[PATCH 2/3] drm/i915: Allow userspace to specify ringsize on construction

[Chris Wilson <chris@chris-wilson.co.uk>]

No good reason why we must always use a static ringsize, so let
userspace select one during construction.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_context.c | 139 +++++++++++++++++++-
 drivers/gpu/drm/i915/gt/intel_lrc.c         |   1 +
 include/uapi/drm/i915_drm.h                 |  19 +++
 3 files changed, 153 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index 1284f47303fa..ee9a4634fed8 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -597,23 +597,30 @@ __create_context(struct drm_i915_private *i915)
 	return ERR_PTR(err);
 }
 
-static void
+static int
 context_apply_all(struct i915_gem_context *ctx,
-		  void (*fn)(struct intel_context *ce, void *data),
+		  int (*fn)(struct intel_context *ce, void *data),
 		  void *data)
 {
 	struct i915_gem_engines_iter it;
 	struct intel_context *ce;
+	int err = 0;
 
-	for_each_gem_engine(ce, i915_gem_context_lock_engines(ctx), it)
-		fn(ce, data);
+	for_each_gem_engine(ce, i915_gem_context_lock_engines(ctx), it) {
+		err = fn(ce, data);
+		if (err)
+			break;
+	}
 	i915_gem_context_unlock_engines(ctx);
+
+	return err;
 }
 
-static void __apply_ppgtt(struct intel_context *ce, void *vm)
+static int __apply_ppgtt(struct intel_context *ce, void *vm)
 {
 	i915_vm_put(ce->vm);
 	ce->vm = i915_vm_get(vm);
+	return 0;
 }
 
 static struct i915_address_space *
@@ -651,9 +658,10 @@ static void __set_timeline(struct intel_timeline **dst,
 		intel_timeline_put(old);
 }
 
-static void __apply_timeline(struct intel_context *ce, void *timeline)
+static int __apply_timeline(struct intel_context *ce, void *timeline)
 {
 	__set_timeline(&ce->timeline, timeline);
+	return 0;
 }
 
 static void __assign_timeline(struct i915_gem_context *ctx,
@@ -1223,6 +1231,104 @@ static int set_ppgtt(struct drm_i915_file_private *file_priv,
 	return err;
 }
 
+static int __apply_ringsize(struct intel_context *ce, void *sz)
+{
+	int err;
+
+	err = i915_active_wait(&ce->active);
+	if (err < 0)
+		return err;
+
+	if (intel_context_lock_pinned(ce))
+		return -EINTR;
+
+	if (intel_context_is_pinned(ce)) {
+		err = -EBUSY; /* In active use, come back later! */
+		goto unlock;
+	}
+
+	if (test_bit(CONTEXT_ALLOC_BIT, &ce->flags)) {
+		struct intel_ring *ring;
+
+		/* Replace the existing ringbuffer */
+		ring = intel_engine_create_ring(ce->engine,
+						(unsigned long)sz);
+		if (IS_ERR(ring)) {
+			err = PTR_ERR(ring);
+			goto unlock;
+		}
+
+		intel_ring_put(ce->ring);
+		ce->ring = ring;
+
+		/* Context image will be updated on next pin */
+	} else {
+		ce->ring = sz;
+	}
+
+unlock:
+	intel_context_unlock_pinned(ce);
+	return err;
+}
+
+static int set_ringsize(struct i915_gem_context *ctx,
+			struct drm_i915_gem_context_param *args)
+{
+	if (!HAS_LOGICAL_RING_CONTEXTS(ctx->i915))
+		return -ENODEV;
+
+	if (args->size)
+		return -EINVAL;
+
+	if (!IS_ALIGNED(args->value, I915_GTT_PAGE_SIZE))
+		return -EINVAL;
+
+	if (args->value < I915_GTT_PAGE_SIZE)
+		return -EINVAL;
+
+	if (args->value > 128 * I915_GTT_PAGE_SIZE)
+		return -EINVAL;
+
+	return context_apply_all(ctx,
+				 __apply_ringsize,
+				 __intel_context_ring_size(args->value));
+}
+
+static int __get_ringsize(struct intel_context *ce, void *arg)
+{
+	int num_pages;
+
+	if (intel_context_lock_pinned(ce))
+		return -EINTR;
+
+	if (test_bit(CONTEXT_ALLOC_BIT, &ce->flags))
+		num_pages = ce->ring->size / I915_GTT_PAGE_SIZE;
+	else
+		num_pages = (uintptr_t)ce->ring / I915_GTT_PAGE_SIZE;
+
+	intel_context_unlock_pinned(ce);
+	return num_pages; /* stop on first engine */
+}
+
+static int get_ringsize(struct i915_gem_context *ctx,
+			struct drm_i915_gem_context_param *args)
+{
+	int num_pages;
+
+	if (!HAS_LOGICAL_RING_CONTEXTS(ctx->i915))
+		return -ENODEV;
+
+	if (args->size)
+		return -EINVAL;
+
+	num_pages = context_apply_all(ctx, __get_ringsize, NULL);
+	if (num_pages < 0)
+		return num_pages;
+
+	args->value = (u64)num_pages * I915_GTT_PAGE_SIZE;
+	return 0;
+}
+
 static int gen8_emit_rpcs_config(struct i915_request *rq,
 				 struct intel_context *ce,
 				 struct intel_sseu sseu)
@@ -1935,6 +2041,10 @@ static int ctx_setparam(struct drm_i915_file_private *fpriv,
 		ret = set_persistence(ctx, args);
 		break;
 
