git.oblomov.eu Git - linux-2.6/blob - drivers/gpu/drm/i915/i915_irq.c

   1 /* i915_irq.c -- IRQ support for the I915 -*- linux-c -*-
   2  */
   3 /*
   4  * Copyright 2003 Tungsten Graphics, Inc., Cedar Park, Texas.
   5  * All Rights Reserved.
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a
   8  * copy of this software and associated documentation files (the
   9  * "Software"), to deal in the Software without restriction, including
  10  * without limitation the rights to use, copy, modify, merge, publish,
  11  * distribute, sub license, and/or sell copies of the Software, and to
  12  * permit persons to whom the Software is furnished to do so, subject to
  13  * the following conditions:
  14  *
  15  * The above copyright notice and this permission notice (including the
  16  * next paragraph) shall be included in all copies or substantial portions
  17  * of the Software.
  18  *
  19  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  20  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  21  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  22  * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS BE LIABLE FOR
  23  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  24  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  25  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  26  *
  27  */
  28
  29 #include "drmP.h"
  30 #include "drm.h"
  31 #include "i915_drm.h"
  32 #include "i915_drv.h"
  33 #include "intel_drv.h"
  34
  35 #define MAX_NOPID ((u32)~0)
  36
  37 /**
  38  * Interrupts that are always left unmasked.
  39  *
  40  * Since pipe events are edge-triggered from the PIPESTAT register to IIR,
  41  * we leave them always unmasked in IMR and then control enabling them through
  42  * PIPESTAT alone.
  43  */
  44 #define I915_INTERRUPT_ENABLE_FIX (I915_ASLE_INTERRUPT | \
  45                                    I915_DISPLAY_PIPE_A_EVENT_INTERRUPT |  \
  46                                    I915_DISPLAY_PIPE_B_EVENT_INTERRUPT)
  47
  48 /** Interrupts that we mask and unmask at runtime. */
  49 #define I915_INTERRUPT_ENABLE_VAR (I915_USER_INTERRUPT)
  50
  51 /** These are all of the interrupts used by the driver */
  52 #define I915_INTERRUPT_ENABLE_MASK (I915_INTERRUPT_ENABLE_FIX | \
  53                                     I915_INTERRUPT_ENABLE_VAR)
  54
  55 #define I915_PIPE_VBLANK_STATUS (PIPE_START_VBLANK_INTERRUPT_STATUS |\
  56                                  PIPE_VBLANK_INTERRUPT_STATUS)
  57
  58 #define I915_PIPE_VBLANK_ENABLE (PIPE_START_VBLANK_INTERRUPT_ENABLE |\
  59                                  PIPE_VBLANK_INTERRUPT_ENABLE)
  60
  61 #define DRM_I915_VBLANK_PIPE_ALL        (DRM_I915_VBLANK_PIPE_A | \
  62                                          DRM_I915_VBLANK_PIPE_B)
  63
  64 void
  65 i915_enable_irq(drm_i915_private_t *dev_priv, u32 mask)
  66 {
  67         if ((dev_priv->irq_mask_reg & mask) != 0) {
  68                 dev_priv->irq_mask_reg &= ~mask;
  69                 I915_WRITE(IMR, dev_priv->irq_mask_reg);
  70                 (void) I915_READ(IMR);
  71         }
  72 }
  73
  74 static inline void
  75 i915_disable_irq(drm_i915_private_t *dev_priv, u32 mask)
  76 {
  77         if ((dev_priv->irq_mask_reg & mask) != mask) {
  78                 dev_priv->irq_mask_reg |= mask;
  79                 I915_WRITE(IMR, dev_priv->irq_mask_reg);
  80                 (void) I915_READ(IMR);
  81         }
  82 }
  83
  84 static inline u32
  85 i915_pipestat(int pipe)
  86 {
  87         if (pipe == 0)
  88                 return PIPEASTAT;
  89         if (pipe == 1)
  90                 return PIPEBSTAT;
  91         BUG();
  92 }
  93
  94 void
  95 i915_enable_pipestat(drm_i915_private_t *dev_priv, int pipe, u32 mask)
  96 {
  97         if ((dev_priv->pipestat[pipe] & mask) != mask) {
  98                 u32 reg = i915_pipestat(pipe);
  99
 100                 dev_priv->pipestat[pipe] |= mask;
 101                 /* Enable the interrupt, clear any pending status */
 102                 I915_WRITE(reg, dev_priv->pipestat[pipe] | (mask >> 16));
 103                 (void) I915_READ(reg);
 104         }
 105 }
 106
 107 void
