drm/i915/execlists: Always reset the context's RING registers

During reset, we try and stop the active ring. This has the consequence
that we often clobber the RING registers within the context image. When
we find an active request, we update the context image to rerun that
request (if it was guilty, we replace the hanging user payload with
NOPs). However, we were ignoring an active context if the request had
completed, with the consequence that the next submission on that request
would start with RING_HEAD==0 and not the tail of the previous request,
causing all requests still in the ring to be rerun. Rare, but
occasionally seen within CI where we would spot that the context seqno
would reverse and complain that we were retiring an incomplete request.

    <0> [412.390350]   <idle>-0       3d.s2 408373352us : __i915_request_submit: rcs0 fence 1e95b:3640 -> current 3638
    <0> [412.390350]   <idle>-0       3d.s2 408373353us : __i915_request_submit: rcs0 fence 1e95b:3642 -> current 3638
    <0> [412.390350]   <idle>-0       3d.s2 408373354us : __i915_request_submit: rcs0 fence 1e95b:3644 -> current 3638
    <0> [412.390350]   <idle>-0       3d.s2 408373354us : __i915_request_submit: rcs0 fence 1e95b:3646 -> current 3638
    <0> [412.390350]   <idle>-0       3d.s2 408373356us : __execlists_submission_tasklet: rcs0 in[0]:  ctx=2.1, fence 1e95b:3646 (current 3638), prio=4
    <0> [412.390350] i915_sel-4613    0.... 408373374us : __i915_request_commit: rcs0 fence 1e95b:3648
    <0> [412.390350] i915_sel-4613    0d..1 408373377us : process_csb: rcs0 cs-irq head=2, tail=3
    <0> [412.390350] i915_sel-4613    0d..1 408373377us : process_csb: rcs0 csb[3]: status=0x00000001:0x00000000, active=0x1
    <0> [412.390350] i915_sel-4613    0d..1 408373378us : __i915_request_submit: rcs0 fence 1e95b:3648 -> current 3638
    <0> [412.390350]   <idle>-0       3..s1 408373378us : execlists_submission_tasklet: rcs0 awake?=1, active=5
    <0> [412.390350] i915_sel-4613    0d..1 408373379us : __execlists_submission_tasklet: rcs0 in[0]:  ctx=2.2, fence 1e95b:3648 (current 3638), prio=4
    <0> [412.390350] i915_sel-4613    0.... 408373381us : i915_reset_engine: rcs0 flags=4
    <0> [412.390350] i915_sel-4613    0.... 408373382us : execlists_reset_prepare: rcs0: depth<-0
    <0> [412.390350]   <idle>-0       3d.s2 408373390us : process_csb: rcs0 cs-irq head=3, tail=4
    <0> [412.390350]   <idle>-0       3d.s2 408373390us : process_csb: rcs0 csb[4]: status=0x00008002:0x00000002, active=0x1
    <0> [412.390350]   <idle>-0       3d.s2 408373390us : process_csb: rcs0 out[0]: ctx=2.2, fence 1e95b:3648 (current 3640), prio=4
    <0> [412.390350] i915_sel-4613    0.... 408373401us : intel_engine_stop_cs: rcs0
    <0> [412.390350] i915_sel-4613    0d..1 408373402us : process_csb: rcs0 cs-irq head=4, tail=4
    <0> [412.390350] i915_sel-4613    0.... 408373403us : intel_gpu_reset: engine_mask=1
    <0> [412.390350] i915_sel-4613    0d..1 408373408us : execlists_cancel_port_requests: rcs0:port0 fence 1e95b:3648, (current 3648)
    <0> [412.390350] i915_sel-4613    0.... 408373442us : intel_engine_cancel_stop_cs: rcs0
    <0> [412.390350] i915_sel-4613    0.... 408373442us : execlists_reset_finish: rcs0: depth->0
    <0> [412.390350] ksoftirq-26      3..s. 408373442us : execlists_submission_tasklet: rcs0 awake?=1, active=0
    <0> [412.390350] ksoftirq-26      3d.s1 408373443us : process_csb: rcs0 cs-irq head=5, tail=5
    <0> [412.390350] i915_sel-4613    0.... 408373475us : i915_request_retire: rcs0 fence 1e95b:3640, current 3648
    <0> [412.390350] i915_sel-4613    0.... 408373476us : i915_request_retire: __retire_engine_request(rcs0) fence 1e95b:3640, current 3648
    <0> [412.390350] i915_sel-4613    0.... 408373494us : __i915_request_commit: rcs0 fence 1e95b:3650
    <0> [412.390350] i915_sel-4613    0d..1 408373496us : process_csb: rcs0 cs-irq head=5, tail=5
    <0> [412.390350] i915_sel-4613    0d..1 408373496us : __i915_request_submit: rcs0 fence 1e95b:3650 -> current 3648
    <0> [412.390350] i915_sel-4613    0d..1 408373498us : __execlists_submission_tasklet: rcs0 in[0]:  ctx=2.1, fence 1e95b:3650 (current 3648), prio=6
    <0> [412.390350] i915_sel-4613    0.... 408373500us : i915_request_retire_upto: rcs0 fence 1e95b:3648, current 3648
    <0> [412.390350] i915_sel-4613    0.... 408373500us : i915_request_retire: rcs0 fence 1e95b:3642, current 3648
    <0> [412.390350] i915_sel-4613    0.... 408373501us : i915_request_retire: __retire_engine_request(rcs0) fence 1e95b:3642, current 3648
    <0> [412.390350] i915_sel-4613    0.... 408373514us : i915_request_retire: rcs0 fence 1e95b:3644, current 3648
    <0> [412.390350] i915_sel-4613    0.... 408373515us : i915_request_retire: __retire_engine_request(rcs0) fence 1e95b:3644, current 3648
    <0> [412.390350] i915_sel-4613    0.... 408373527us : i915_request_retire: rcs0 fence 1e95b:3646, current 3640
    <0> [412.390350]   <idle>-0       3..s1 408373569us : execlists_submission_tasklet: rcs0 awake?=1, active=1
    <0> [412.390350]   <idle>-0       3d.s2 408373569us : process_csb: rcs0 cs-irq head=5, tail=1
    <0> [412.390350]   <idle>-0       3d.s2 408373570us : process_csb: rcs0 csb[0]: status=0x00000001:0x00000000, active=0x1
    <0> [412.390350]   <idle>-0       3d.s2 408373570us : process_csb: rcs0 csb[1]: status=0x00000018:0x00000002, active=0x5
    <0> [412.390350]   <idle>-0       3d.s2 408373570us : process_csb: rcs0 out[0]: ctx=2.1, fence 1e95b:3650 (current 3650), prio=6
    <0> [412.390350]   <idle>-0       3d.s2 408373571us : process_csb: rcs0 completed ctx=2
    <0> [412.390350] i915_sel-4613    0.... 408373621us : i915_request_retire: i915_request_retire:253 GEM_BUG_ON(!i915_request_completed(request))

v2: Fixup the cancellation path to drain the CSB and reset the pointers.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190411130515.20716-2-chris@chris-wilson.co.uk