Merge branch 'upstream-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jgarzi...
[linux-2.6] / 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
34 #define USER_INT_FLAG (1<<1)
35 #define VSYNC_PIPEB_FLAG (1<<5)
36 #define VSYNC_PIPEA_FLAG (1<<7)
37
38 #define MAX_NOPID ((u32)~0)
39
40 /**
41  * Emit blits for scheduled buffer swaps.
42  *
43  * This function will be called with the HW lock held.
44  */
45 static void i915_vblank_tasklet(struct drm_device *dev)
46 {
47         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
48         unsigned long irqflags;
49         struct list_head *list, *tmp, hits, *hit;
50         int nhits, nrects, slice[2], upper[2], lower[2], i;
51         unsigned counter[2] = { atomic_read(&dev->vbl_received),
52                                 atomic_read(&dev->vbl_received2) };
53         struct drm_drawable_info *drw;
54         drm_i915_sarea_t *sarea_priv = dev_priv->sarea_priv;
55         u32 cpp = dev_priv->cpp;
56         u32 cmd = (cpp == 4) ? (XY_SRC_COPY_BLT_CMD |
57                                 XY_SRC_COPY_BLT_WRITE_ALPHA |
58                                 XY_SRC_COPY_BLT_WRITE_RGB)
59                              : XY_SRC_COPY_BLT_CMD;
60         u32 src_pitch = sarea_priv->pitch * cpp;
61         u32 dst_pitch = sarea_priv->pitch * cpp;
62         u32 ropcpp = (0xcc << 16) | ((cpp - 1) << 24);
63         RING_LOCALS;
64
65         if (IS_I965G(dev) && sarea_priv->front_tiled) {
66                 cmd |= XY_SRC_COPY_BLT_DST_TILED;
67                 dst_pitch >>= 2;
68         }
69         if (IS_I965G(dev) && sarea_priv->back_tiled) {
70                 cmd |= XY_SRC_COPY_BLT_SRC_TILED;
71                 src_pitch >>= 2;
72         }
73
74         DRM_DEBUG("\n");
75
76         INIT_LIST_HEAD(&hits);
77
78         nhits = nrects = 0;
79
80         spin_lock_irqsave(&dev_priv->swaps_lock, irqflags);
81
82         /* Find buffer swaps scheduled for this vertical blank */
83         list_for_each_safe(list, tmp, &dev_priv->vbl_swaps.head) {
84                 drm_i915_vbl_swap_t *vbl_swap =
85                         list_entry(list, drm_i915_vbl_swap_t, head);
86
87                 if ((counter[vbl_swap->pipe] - vbl_swap->sequence) > (1<<23))
88                         continue;
89
90                 list_del(list);
91                 dev_priv->swaps_pending--;
92
93                 spin_unlock(&dev_priv->swaps_lock);
94                 spin_lock(&dev->drw_lock);
95
96                 drw = drm_get_drawable_info(dev, vbl_swap->drw_id);
97
98                 if (!drw) {
99                         spin_unlock(&dev->drw_lock);
100                         drm_free(vbl_swap, sizeof(*vbl_swap), DRM_MEM_DRIVER);
101                         spin_lock(&dev_priv->swaps_lock);
102                         continue;
103                 }
104
105                 list_for_each(hit, &hits) {
106                         drm_i915_vbl_swap_t *swap_cmp =
107                                 list_entry(hit, drm_i915_vbl_swap_t, head);
108                         struct drm_drawable_info *drw_cmp =
109                                 drm_get_drawable_info(dev, swap_cmp->drw_id);
110
111                         if (drw_cmp &&
112                             drw_cmp->rects[0].y1 > drw->rects[0].y1) {
113                                 list_add_tail(list, hit);
114                                 break;
115                         }
116                 }
117
118                 spin_unlock(&dev->drw_lock);
119
120                 /* List of hits was empty, or we reached the end of it */
121                 if (hit == &hits)
