Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright © 2011-2012 Intel Corporation |
| 3 | * |
| 4 | * Permission is hereby granted, free of charge, to any person obtaining a |
| 5 | * copy of this software and associated documentation files (the "Software"), |
| 6 | * to deal in the Software without restriction, including without limitation |
| 7 | * the rights to use, copy, modify, merge, publish, distribute, sublicense, |
| 8 | * and/or sell copies of the Software, and to permit persons to whom the |
| 9 | * Software is furnished to do so, subject to the following conditions: |
| 10 | * |
| 11 | * The above copyright notice and this permission notice (including the next |
| 12 | * paragraph) shall be included in all copies or substantial portions of the |
| 13 | * Software. |
| 14 | * |
| 15 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
| 16 | * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
| 17 | * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL |
| 18 | * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
| 19 | * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING |
| 20 | * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS |
| 21 | * IN THE SOFTWARE. |
| 22 | * |
| 23 | * Authors: |
| 24 | * Ben Widawsky <ben@bwidawsk.net> |
| 25 | * |
| 26 | */ |
| 27 | |
| 28 | /* |
| 29 | * This file implements HW context support. On gen5+ a HW context consists of an |
| 30 | * opaque GPU object which is referenced at times of context saves and restores. |
| 31 | * With RC6 enabled, the context is also referenced as the GPU enters and exists |
| 32 | * from RC6 (GPU has it's own internal power context, except on gen5). Though |
| 33 | * something like a context does exist for the media ring, the code only |
| 34 | * supports contexts for the render ring. |
| 35 | * |
| 36 | * In software, there is a distinction between contexts created by the user, |
| 37 | * and the default HW context. The default HW context is used by GPU clients |
| 38 | * that do not request setup of their own hardware context. The default |
| 39 | * context's state is never restored to help prevent programming errors. This |
| 40 | * would happen if a client ran and piggy-backed off another clients GPU state. |
| 41 | * The default context only exists to give the GPU some offset to load as the |
| 42 | * current to invoke a save of the context we actually care about. In fact, the |
| 43 | * code could likely be constructed, albeit in a more complicated fashion, to |
| 44 | * never use the default context, though that limits the driver's ability to |
| 45 | * swap out, and/or destroy other contexts. |
| 46 | * |
| 47 | * All other contexts are created as a request by the GPU client. These contexts |
| 48 | * store GPU state, and thus allow GPU clients to not re-emit state (and |
| 49 | * potentially query certain state) at any time. The kernel driver makes |
| 50 | * certain that the appropriate commands are inserted. |
| 51 | * |
| 52 | * The context life cycle is semi-complicated in that context BOs may live |
| 53 | * longer than the context itself because of the way the hardware, and object |
| 54 | * tracking works. Below is a very crude representation of the state machine |
| 55 | * describing the context life. |
| 56 | * refcount pincount active |
| 57 | * S0: initial state 0 0 0 |