+	case I915_CONTEXT_PARAM_RINGSIZE:
+		ret = set_ringsize(ctx, args);
+		break;
+
 	case I915_CONTEXT_PARAM_BAN_PERIOD:
 	default:
 		ret = -EINVAL;
@@ -2003,6 +2113,19 @@ static int clone_engines(struct i915_gem_context *dst,
 			__free_engines(clone, n);
 			goto err_unlock;
 		}
+
+		/* Copy across the preferred ringsize */
+		clone->engines[n]->ring = e->engines[n]->ring;
+		if (test_bit(CONTEXT_ALLOC_BIT, &e->engines[n]->flags)) {
+			if (intel_context_lock_pinned(e->engines[n])) {
+				__free_engines(clone, n + 1);
+				goto err_unlock;
+			}
+
+			clone->engines[n]->ring =
+				__intel_context_ring_size(e->engines[n]->ring->size);
+			intel_context_unlock_pinned(e->engines[n]);
+		}
 	}
 	clone->num_engines = n;
 
@@ -2366,6 +2489,10 @@ int i915_gem_context_getparam_ioctl(struct drm_device *dev, void *data,
 		args->value = i915_gem_context_is_persistent(ctx);
 		break;
 
+	case I915_CONTEXT_PARAM_RINGSIZE:
+		ret = get_ringsize(ctx, args);
+		break;
+
 	case I915_CONTEXT_PARAM_BAN_PERIOD:
 	default:
 		ret = -EINVAL;
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 33ce258d484f..2649690a951e 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -2417,6 +2417,7 @@ __execlists_update_reg_state(const struct intel_context *ce,
 	regs[CTX_RING_START] = i915_ggtt_offset(ring->vma);
 	regs[CTX_RING_HEAD] = ring->head;
 	regs[CTX_RING_TAIL] = ring->tail;
+	regs[CTX_RING_CTL] = RING_CTL_SIZE(ring->size) | RING_VALID;
 
 	/* RPCS */
 	if (engine->class == RENDER_CLASS) {
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 5400d7e057f1..ae7cd681b075 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1587,6 +1587,25 @@ struct drm_i915_gem_context_param {
  * By default, new contexts allow persistence.
  */
 #define I915_CONTEXT_PARAM_PERSISTENCE	0xb
+
+/*
+ * I915_CONTEXT_PARAM_RINGSIZE:
+ *
+ * Sets the size of the CS ringbuffer to use for logical ring contexts. This
+ * applies a limit of how many batches can be queued to HW before the caller
+ * is blocked due to lack of space for more commands.
+ *
+ * Only reliably possible to be set prior to first use, i.e. during
+ * construction. At any later point, the current execution must be flushed as
+ * the ring can only be changed while the context is idle.
+ *
+ * Only applies to the current set of engine and lost when those engines
+ * are replaced by a new mapping (see I915_CONTEXT_PARAM_ENGINES).
+ *
+ * Must be between 4 - 512 KiB, in intervals of page size [4 KiB].
+ * Default is 16 KiB.
+ */
+#define I915_CONTEXT_PARAM_RINGSIZE	0xc
 /* Must be kept compact -- no holes and well documented */
 
 	__u64 value;
-- 
2.24.0

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