122                         list_add_tail(list, hits.prev);
123
124                 nhits++;
125
126                 spin_lock(&dev_priv->swaps_lock);
127         }
128
129         if (nhits == 0) {
130                 spin_unlock_irqrestore(&dev_priv->swaps_lock, irqflags);
131                 return;
132         }
133
134         spin_unlock(&dev_priv->swaps_lock);
135
136         i915_kernel_lost_context(dev);
137
138         if (IS_I965G(dev)) {
139                 BEGIN_LP_RING(4);
140
141                 OUT_RING(GFX_OP_DRAWRECT_INFO_I965);
142                 OUT_RING(0);
143                 OUT_RING(((sarea_priv->width - 1) & 0xffff) | ((sarea_priv->height - 1) << 16));
144                 OUT_RING(0);
145                 ADVANCE_LP_RING();
146         } else {
147                 BEGIN_LP_RING(6);
148
149                 OUT_RING(GFX_OP_DRAWRECT_INFO);
150                 OUT_RING(0);
151                 OUT_RING(0);
152                 OUT_RING(sarea_priv->width | sarea_priv->height << 16);
153                 OUT_RING(sarea_priv->width | sarea_priv->height << 16);
154                 OUT_RING(0);
155
156                 ADVANCE_LP_RING();
157         }
158
159         sarea_priv->ctxOwner = DRM_KERNEL_CONTEXT;
160
161         upper[0] = upper[1] = 0;
162         slice[0] = max(sarea_priv->pipeA_h / nhits, 1);
163         slice[1] = max(sarea_priv->pipeB_h / nhits, 1);
164         lower[0] = sarea_priv->pipeA_y + slice[0];
165         lower[1] = sarea_priv->pipeB_y + slice[0];
166
167         spin_lock(&dev->drw_lock);
168
169         /* Emit blits for buffer swaps, partitioning both outputs into as many
170          * slices as there are buffer swaps scheduled in order to avoid tearing
171          * (based on the assumption that a single buffer swap would always
172          * complete before scanout starts).
173          */
174         for (i = 0; i++ < nhits;
175              upper[0] = lower[0], lower[0] += slice[0],
176              upper[1] = lower[1], lower[1] += slice[1]) {
177                 if (i == nhits)
178                         lower[0] = lower[1] = sarea_priv->height;
179
180                 list_for_each(hit, &hits) {
181                         drm_i915_vbl_swap_t *swap_hit =
182                                 list_entry(hit, drm_i915_vbl_swap_t, head);
183                         struct drm_clip_rect *rect;
184                         int num_rects, pipe;
185                         unsigned short top, bottom;
186
187                         drw = drm_get_drawable_info(dev, swap_hit->drw_id);
188
189                         if (!drw)
190                                 continue;
191
192                         rect = drw->rects;
193                         pipe = swap_hit->pipe;
194                         top = upper[pipe];
195                         bottom = lower[pipe];
196
197                         for (num_rects = drw->num_rects; num_rects--; rect++) {
198                                 int y1 = max(rect->y1, top);
199                                 int y2 = min(rect->y2, bottom);
200
201                                 if (y1 >= y2)
202                                         continue;
203
204                                 BEGIN_LP_RING(8);
205
206                                 OUT_RING(cmd);
207                                 OUT_RING(ropcpp | dst_pitch);
208                                 OUT_RING((y1 << 16) | rect->x1);
209                                 OUT_RING((y2 << 16) | rect->x2);
210                                 OUT_RING(sarea_priv->front_offset);
211                                 OUT_RING((y1 << 16) | rect->x1);
