drm/i915: Match code to comment and enforce ppgtt for execlists

Our execlist dispatch code requires a ppGTT so make sure we enforce that
option in intel_sanitize_enable_ppgtt(). The comment already tries to
explain that execlists requires ppgtt, but was written when gen8 may
have also taken the legacy path; so rewrite the code to match the
comment by using HAS_EXECLISTS() feature instead of the gen.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180922141804.21183-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -152,10 +152,10 @@ int intel_sanitize_enable_ppgtt(struct drm_i915_private *dev_priv,
 	}
 
 	/*
-	 * We don't allow disabling PPGTT for gen9+ as it's a requirement for
+	 * We don't allow disabling PPGTT for gen8+ as it's a requirement for
 	 * execlists, the sole mechanism available to submit work.
 	 */
-	if (enable_ppgtt == 0 && INTEL_GEN(dev_priv) < 9)
+	if (enable_ppgtt == 0 && !HAS_EXECLISTS(dev_priv))
 		return 0;
 
 	if (enable_ppgtt == 1)

drivers/gpu/drm/i915/intel_lrc.c

@@ -430,7 +430,7 @@ static u64 execlists_update_context(struct i915_request *rq)
 	 * PML4 is allocated during ppgtt init, so this is not needed
 	 * in 48-bit mode.
 	 */
-	if (ppgtt && !i915_vm_is_48bit(&ppgtt->vm))
+	if (!i915_vm_is_48bit(&ppgtt->vm))
 		execlists_update_context_pdps(ppgtt, reg_state);
 
 	return ce->lrc_desc;
@@ -1376,6 +1376,7 @@ execlists_context_pin(struct intel_engine_cs *engine,
 	struct intel_context *ce = to_intel_context(ctx, engine);
 
 	lockdep_assert_held(&ctx->i915->drm.struct_mutex);
+	GEM_BUG_ON(!(ctx->ppgtt ?: ctx->i915->mm.aliasing_ppgtt));
 
 	if (likely(ce->pin_count++))
 		return ce;
@@ -2705,7 +2706,7 @@ static void execlists_init_reg_state(u32 *regs,
 	CTX_REG(regs, CTX_PDP0_UDW, GEN8_RING_PDP_UDW(engine, 0), 0);
 	CTX_REG(regs, CTX_PDP0_LDW, GEN8_RING_PDP_LDW(engine, 0), 0);
 
-	if (ppgtt && i915_vm_is_48bit(&ppgtt->vm)) {
+	if (i915_vm_is_48bit(&ppgtt->vm)) {
 		/* 64b PPGTT (48bit canonical)
 		 * PDP0_DESCRIPTOR contains the base address to PML4 and
 		 * other PDP Descriptors are ignored.