| 58 | * S1: context created 1 0 0 |
| 59 | * S2: context is currently running 2 1 X |
| 60 | * S3: GPU referenced, but not current 2 0 1 |
| 61 | * S4: context is current, but destroyed 1 1 0 |
| 62 | * S5: like S3, but destroyed 1 0 1 |
| 63 | * |
| 64 | * The most common (but not all) transitions: |
| 65 | * S0->S1: client creates a context |
| 66 | * S1->S2: client submits execbuf with context |
| 67 | * S2->S3: other clients submits execbuf with context |
| 68 | * S3->S1: context object was retired |
| 69 | * S3->S2: clients submits another execbuf |
| 70 | * S2->S4: context destroy called with current context |
| 71 | * S3->S5->S0: destroy path |
| 72 | * S4->S5->S0: destroy path on current context |
| 73 | * |
| 74 | * There are two confusing terms used above: |
| 75 | * The "current context" means the context which is currently running on the |
| 76 | * GPU. The GPU has loaded it's state already and has stored away the gtt |
| 77 | * offset of the BO. The GPU is not actively referencing the data at this |
| 78 | * offset, but it will on the next context switch. The only way to avoid this |
| 79 | * is to do a GPU reset. |
| 80 | * |
| 81 | * An "active context' is one which was previously the "current context" and is |
| 82 | * on the active list waiting for the next context switch to occur. Until this |
| 83 | * happens, the object must remain at the same gtt offset. It is therefore |
| 84 | * possible to destroy a context, but it is still active. |
| 85 | * |
| 86 | */ |
| 87 | |
| 88 | #include "drmP.h" |
| 89 | #include "i915_drm.h" |
| 90 | #include "i915_drv.h" |
| 91 | |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 92 | /* This is a HW constraint. The value below is the largest known requirement |
| 93 | * I've seen in a spec to date, and that was a workaround for a non-shipping |
| 94 | * part. It should be safe to decrease this, but it's more future proof as is. |
| 95 | */ |
| 96 | #define CONTEXT_ALIGN (64<<10) |
| 97 | |
| 98 | static struct i915_hw_context * |
| 99 | i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id); |
| 100 | |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 101 | static int get_context_size(struct drm_device *dev) |
| 102 | { |
| 103 | struct drm_i915_private *dev_priv = dev->dev_private; |
| 104 | int ret; |
| 105 | u32 reg; |
| 106 | |
| 107 | switch (INTEL_INFO(dev)->gen) { |
| 108 | case 6: |
| 109 | reg = I915_READ(CXT_SIZE); |
| 110 | ret = GEN6_CXT_TOTAL_SIZE(reg) * 64; |
| 111 | break; |
| 112 | case 7: |
| 113 | reg = I915_READ(GEN7_CTX_SIZE); |
| 114 | ret = GEN7_CTX_TOTAL_SIZE(reg) * 64; |
| 115 | break; |
| 116 | default: |
| 117 | BUG(); |
| 118 | } |
| 119 | |
| 120 | return ret; |
| 121 | } |
| 122 | |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 123 | static void do_destroy(struct i915_hw_context *ctx) |
| 124 | { |
| 125 | struct drm_device *dev = ctx->obj->base.dev; |
| 126 | struct drm_i915_private *dev_priv = dev->dev_private; |
| 127 | |
| 128 | if (ctx->file_priv) |
| 129 | idr_remove(&ctx->file_priv->context_idr, ctx->id); |
| 130 | else |
| 131 | BUG_ON(ctx != dev_priv->ring[RCS].default_context); |
| 132 | |
| 133 | drm_gem_object_unreference(&ctx->obj->base); |
| 134 | kfree(ctx); |
| 135 | } |
| 136 | |
| 137 | static int |
| 138 | create_hw_context(struct drm_device *dev, |
| 139 | struct drm_i915_file_private *file_priv, |