 108 i915_disable_pipestat(drm_i915_private_t *dev_priv, int pipe, u32 mask)
 109 {
 110         if ((dev_priv->pipestat[pipe] & mask) != 0) {
 111                 u32 reg = i915_pipestat(pipe);
 112
 113                 dev_priv->pipestat[pipe] &= ~mask;
 114                 I915_WRITE(reg, dev_priv->pipestat[pipe]);
 115                 (void) I915_READ(reg);
 116         }
 117 }
 118
 119 /**
 120  * i915_pipe_enabled - check if a pipe is enabled
 121  * @dev: DRM device
 122  * @pipe: pipe to check
 123  *
 124  * Reading certain registers when the pipe is disabled can hang the chip.
 125  * Use this routine to make sure the PLL is running and the pipe is active
 126  * before reading such registers if unsure.
 127  */
 128 static int
 129 i915_pipe_enabled(struct drm_device *dev, int pipe)
 130 {
 131         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 132         unsigned long pipeconf = pipe ? PIPEBCONF : PIPEACONF;
 133
 134         if (I915_READ(pipeconf) & PIPEACONF_ENABLE)
 135                 return 1;
 136
 137         return 0;
 138 }
 139
 140 /* Called from drm generic code, passed a 'crtc', which
 141  * we use as a pipe index
 142  */
 143 u32 i915_get_vblank_counter(struct drm_device *dev, int pipe)
 144 {
 145         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 146         unsigned long high_frame;
 147         unsigned long low_frame;
 148         u32 high1, high2, low, count;
 149
 150         high_frame = pipe ? PIPEBFRAMEHIGH : PIPEAFRAMEHIGH;
 151         low_frame = pipe ? PIPEBFRAMEPIXEL : PIPEAFRAMEPIXEL;
 152
 153         if (!i915_pipe_enabled(dev, pipe)) {
 154                 DRM_ERROR("trying to get vblank count for disabled pipe %d\n", pipe);
 155                 return 0;
 156         }
 157
 158         /*
 159          * High & low register fields aren't synchronized, so make sure
 160          * we get a low value that's stable across two reads of the high
 161          * register.
 162          */
 163         do {
 164                 high1 = ((I915_READ(high_frame) & PIPE_FRAME_HIGH_MASK) >>
 165                          PIPE_FRAME_HIGH_SHIFT);
 166                 low =  ((I915_READ(low_frame) & PIPE_FRAME_LOW_MASK) >>
 167                         PIPE_FRAME_LOW_SHIFT);
 168                 high2 = ((I915_READ(high_frame) & PIPE_FRAME_HIGH_MASK) >>
 169                          PIPE_FRAME_HIGH_SHIFT);
 170         } while (high1 != high2);
 171
 172         count = (high1 << 8) | low;
 173
 174         return count;
 175 }
 176
 177 u32 gm45_get_vblank_counter(struct drm_device *dev, int pipe)
 178 {
 179         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 180         int reg = pipe ? PIPEB_FRMCOUNT_GM45 : PIPEA_FRMCOUNT_GM45;
 181
 182         if (!i915_pipe_enabled(dev, pipe)) {
 183                 DRM_ERROR("trying to get vblank count for disabled pipe %d\n", pipe);
 184                 return 0;
 185         }
 186
 187         return I915_READ(reg);
 188 }
 189
 190 irqreturn_t i915_driver_irq_handler(DRM_IRQ_ARGS)
 191 {
 192         struct drm_device *dev = (struct drm_device *) arg;
 193         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 194         struct drm_i915_master_private *master_priv;
 195         u32 iir, new_iir;
 196         u32 pipea_stats, pipeb_stats;
 197         u32 vblank_status;
 198         u32 vblank_enable;
 199         int vblank = 0;
 200         unsigned long irqflags;
 201         int irq_received;
 202         int ret = IRQ_NONE;
 203
 204         atomic_inc(&dev_priv->irq_received);
 205
 206         iir = I915_READ(IIR);
 207
 208         if (IS_I965G(dev)) {
 209                 vblank_status = I915_START_VBLANK_INTERRUPT_STATUS;
 210                 vblank_enable = PIPE_START_VBLANK_INTERRUPT_ENABLE;
 211         } else {
 212                 vblank_status = I915_VBLANK_INTERRUPT_STATUS;
 213                 vblank_enable = I915_VBLANK_INTERRUPT_ENABLE;
 214         }
 215
 216         for (;;) {
 217                 irq_received = iir != 0;
 218
 219                 /* Can't rely on pipestat interrupt bit in iir as it might
 220                  * have been cleared after the pipestat interrupt was received.
