_kms_helper_hotplug_event+0x21/0x30
[  305.842694]  process_one_work+0x25b/0x5b0
[  305.846735]  worker_thread+0x4b/0x3b0
[  305.850439]  kthread+0x100/0x140
[  305.853690]  ? process_one_work+0x5b0/0x5b0
[  305.857901]  ? kthread_park+0x80/0x80
[  305.861588]  ret_from_fork+0x24/0x50
[  305.865202] Modules linked in: snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic i915 btusb btrtl btbcm btintel bluetooth prime_numbers snd_hda_intel snd_intel_dspcfg snd_hda_codec e1000e snd_hwdep snd_hda_core thunderbolt mei_hdcp mei_me asix cdc_ether x86_pkg_temp_thermal r8152 mei coretemp usbnet snd_pcm mii crct10dif_pclmul ptp crc32_pclmul ecdh_generic ghash_clmulni_intel pps_core ecc i2c_i801 intel_lpss_pci
[  305.903096] CR2: 0000000000000030
[  305.906431] ---[ end trace 70ee364eed801cb0 ]---
[  305.940816] RIP: 0010:drm_dp_mst_atomic_check+0x138/0x2c0
[  305.946261] Code: 00 00 00 41 29 d9 41 89 d8 4c 89 fa 4c 89 f1 48 c7 c6 b0 b1 34 82 bf 10 00 00 00 45 31 ed e8 3f 99 02 00 4d 8b bf 80 04 00 00 <49> 8b 47 30 49 8d 5f 30 4c 8d 60 e8 48 39 c3 74 35 49 8b 7c 24 28
[  305.965125] RSP: 0018:ffffc90001687b58 EFLAGS: 00010246
[  305.970382] RAX: 0000000000000000 RBX: 000000000000003f RCX: 0000000000000000
[  305.977571] RDX: 0000000000000000 RSI: ffff88849fba8cb8 RDI: 00000000ffffffff
[  305.984747] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
[  305.991921] R10: ffffc900016879a0 R11: ffffc900016879a5 R12: 0000000000000000
[  305.999099] R13: 0000000000000000 R14: ffff8884905c9bc0 R15: 0000000000000000
[  306.006271] FS:  0000000000000000(0000) GS:ffff88849fb80000(0000) knlGS:0000000000000000
[  306.014407] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  306.020185] CR2: 0000000000000030 CR3: 000000048b3aa003 CR4: 0000000000760ee0
[  306.027404] PKRU: 55555554
[  306.030127] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:38
[  306.039049] in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 183, name: kworker/3:2
[  306.047272] INFO: lockdep is turned off.
[  306.051217] irq event stamp: 77505
[  306.054647] hardirqs last  enabled at (77505): [<ffffffff81a0c147>] _raw_spin_unlock_irqrestore+0x47/0x60
[  306.064270] hardirqs last disabled at (77504): [<ffffffff81a0bedf>] _raw_spin_lock_irqsave+0xf/0x50
[  306.073404] softirqs last  enabled at (77402): [<ffffffff81e00389>] __do_softirq+0x389/0x47f
[  306.081885] softirqs last disabled at (77395): [<ffffffff810b83a9>] irq_exit+0xa9/0xc0
[  306.089859] CPU: 3 PID: 183 Comm: kworker/3:2 Tainted: G      D           5.5.0-rc6+ #1404
[  306.098167] Hardware name: Intel Corporation Ice Lake Client Platform/IceLake U DDR4 SODIMM PD RVP TLC, BIOS ICLSFWR1.R00.3201.A00.1905140358 05/14/2019
[  306.111882] Workqueue: events drm_dp_delayed_destroy_work
[  306.117314] Call Trace:
[  306.119780]  dump_stack+0x71/0xa0
[  306.123135]  ___might_sleep.cold+0xf7/0x10b
[  306.127399]  exit_signals+0x2b/0x360
[  306.131014]  do_exit+0xa7/0xc70
[  306.134189]  ? kthread+0x100/0x140
[  306.137615]  rewind_stack_do_exit+0x17/0x20

Fixes: cd82d82c ("drm/dp_mst: Add branch bandwidth validation to MST atomic check")
Cc: Mikita Lipski <mikita.lipski@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Lyude Paul <lyude@redhat.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -5001,6 +5001,9 @@ int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
 	int i, ret = 0;
 
 	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
+		if (!mgr->mst_state)
+			continue;
+
 		ret = drm_dp_mst_atomic_check_vcpi_alloc_limit(mgr, mst_state);
 		if (ret)
 			break;