With the new CSB processing code, we are not vulnerable to delayed
delivery of a pre-reset interrupt as we use the CSB status pointers in
the HWSP to decide if we need to parse any CSB events and no longer need
to wait for the first post-reset interrupt to be assured that the CSB
mmio registers are valid.

The new icl code to clear registers has a nasty lock inversion:
[   57.409776] ======================================================
[   57.409779] WARNING: possible circular locking dependency detected
[   57.409783] 4.18.0-rc4-CI-CI_DII_1137+ #1 Tainted: G     U  W
[   57.409785] ------------------------------------------------------
[   57.409788] swapper/6/0 is trying to acquire lock:
[   57.409790] 000000004f304ee5 (&engine->timeline.lock/1){-.-.}, at: execlists_submit_request+0x2b/0x1a0 [i915]
[   57.409841]
               but task is already holding lock:
[   57.409844] 00000000aad89594 (&(&rq->lock)->rlock#2){-.-.}, at: notify_ring+0x2b2/0x480 [i915]
[   57.409869]
               which lock already depends on the new lock.

[   57.409872]
               the existing dependency chain (in reverse order) is:
[   57.409876]
               -> #2 (&(&rq->lock)->rlock#2){-.-.}:
[   57.409900]        notify_ring+0x2b2/0x480 [i915]
[   57.409922]        gen8_cs_irq_handler+0x39/0xa0 [i915]
[   57.409943]        gen11_irq_handler+0x2f0/0x420 [i915]
[   57.409949]        __handle_irq_event_percpu+0x42/0x370
[   57.409952]        handle_irq_event_percpu+0x2b/0x70
[   57.409956]        handle_irq_event+0x2f/0x50
[   57.409959]        handle_edge_irq+0xe7/0x190
[   57.409964]        handle_irq+0x67/0x160
[   57.409967]        do_IRQ+0x5e/0x120
[   57.409971]        ret_from_intr+0x0/0x1d
[   57.409974]        _raw_spin_unlock_irqrestore+0x4e/0x60
[   57.409979]        tasklet_action_common.isra.5+0x47/0xb0
[   57.409982]        __do_softirq+0xd9/0x505
[   57.409985]        irq_exit+0xa9/0xc0
[   57.409988]        do_IRQ+0x9a/0x120
[   57.409991]        ret_from_intr+0x0/0x1d
[   57.409995]        cpuidle_enter_state+0xac/0x360
[   57.409999]        do_idle+0x1f3/0x250
[   57.410004]        cpu_startup_entry+0x6a/0x70
[   57.410010]        start_secondary+0x19d/0x1f0
[   57.410015]        secondary_startup_64+0xa5/0xb0
[   57.410018]
               -> #1 (&(&dev_priv->irq_lock)->rlock){-.-.}:
[   57.410081]        clear_gtiir+0x30/0x200 [i915]
[   57.410116]        execlists_reset+0x6e/0x2b0 [i915]
[   57.410140]        i915_reset_engine+0x111/0x190 [i915]
[   57.410165]        i915_handle_error+0x11a/0x4a0 [i915]
[   57.410198]        i915_hangcheck_elapsed+0x378/0x530 [i915]
[   57.410204]        process_one_work+0x248/0x6c0
[   57.410207]        worker_thread+0x37/0x380
[   57.410211]        kthread+0x119/0x130
[   57.410215]        ret_from_fork+0x3a/0x50
[   57.410217]
               -> #0 (&engine->timeline.lock/1){-.-.}:
[   57.410224]        _raw_spin_lock_irqsave+0x33/0x50
[   57.410256]        execlists_submit_request+0x2b/0x1a0 [i915]
[   57.410289]        submit_notify+0x8d/0x124 [i915]
[   57.410314]        __i915_sw_fence_complete+0x81/0x250 [i915]
[   57.410339]        dma_i915_sw_fence_wake+0xd/0x20 [i915]
[   57.410344]        dma_fence_signal_locked+0x79/0x200
[   57.410368]        notify_ring+0x2ba/0x480 [i915]
[   57.410392]        gen8_cs_irq_handler+0x39/0xa0 [i915]
[   57.410416]        gen11_irq_handler+0x2f0/0x420 [i915]
[   57.410421]        __handle_irq_event_percpu+0x42/0x370
[   57.410425]        handle_irq_event_percpu+0x2b/0x70
[   57.410428]        handle_irq_event+0x2f/0x50
[   57.410432]        handle_edge_irq+0xe7/0x190
[   57.410436]        handle_irq+0x67/0x160
[   57.410439]        do_IRQ+0x5e/0x120
[   57.410445]        ret_from_intr+0x0/0x1d
[   57.410449]        cpuidle_enter_state+0xac/0x360
[   57.410453]        do_idle+0x1f3/0x250
[   57.410456]        cpu_startup_entry+0x6a/0x70
[   57.410460]        start_secondary+0x19d/0x1f0
[   57.410464]        secondary_startup_64+0xa5/0xb0
[   57.410466]
               other info that might help us debug this:

[   57.410471] Chain exists of:
                 &engine->timeline.lock/1 --> &(&dev_priv->irq_lock)->rlock --> &(&rq->lock)->rlock#2