 221                  * It doesn't set the bit in iir again, but it still produces
 222                  * interrupts (for non-MSI).
 223                  */
 224                 spin_lock_irqsave(&dev_priv->user_irq_lock, irqflags);
 225                 pipea_stats = I915_READ(PIPEASTAT);
 226                 pipeb_stats = I915_READ(PIPEBSTAT);
 227
 228                 /*
 229                  * Clear the PIPE(A|B)STAT regs before the IIR
 230                  */
 231                 if (pipea_stats & 0x8000ffff) {
 232                         I915_WRITE(PIPEASTAT, pipea_stats);
 233                         irq_received = 1;
 234                 }
 235
 236                 if (pipeb_stats & 0x8000ffff) {
 237                         I915_WRITE(PIPEBSTAT, pipeb_stats);
 238                         irq_received = 1;
 239                 }
 240                 spin_unlock_irqrestore(&dev_priv->user_irq_lock, irqflags);
 241
 242                 if (!irq_received)
 243                         break;
 244
 245                 ret = IRQ_HANDLED;
 246
 247                 I915_WRITE(IIR, iir);
 248                 new_iir = I915_READ(IIR); /* Flush posted writes */
 249
 250                 if (dev->primary->master) {
 251                         master_priv = dev->primary->master->driver_priv;
 252                         if (master_priv->sarea_priv)
 253                                 master_priv->sarea_priv->last_dispatch =
 254                                         READ_BREADCRUMB(dev_priv);
 255                 }
 256
 257                 if (iir & I915_USER_INTERRUPT) {
 258                         dev_priv->mm.irq_gem_seqno = i915_get_gem_seqno(dev);
 259                         DRM_WAKEUP(&dev_priv->irq_queue);
 260                 }
 261
 262                 if (pipea_stats & vblank_status) {
 263                         vblank++;
 264                         drm_handle_vblank(dev, 0);
 265                 }
 266
 267                 if (pipeb_stats & vblank_status) {
 268                         vblank++;
 269                         drm_handle_vblank(dev, 1);
 270                 }
 271
 272                 if ((pipeb_stats & I915_LEGACY_BLC_EVENT_STATUS) ||
 273                     (iir & I915_ASLE_INTERRUPT))
 274                         opregion_asle_intr(dev);
 275
 276                 /* With MSI, interrupts are only generated when iir
 277                  * transitions from zero to nonzero.  If another bit got
 278                  * set while we were handling the existing iir bits, then
 279                  * we would never get another interrupt.
 280                  *
 281                  * This is fine on non-MSI as well, as if we hit this path
 282                  * we avoid exiting the interrupt handler only to generate
 283                  * another one.
 284                  *
 285                  * Note that for MSI this could cause a stray interrupt report
 286                  * if an interrupt landed in the time between writing IIR and
 287                  * the posting read.  This should be rare enough to never
 288                  * trigger the 99% of 100,000 interrupts test for disabling
 289                  * stray interrupts.