| 140 | struct i915_hw_context **ctx_out) |
| 141 | { |
| 142 | struct drm_i915_private *dev_priv = dev->dev_private; |
| 143 | int ret, id; |
| 144 | |
| 145 | *ctx_out = kzalloc(sizeof(struct drm_i915_file_private), GFP_KERNEL); |
| 146 | if (*ctx_out == NULL) |
| 147 | return -ENOMEM; |
| 148 | |
| 149 | (*ctx_out)->obj = i915_gem_alloc_object(dev, |
| 150 | dev_priv->hw_context_size); |
| 151 | if ((*ctx_out)->obj == NULL) { |
| 152 | kfree(*ctx_out); |
| 153 | DRM_DEBUG_DRIVER("Context object allocated failed\n"); |
| 154 | return -ENOMEM; |
| 155 | } |
| 156 | |
| 157 | /* The ring associated with the context object is handled by the normal |
| 158 | * object tracking code. We give an initial ring value simple to pass an |
| 159 | * assertion in the context switch code. |
| 160 | */ |
| 161 | (*ctx_out)->ring = &dev_priv->ring[RCS]; |
| 162 | |
| 163 | /* Default context will never have a file_priv */ |
| 164 | if (file_priv == NULL) |
| 165 | return 0; |
| 166 | |
| 167 | (*ctx_out)->file_priv = file_priv; |
| 168 | |
| 169 | again: |
| 170 | if (idr_pre_get(&file_priv->context_idr, GFP_KERNEL) == 0) { |
| 171 | ret = -ENOMEM; |
| 172 | DRM_DEBUG_DRIVER("idr allocation failed\n"); |
| 173 | goto err_out; |
| 174 | } |
| 175 | |
| 176 | ret = idr_get_new_above(&file_priv->context_idr, *ctx_out, |
| 177 | DEFAULT_CONTEXT_ID + 1, &id); |
| 178 | if (ret == 0) |
| 179 | (*ctx_out)->id = id; |
| 180 | |
| 181 | if (ret == -EAGAIN) |
| 182 | goto again; |
| 183 | else if (ret) |
| 184 | goto err_out; |
| 185 | |
| 186 | return 0; |
| 187 | |
| 188 | err_out: |
| 189 | do_destroy(*ctx_out); |
| 190 | return ret; |
| 191 | } |
| 192 | |
Ben Widawsky | e055684 | 2012-06-04 14:42:46 -0700 | [diff] [blame] | 193 | static inline bool is_default_context(struct i915_hw_context *ctx) |
| 194 | { |
| 195 | return (ctx == ctx->ring->default_context); |
| 196 | } |
| 197 | |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 198 | /** |
| 199 | * The default context needs to exist per ring that uses contexts. It stores the |
| 200 | * context state of the GPU for applications that don't utilize HW contexts, as |
| 201 | * well as an idle case. |
| 202 | */ |
| 203 | static int create_default_context(struct drm_i915_private *dev_priv) |
| 204 | { |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 205 | struct i915_hw_context *ctx; |
| 206 | int ret; |
| 207 | |
| 208 | BUG_ON(!mutex_is_locked(&dev_priv->dev->struct_mutex)); |
| 209 | |
| 210 | ret = create_hw_context(dev_priv->dev, NULL, |
| 211 | &dev_priv->ring[RCS].default_context); |
| 212 | if (ret) |
| 213 | return ret; |
| 214 | |
| 215 | /* We may need to do things with the shrinker which require us to |
| 216 | * immediately switch back to the default context. This can cause a |
| 217 | * problem as pinning the default context also requires GTT space which |
| 218 | * may not be available. To avoid this we always pin the |
| 219 | * default context. |
| 220 | */ |
| 221 | ctx = dev_priv->ring[RCS].default_context; |
| 222 | ret = i915_gem_object_pin(ctx->obj, CONTEXT_ALIGN, false); |
| 223 | if (ret) { |
| 224 | do_destroy(ctx); |
| 225 | return ret; |
| 226 | } |
| 227 | |
| 228 | return ret; |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 229 | } |
| 230 | |
| 231 | void i915_gem_context_init(struct drm_device *dev) |
| 232 | { |