[   57.410481]  Possible unsafe locking scenario:

[   57.410485]        CPU0                    CPU1
[   57.410487]        ----                    ----
[   57.410490]   lock(&(&rq->lock)->rlock#2);
[   57.410494]                                lock(&(&dev_priv->irq_lock)->rlock);
[   57.410498]                                lock(&(&rq->lock)->rlock#2);
[   57.410503]   lock(&engine->timeline.lock/1);
[   57.410506]
                *** DEADLOCK ***

[   57.410511] 4 locks held by swapper/6/0:
[   57.410514]  #0: 0000000074575789 (&(&dev_priv->irq_lock)->rlock){-.-.}, at: gen11_irq_handler+0x8a/0x420 [i915]
[   57.410542]  #1: 000000009b29b30e (rcu_read_lock){....}, at: notify_ring+0x1a/0x480 [i915]
[   57.410573]  #2: 00000000aad89594 (&(&rq->lock)->rlock#2){-.-.}, at: notify_ring+0x2b2/0x480 [i915]
[   57.410601]  #3: 000000009b29b30e (rcu_read_lock){....}, at: submit_notify+0x35/0x124 [i915]
[   57.410635]
               stack backtrace:
[   57.410640] CPU: 6 PID: 0 Comm: swapper/6 Tainted: G     U  W         4.18.0-rc4-CI-CI_DII_1137+ #1
[   57.410644] Hardware name: Intel Corporation Ice Lake Client Platform/IceLake U DDR4 SODIMM PD RVP, BIOS ICLSFWR1.R00.2222.A01.1805300339 05/30/2018
[   57.410650] Call Trace:
[   57.410652]  <IRQ>
[   57.410657]  dump_stack+0x67/0x9b
[   57.410662]  print_circular_bug.isra.16+0x1c8/0x2b0
[   57.410666]  __lock_acquire+0x1897/0x1b50
[   57.410671]  ? lock_acquire+0xa6/0x210
[   57.410674]  lock_acquire+0xa6/0x210
[   57.410706]  ? execlists_submit_request+0x2b/0x1a0 [i915]
[   57.410711]  _raw_spin_lock_irqsave+0x33/0x50
[   57.410741]  ? execlists_submit_request+0x2b/0x1a0 [i915]
[   57.410769]  execlists_submit_request+0x2b/0x1a0 [i915]
[   57.410774]  ? _raw_spin_unlock_irqrestore+0x39/0x60
[   57.410804]  submit_notify+0x8d/0x124 [i915]
[   57.410828]  __i915_sw_fence_complete+0x81/0x250 [i915]
[   57.410854]  dma_i915_sw_fence_wake+0xd/0x20 [i915]
[   57.410858]  dma_fence_signal_locked+0x79/0x200
[   57.410882]  notify_ring+0x2ba/0x480 [i915]
[   57.410907]  gen8_cs_irq_handler+0x39/0xa0 [i915]
[   57.410933]  gen11_irq_handler+0x2f0/0x420 [i915]
[   57.410938]  __handle_irq_event_percpu+0x42/0x370
[   57.410943]  handle_irq_event_percpu+0x2b/0x70
[   57.410947]  handle_irq_event+0x2f/0x50
[   57.410951]  handle_edge_irq+0xe7/0x190
[   57.410955]  handle_irq+0x67/0x160
[   57.410958]  do_IRQ+0x5e/0x120
[   57.410962]  common_interrupt+0xf/0xf
[   57.410965]  </IRQ>
[   57.410969] RIP: 0010:cpuidle_enter_state+0xac/0x360
[   57.410972] Code: 44 00 00 31 ff e8 84 93 91 ff 45 84 f6 74 12 9c 58 f6 c4 02 0f 85 31 02 00 00 31 ff e8 7d 30 98 ff e8 e8 0e 94 ff fb 4c 29 fb <48> ba cf f7 53 e3 a5 9b c4 20 48 89 d8 48 c1 fb 3f 48 f7 ea b8 ff
[   57.411015] RSP: 0018:ffffc90000133e90 EFLAGS: 00000216 ORIG_RAX: ffffffffffffffdd
[   57.411023] RAX: ffff8804ae748040 RBX: 000000000002a97d RCX: 0000000000000000
[   57.411029] RDX: 0000000000000046 RSI: ffffffff82141263 RDI: ffffffff820f05a7
[   57.411035] RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
[   57.411041] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8229f078
[   57.411045] R13: ffff8804ab2adfa8 R14: 0000000000000000 R15: 0000000d5de092e3
[   57.411052]  do_idle+0x1f3/0x250
[   57.411055]  cpu_startup_entry+0x6a/0x70
[   57.411059]  start_secondary+0x19d/0x1f0
[   57.411064]  secondary_startup_64+0xa5/0xb0

The easiest remedy is to remove the defunct code.

Fixes: ff047a87 ("drm/i915/icl: Correctly clear lost ctx-switch interrupts across reset for Gen11")
References: fd8526e5

 ("drm/i915/execlists: Trust the CSB")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180713203529.1973-3-chris@chris-wilson.co.uk