 290                  */
 291                 iir = new_iir;
 292         }
 293
 294         return ret;
 295 }
 296
 297 static int i915_emit_irq(struct drm_device * dev)
 298 {
 299         drm_i915_private_t *dev_priv = dev->dev_private;
 300         struct drm_i915_master_private *master_priv = dev->primary->master->driver_priv;
 301         RING_LOCALS;
 302
 303         i915_kernel_lost_context(dev);
 304
 305         DRM_DEBUG("\n");
 306
 307         dev_priv->counter++;
 308         if (dev_priv->counter > 0x7FFFFFFFUL)
 309                 dev_priv->counter = 1;
 310         if (master_priv->sarea_priv)
 311                 master_priv->sarea_priv->last_enqueue = dev_priv->counter;
 312
 313         BEGIN_LP_RING(4);
 314         OUT_RING(MI_STORE_DWORD_INDEX);
 315         OUT_RING(I915_BREADCRUMB_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
 316         OUT_RING(dev_priv->counter);
 317         OUT_RING(MI_USER_INTERRUPT);
 318         ADVANCE_LP_RING();
 319
 320         return dev_priv->counter;
 321 }
 322
 323 void i915_user_irq_get(struct drm_device *dev)
 324 {
 325         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 326         unsigned long irqflags;
 327
 328         spin_lock_irqsave(&dev_priv->user_irq_lock, irqflags);
 329         if (dev->irq_enabled && (++dev_priv->user_irq_refcount == 1))
 330                 i915_enable_irq(dev_priv, I915_USER_INTERRUPT);
 331         spin_unlock_irqrestore(&dev_priv->user_irq_lock, irqflags);
 332 }
 333
 334 void i915_user_irq_put(struct drm_device *dev)
 335 {
 336         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 337         unsigned long irqflags;
 338
 339         spin_lock_irqsave(&dev_priv->user_irq_lock, irqflags);
 340         BUG_ON(dev->irq_enabled && dev_priv->user_irq_refcount <= 0);
 341         if (dev->irq_enabled && (--dev_priv->user_irq_refcount == 0))
 342                 i915_disable_irq(dev_priv, I915_USER_INTERRUPT);
 343         spin_unlock_irqrestore(&dev_priv->user_irq_lock, irqflags);
 344 }
 345
 346 static int i915_wait_irq(struct drm_device * dev, int irq_nr)
 347 {
 348         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 349         struct drm_i915_master_private *master_priv = dev->primary->master->driver_priv;
 350         int ret = 0;
 351
 352         DRM_DEBUG("irq_nr=%d breadcrumb=%d\n", irq_nr,
 353                   READ_BREADCRUMB(dev_priv));
 354
 355         if (READ_BREADCRUMB(dev_priv) >= irq_nr) {
 356                 if (master_priv->sarea_priv)
 357                         master_priv->sarea_priv->last_dispatch = READ_BREADCRUMB(dev_priv);
 358                 return 0;
 359         }
 360
 361         if (master_priv->sarea_priv)
 362                 master_priv->sarea_priv->perf_boxes |= I915_BOX_WAIT;
 363
 364         i915_user_irq_get(dev);
 365         DRM_WAIT_ON(ret, dev_priv->irq_queue, 3 * DRM_HZ,
 366                     READ_BREADCRUMB(dev_priv) >= irq_nr);
 367         i915_user_irq_put(dev);
 368
 369         if (ret == -EBUSY) {
 370                 DRM_ERROR("EBUSY -- rec: %d emitted: %d\n",
 371                           READ_BREADCRUMB(dev_priv), (int)dev_priv->counter);
 372         }
 373
 374         return ret;
 375 }
 376
 377 /* Needs the lock as it touches the ring.
