Re: [PATCH 2/2] drm/i915/execlists: Explicitly reset both reg and context runtime

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On 26/03/2020 23:18, Chris Wilson wrote:
Upon a GPU reset, we copy the default context image over top of the
guilty image. This will rollback the CTX_TIMESTAMP register to before
our value of ce->runtime.last. Reset both back to 0 so that we do not
encounter an underflow on the next schedule out after resume.

This should not be a huge issue in practice, as hangs should be rare in
correct code.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
  drivers/gpu/drm/i915/gt/intel_lrc.c | 24 +++++++++++++-----------
  1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 4edda15eba26..47cec545a069 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -238,6 +238,17 @@ __execlists_update_reg_state(const struct intel_context *ce,
  			     const struct intel_engine_cs *engine,
  			     u32 head);
+static u32 intel_context_get_runtime(const struct intel_context *ce)
+{
+	/*
+	 * We can use either ppHWSP[16] which is recorded before the context
+	 * switch (and so excludes the cost of context switches) or use the
+	 * value from the context image itself, which is saved/restored earlier
+	 * and so includes the cost of the save.
+	 */
+	return READ_ONCE(ce->lrc_reg_state[CTX_TIMESTAMP]);
+}
+
  static void mark_eio(struct i915_request *rq)
  {
  	if (i915_request_completed(rq))
@@ -1154,6 +1165,7 @@ static void restore_default_state(struct intel_context *ce,
  		       engine->context_size - PAGE_SIZE);
execlists_init_reg_state(regs, ce, engine, ce->ring, false);
+	ce->runtime.last = intel_context_get_runtime(ce);
  }
static void reset_active(struct i915_request *rq,
@@ -1195,17 +1207,6 @@ static void reset_active(struct i915_request *rq,
  	ce->lrc_desc |= CTX_DESC_FORCE_RESTORE;
  }
-static u32 intel_context_get_runtime(const struct intel_context *ce)
-{
-	/*
-	 * We can use either ppHWSP[16] which is recorded before the context
-	 * switch (and so excludes the cost of context switches) or use the
-	 * value from the context image itself, which is saved/restored earlier
-	 * and so includes the cost of the save.
-	 */
-	return READ_ONCE(ce->lrc_reg_state[CTX_TIMESTAMP]);
-}
-
  static void st_update_runtime_underflow(struct intel_context *ce, s32 dt)
  {
  #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
@@ -4581,6 +4582,7 @@ static void init_common_reg_state(u32 * const regs,
  	regs[CTX_CONTEXT_CONTROL] = ctl;
regs[CTX_RING_CTL] = RING_CTL_SIZE(ring->size) | RING_VALID;
+	regs[CTX_TIMESTAMP] = 0;
  }
static void init_wa_bb_reg_state(u32 * const regs,


Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko
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