| 233 | struct drm_i915_private *dev_priv = dev->dev_private; |
| 234 | uint32_t ctx_size; |
| 235 | |
| 236 | if (!HAS_HW_CONTEXTS(dev)) |
| 237 | return; |
| 238 | |
| 239 | /* If called from reset, or thaw... we've been here already */ |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 240 | if (dev_priv->hw_contexts_disabled || |
| 241 | dev_priv->ring[RCS].default_context) |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 242 | return; |
| 243 | |
| 244 | ctx_size = get_context_size(dev); |
| 245 | dev_priv->hw_context_size = get_context_size(dev); |
| 246 | dev_priv->hw_context_size = round_up(dev_priv->hw_context_size, 4096); |
| 247 | |
| 248 | if (ctx_size <= 0 || ctx_size > (1<<20)) { |
| 249 | dev_priv->hw_contexts_disabled = true; |
| 250 | return; |
| 251 | } |
| 252 | |
| 253 | if (create_default_context(dev_priv)) { |
| 254 | dev_priv->hw_contexts_disabled = true; |
| 255 | return; |
| 256 | } |
| 257 | |
| 258 | DRM_DEBUG_DRIVER("HW context support initialized\n"); |
| 259 | } |
| 260 | |
| 261 | void i915_gem_context_fini(struct drm_device *dev) |
| 262 | { |
| 263 | struct drm_i915_private *dev_priv = dev->dev_private; |
| 264 | |
| 265 | if (dev_priv->hw_contexts_disabled) |
| 266 | return; |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 267 | |
| 268 | i915_gem_object_unpin(dev_priv->ring[RCS].default_context->obj); |
| 269 | |
| 270 | do_destroy(dev_priv->ring[RCS].default_context); |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 271 | } |
| 272 | |
| 273 | void i915_gem_context_open(struct drm_device *dev, struct drm_file *file) |
| 274 | { |
| 275 | struct drm_i915_private *dev_priv = dev->dev_private; |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 276 | struct drm_i915_file_private *file_priv = file->driver_priv; |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 277 | |
| 278 | if (dev_priv->hw_contexts_disabled) |
| 279 | return; |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 280 | |
| 281 | idr_init(&file_priv->context_idr); |
| 282 | } |
| 283 | |
| 284 | static int context_idr_cleanup(int id, void *p, void *data) |
| 285 | { |
| 286 | struct drm_file *file = (struct drm_file *)data; |
| 287 | struct drm_i915_file_private *file_priv = file->driver_priv; |
| 288 | struct i915_hw_context *ctx; |
| 289 | |
| 290 | BUG_ON(id == DEFAULT_CONTEXT_ID); |
| 291 | ctx = i915_gem_context_get(file_priv, id); |
| 292 | if (WARN_ON(ctx == NULL)) |
| 293 | return -ENXIO; |
| 294 | |
| 295 | do_destroy(ctx); |
| 296 | |
| 297 | return 0; |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 298 | } |
| 299 | |
| 300 | void i915_gem_context_close(struct drm_device *dev, struct drm_file *file) |
| 301 | { |
| 302 | struct drm_i915_private *dev_priv = dev->dev_private; |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 303 | struct drm_i915_file_private *file_priv = file->driver_priv; |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 304 | |
| 305 | if (dev_priv->hw_contexts_disabled) |
| 306 | return; |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 307 | |
| 308 | mutex_lock(&dev->struct_mutex); |
| 309 | idr_for_each(&file_priv->context_idr, context_idr_cleanup, file); |
| 310 | idr_destroy(&file_priv->context_idr); |
| 311 | mutex_unlock(&dev->struct_mutex); |
| 312 | } |
| 313 | |