 378  */
 379 int i915_irq_emit(struct drm_device *dev, void *data,
 380                          struct drm_file *file_priv)
 381 {
 382         drm_i915_private_t *dev_priv = dev->dev_private;
 383         drm_i915_irq_emit_t *emit = data;
 384         int result;
 385
 386         RING_LOCK_TEST_WITH_RETURN(dev, file_priv);
 387
 388         if (!dev_priv) {
 389                 DRM_ERROR("called with no initialization\n");
 390                 return -EINVAL;
 391         }
 392         mutex_lock(&dev->struct_mutex);
 393         result = i915_emit_irq(dev);
 394         mutex_unlock(&dev->struct_mutex);
 395
 396         if (DRM_COPY_TO_USER(emit->irq_seq, &result, sizeof(int))) {
 397                 DRM_ERROR("copy_to_user\n");
 398                 return -EFAULT;
 399         }
 400
 401         return 0;
 402 }
 403
 404 /* Doesn't need the hardware lock.
 405  */
 406 int i915_irq_wait(struct drm_device *dev, void *data,
 407                          struct drm_file *file_priv)
 408 {
 409         drm_i915_private_t *dev_priv = dev->dev_private;
 410         drm_i915_irq_wait_t *irqwait = data;
 411
 412         if (!dev_priv) {
 413                 DRM_ERROR("called with no initialization\n");
 414                 return -EINVAL;
 415         }
 416
 417         return i915_wait_irq(dev, irqwait->irq_seq);
 418 }
 419
 420 /* Called from drm generic code, passed 'crtc' which
 421  * we use as a pipe index
 422  */
 423 int i915_enable_vblank(struct drm_device *dev, int pipe)
 424 {
 425         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 426         unsigned long irqflags;
 427         int pipeconf_reg = (pipe == 0) ? PIPEACONF : PIPEBCONF;
 428         u32 pipeconf;
 429
 430         pipeconf = I915_READ(pipeconf_reg);
 431         if (!(pipeconf & PIPEACONF_ENABLE))
 432                 return -EINVAL;
 433
 434         spin_lock_irqsave(&dev_priv->user_irq_lock, irqflags);
 435         if (IS_I965G(dev))
 436                 i915_enable_pipestat(dev_priv, pipe,
 437                                      PIPE_START_VBLANK_INTERRUPT_ENABLE);
 438         else
 439                 i915_enable_pipestat(dev_priv, pipe,
 440                                      PIPE_VBLANK_INTERRUPT_ENABLE);
 441         spin_unlock_irqrestore(&dev_priv->user_irq_lock, irqflags);
 442         return 0;
 443 }
 444
 445 /* Called from drm generic code, passed 'crtc' which
 446  * we use as a pipe index
 447  */
 448 void i915_disable_vblank(struct drm_device *dev, int pipe)
 449 {
 450         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 451         unsigned long irqflags;
 452
 453         spin_lock_irqsave(&dev_priv->user_irq_lock, irqflags);
 454         i915_disable_pipestat(dev_priv, pipe,
 455                               PIPE_VBLANK_INTERRUPT_ENABLE |
 456                               PIPE_START_VBLANK_INTERRUPT_ENABLE);
 457         spin_unlock_irqrestore(&dev_priv->user_irq_lock, irqflags);
 458 }
 459
 460 void i915_enable_interrupt (struct drm_device *dev)
 461 {
 462         struct drm_i915_private *dev_priv = dev->dev_private;
 463         opregion_enable_asle(dev);
 464         dev_priv->irq_enabled = 1;
 465 }
 466
 467
 468 /* Set the vblank monitor pipe
 469  */
 470 int i915_vblank_pipe_set(struct drm_device *dev, void *data,
 471                          struct drm_file *file_priv)
 472 {
 473         drm_i915_private_t *dev_priv = dev->dev_private;
 474
 475         if (!dev_priv) {
 476                 DRM_ERROR("called with no initialization\n");
 477                 return -EINVAL;
 478         }
 479
 480         return 0;
 481 }
 482
 483 int i915_vblank_pipe_get(struct drm_device *dev, void *data,
 484                          struct drm_file *file_priv)
 485 {
 486         drm_i915_private_t *dev_priv = dev->dev_private;
 487         drm_i915_vblank_pipe_t *pipe = data;
 488
 489         if (!dev_priv) {
 490                 DRM_ERROR("called with no initialization\n");
 491                 return -EINVAL;
 492         }
 493
 494         pipe->pipe = DRM_I915_VBLANK_PIPE_A | DRM_I915_VBLANK_PIPE_B;
 495
 496         return 0;
 497 }
 498
 499 /**
 500  * Schedule buffer swap at given vertical blank.