Ben Widawsky | e055684 | 2012-06-04 14:42:46 -0700 | [diff] [blame] | 314 | static struct i915_hw_context * |
Ben Widawsky | 4052105 | 2012-06-04 14:42:43 -0700 | [diff] [blame] | 315 | i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id) |
| 316 | { |
| 317 | return (struct i915_hw_context *)idr_find(&file_priv->context_idr, id); |
Ben Widawsky | 254f965 | 2012-06-04 14:42:42 -0700 | [diff] [blame] | 318 | } |
Ben Widawsky | e055684 | 2012-06-04 14:42:46 -0700 | [diff] [blame] | 319 | |
| 320 | static inline int |
| 321 | mi_set_context(struct intel_ring_buffer *ring, |
| 322 | struct i915_hw_context *new_context, |
| 323 | u32 hw_flags) |
| 324 | { |
| 325 | int ret; |
| 326 | |
Ben Widawsky | e37ec39 | 2012-06-04 14:42:48 -0700 | [diff] [blame^] | 327 | ret = intel_ring_begin(ring, 6); |
Ben Widawsky | e055684 | 2012-06-04 14:42:46 -0700 | [diff] [blame] | 328 | if (ret) |
| 329 | return ret; |
| 330 | |
Ben Widawsky | e37ec39 | 2012-06-04 14:42:48 -0700 | [diff] [blame^] | 331 | if (IS_GEN7(ring->dev)) |
| 332 | intel_ring_emit(ring, MI_ARB_ON_OFF | MI_ARB_DISABLE); |
| 333 | else |
| 334 | intel_ring_emit(ring, MI_NOOP); |
| 335 | |
Ben Widawsky | e055684 | 2012-06-04 14:42:46 -0700 | [diff] [blame] | 336 | intel_ring_emit(ring, MI_NOOP); |
| 337 | intel_ring_emit(ring, MI_SET_CONTEXT); |
| 338 | intel_ring_emit(ring, new_context->obj->gtt_offset | |
| 339 | MI_MM_SPACE_GTT | |
| 340 | MI_SAVE_EXT_STATE_EN | |
| 341 | MI_RESTORE_EXT_STATE_EN | |
| 342 | hw_flags); |
| 343 | /* w/a: MI_SET_CONTEXT must always be followed by MI_NOOP */ |
| 344 | intel_ring_emit(ring, MI_NOOP); |
| 345 | |
Ben Widawsky | e37ec39 | 2012-06-04 14:42:48 -0700 | [diff] [blame^] | 346 | if (IS_GEN7(ring->dev)) |
| 347 | intel_ring_emit(ring, MI_ARB_ON_OFF | MI_ARB_ENABLE); |
| 348 | else |
| 349 | intel_ring_emit(ring, MI_NOOP); |
| 350 | |
Ben Widawsky | e055684 | 2012-06-04 14:42:46 -0700 | [diff] [blame] | 351 | intel_ring_advance(ring); |
| 352 | |
| 353 | return ret; |
| 354 | } |
| 355 | |
| 356 | static int do_switch(struct drm_i915_gem_object *from_obj, |
| 357 | struct i915_hw_context *to, |
| 358 | u32 seqno) |
| 359 | { |
| 360 | struct intel_ring_buffer *ring = NULL; |
| 361 | u32 hw_flags = 0; |
| 362 | int ret; |
| 363 | |
| 364 | BUG_ON(to == NULL); |
| 365 | BUG_ON(from_obj != NULL && from_obj->pin_count == 0); |
| 366 | |
| 367 | ret = i915_gem_object_pin(to->obj, CONTEXT_ALIGN, false); |
| 368 | if (ret) |
| 369 | return ret; |
| 370 | |
Daniel Vetter | 3af7b85 | 2012-06-14 00:08:32 +0200 | [diff] [blame] | 371 | if (!to->obj->has_global_gtt_mapping) |
| 372 | i915_gem_gtt_bind_object(to->obj, to->obj->cache_level); |
| 373 | |
Ben Widawsky | e055684 | 2012-06-04 14:42:46 -0700 | [diff] [blame] | 374 | if (!to->is_initialized || is_default_context(to)) |
| 375 | hw_flags |= MI_RESTORE_INHIBIT; |
| 376 | else if (WARN_ON_ONCE(from_obj == to->obj)) /* not yet expected */ |
| 377 | hw_flags |= MI_FORCE_RESTORE; |
| 378 | |
| 379 | ring = to->ring; |
| 380 | ret = mi_set_context(ring, to, hw_flags); |
| 381 | if (ret) { |
| 382 | i915_gem_object_unpin(to->obj); |
| 383 | return ret; |
| 384 | } |
| 385 | |
| 386 | /* The backing object for the context is done after switching to the |
| 387 | * *next* context. Therefore we cannot retire the previous context until |
| 388 | * the next context has already started running. In fact, the below code |