 501  */
 502 int i915_vblank_swap(struct drm_device *dev, void *data,
 503                      struct drm_file *file_priv)
 504 {
 505         /* The delayed swap mechanism was fundamentally racy, and has been
 506          * removed.  The model was that the client requested a delayed flip/swap
 507          * from the kernel, then waited for vblank before continuing to perform
 508          * rendering.  The problem was that the kernel might wake the client
 509          * up before it dispatched the vblank swap (since the lock has to be
 510          * held while touching the ringbuffer), in which case the client would
 511          * clear and start the next frame before the swap occurred, and
 512          * flicker would occur in addition to likely missing the vblank.
 513          *
 514          * In the absence of this ioctl, userland falls back to a correct path
 515          * of waiting for a vblank, then dispatching the swap on its own.
 516          * Context switching to userland and back is plenty fast enough for
 517          * meeting the requirements of vblank swapping.
 518          */
 519         return -EINVAL;
 520 }
 521
 522 /* drm_dma.h hooks
 523 */
 524 void i915_driver_irq_preinstall(struct drm_device * dev)
 525 {
 526         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 527
 528         atomic_set(&dev_priv->irq_received, 0);
 529
 530         I915_WRITE(HWSTAM, 0xeffe);
 531         I915_WRITE(PIPEASTAT, 0);
 532         I915_WRITE(PIPEBSTAT, 0);
 533         I915_WRITE(IMR, 0xffffffff);
 534         I915_WRITE(IER, 0x0);
 535         (void) I915_READ(IER);
 536 }
 537
 538 int i915_driver_irq_postinstall(struct drm_device *dev)
 539 {
 540         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 541
 542         dev_priv->vblank_pipe = DRM_I915_VBLANK_PIPE_A | DRM_I915_VBLANK_PIPE_B;
 543
 544         dev->max_vblank_count = 0xffffff; /* only 24 bits of frame count */
 545
 546         /* Unmask the interrupts that we always want on. */
 547         dev_priv->irq_mask_reg = ~I915_INTERRUPT_ENABLE_FIX;
 548
 549         dev_priv->pipestat[0] = 0;
 550         dev_priv->pipestat[1] = 0;
 551
 552         /* Disable pipe interrupt enables, clear pending pipe status */
 553         I915_WRITE(PIPEASTAT, I915_READ(PIPEASTAT) & 0x8000ffff);
 554         I915_WRITE(PIPEBSTAT, I915_READ(PIPEBSTAT) & 0x8000ffff);
 555         /* Clear pending interrupt status */
 556         I915_WRITE(IIR, I915_READ(IIR));
 557
 558         I915_WRITE(IER, I915_INTERRUPT_ENABLE_MASK);
 559         I915_WRITE(IMR, dev_priv->irq_mask_reg);
 560         (void) I915_READ(IER);
 561
 562         opregion_enable_asle(dev);
 563         DRM_INIT_WAITQUEUE(&dev_priv->irq_queue);
 564
 565         return 0;
 566 }
 567
 568 void i915_driver_irq_uninstall(struct drm_device * dev)
 569 {
 570         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 571
 572         if (!dev_priv)
 573                 return;
 574
 575         dev_priv->vblank_pipe = 0;
 576
 577         I915_WRITE(HWSTAM, 0xffffffff);
 578         I915_WRITE(PIPEASTAT, 0);
 579         I915_WRITE(PIPEBSTAT, 0);
 580         I915_WRITE(IMR, 0xffffffff);
 581         I915_WRITE(IER, 0x0);
 582
 583         I915_WRITE(PIPEASTAT, I915_READ(PIPEASTAT) & 0x8000ffff);
 584         I915_WRITE(PIPEBSTAT, I915_READ(PIPEBSTAT) & 0x8000ffff);
 585         I915_WRITE(IIR, I915_READ(IIR));
 586 }