| 389 | * is a bit suboptimal because the retiring can occur simply after the |
| 390 | * MI_SET_CONTEXT instead of when the next seqno has completed. |
| 391 | */ |
| 392 | if (from_obj != NULL) { |
| 393 | from_obj->base.read_domains = I915_GEM_DOMAIN_INSTRUCTION; |
| 394 | i915_gem_object_move_to_active(from_obj, ring, seqno); |
| 395 | /* As long as MI_SET_CONTEXT is serializing, ie. it flushes the |
| 396 | * whole damn pipeline, we don't need to explicitly mark the |
| 397 | * object dirty. The only exception is that the context must be |
| 398 | * correct in case the object gets swapped out. Ideally we'd be |
| 399 | * able to defer doing this until we know the object would be |
| 400 | * swapped, but there is no way to do that yet. |
| 401 | */ |
| 402 | from_obj->dirty = 1; |
| 403 | BUG_ON(from_obj->ring != to->ring); |
| 404 | i915_gem_object_unpin(from_obj); |
| 405 | } |
| 406 | |
| 407 | ring->last_context_obj = to->obj; |
| 408 | to->is_initialized = true; |
| 409 | |
| 410 | return 0; |
| 411 | } |
| 412 | |
| 413 | /** |
| 414 | * i915_switch_context() - perform a GPU context switch. |
| 415 | * @ring: ring for which we'll execute the context switch |
| 416 | * @file_priv: file_priv associated with the context, may be NULL |
| 417 | * @id: context id number |
| 418 | * @seqno: sequence number by which the new context will be switched to |
| 419 | * @flags: |
| 420 | * |
| 421 | * The context life cycle is simple. The context refcount is incremented and |
| 422 | * decremented by 1 and create and destroy. If the context is in use by the GPU, |
| 423 | * it will have a refoucnt > 1. This allows us to destroy the context abstract |
| 424 | * object while letting the normal object tracking destroy the backing BO. |
| 425 | */ |
| 426 | int i915_switch_context(struct intel_ring_buffer *ring, |
| 427 | struct drm_file *file, |
| 428 | int to_id) |
| 429 | { |
| 430 | struct drm_i915_private *dev_priv = ring->dev->dev_private; |
| 431 | struct drm_i915_file_private *file_priv = NULL; |
| 432 | struct i915_hw_context *to; |
| 433 | struct drm_i915_gem_object *from_obj = ring->last_context_obj; |
| 434 | int ret; |
| 435 | |
| 436 | if (dev_priv->hw_contexts_disabled) |
| 437 | return 0; |
| 438 | |
| 439 | if (ring != &dev_priv->ring[RCS]) |
| 440 | return 0; |
| 441 | |
| 442 | if (file) |
| 443 | file_priv = file->driver_priv; |
| 444 | |
| 445 | if (to_id == DEFAULT_CONTEXT_ID) { |
| 446 | to = ring->default_context; |
| 447 | } else { |
| 448 | to = i915_gem_context_get(file_priv, to_id); |
| 449 | if (to == NULL) |
| 450 | return -EINVAL; |
| 451 | } |
| 452 | |
| 453 | if (from_obj == to->obj) |
| 454 | return 0; |
| 455 | |
| 456 | ret = do_switch(from_obj, to, i915_gem_next_request_seqno(to->ring)); |
| 457 | if (ret) |
| 458 | return ret; |
| 459 | |
| 460 | /* Just to make the code a little cleaner we take the object reference |
| 461 | * after the switch was successful. It would be more intuitive to ref |
| 462 | * the 'to' object before the switch but we know the refcount must be >0 |
| 463 | * if context_get() succeeded, and we hold struct mutex. So it's safe to |
| 464 | * do this here/now |
| 465 | */ |
| 466 | drm_gem_object_reference(&to->obj->base); |
| 467 | if (from_obj != NULL) |
| 468 | drm_gem_object_unreference(&from_obj->base); |
| 469 | return ret; |
| 470 | } |