212                                 OUT_RING(src_pitch);
213                                 OUT_RING(sarea_priv->back_offset);
214
215                                 ADVANCE_LP_RING();
216                         }
217                 }
218         }
219
220         spin_unlock_irqrestore(&dev->drw_lock, irqflags);
221
222         list_for_each_safe(hit, tmp, &hits) {
223                 drm_i915_vbl_swap_t *swap_hit =
224                         list_entry(hit, drm_i915_vbl_swap_t, head);
225
226                 list_del(hit);
227
228                 drm_free(swap_hit, sizeof(*swap_hit), DRM_MEM_DRIVER);
229         }
230 }
231
232 irqreturn_t i915_driver_irq_handler(DRM_IRQ_ARGS)
233 {
234         struct drm_device *dev = (struct drm_device *) arg;
235         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
236         u16 temp;
237         u32 pipea_stats, pipeb_stats;
238
239         pipea_stats = I915_READ(I915REG_PIPEASTAT);
240         pipeb_stats = I915_READ(I915REG_PIPEBSTAT);
241
242         temp = I915_READ16(I915REG_INT_IDENTITY_R);
243
244         temp &= (USER_INT_FLAG | VSYNC_PIPEA_FLAG | VSYNC_PIPEB_FLAG);
245
246         DRM_DEBUG("%s flag=%08x\n", __FUNCTION__, temp);
247
248         if (temp == 0)
249                 return IRQ_NONE;
250
251         I915_WRITE16(I915REG_INT_IDENTITY_R, temp);
252         (void) I915_READ16(I915REG_INT_IDENTITY_R);
253         DRM_READMEMORYBARRIER();
254
255         dev_priv->sarea_priv->last_dispatch = READ_BREADCRUMB(dev_priv);
256
257         if (temp & USER_INT_FLAG)
258                 DRM_WAKEUP(&dev_priv->irq_queue);
259
260         if (temp & (VSYNC_PIPEA_FLAG | VSYNC_PIPEB_FLAG)) {
261                 int vblank_pipe = dev_priv->vblank_pipe;
262
263                 if ((vblank_pipe &
264                      (DRM_I915_VBLANK_PIPE_A | DRM_I915_VBLANK_PIPE_B))
265                     == (DRM_I915_VBLANK_PIPE_A | DRM_I915_VBLANK_PIPE_B)) {
266                         if (temp & VSYNC_PIPEA_FLAG)
267                                 atomic_inc(&dev->vbl_received);
268                         if (temp & VSYNC_PIPEB_FLAG)
269                                 atomic_inc(&dev->vbl_received2);
270                 } else if (((temp & VSYNC_PIPEA_FLAG) &&
271                             (vblank_pipe & DRM_I915_VBLANK_PIPE_A)) ||
272                            ((temp & VSYNC_PIPEB_FLAG) &&
273                             (vblank_pipe & DRM_I915_VBLANK_PIPE_B)))
274                         atomic_inc(&dev->vbl_received);
275
276                 DRM_WAKEUP(&dev->vbl_queue);
277                 drm_vbl_send_signals(dev);
278
279                 if (dev_priv->swaps_pending > 0)
280                         drm_locked_tasklet(dev, i915_vblank_tasklet);
281                 I915_WRITE(I915REG_PIPEASTAT,
282                         pipea_stats|I915_VBLANK_INTERRUPT_ENABLE|
283                         I915_VBLANK_CLEAR);
284                 I915_WRITE(I915REG_PIPEBSTAT,
285                         pipeb_stats|I915_VBLANK_INTERRUPT_ENABLE|
286                         I915_VBLANK_CLEAR);
287         }
288
289         return IRQ_HANDLED;
290 }
291
292 static int i915_emit_irq(struct drm_device * dev)
293 {
294         drm_i915_private_t *dev_priv = dev->dev_private;
295         RING_LOCALS;
296
297         i915_kernel_lost_context(dev);
298
299         DRM_DEBUG("\n");
300
301         dev_priv->sarea_priv->last_enqueue = ++dev_priv->counter;
302
303         if (dev_priv->counter > 0x7FFFFFFFUL)
304                 dev_priv->sarea_priv->last_enqueue = dev_priv->counter = 1;
305
306         BEGIN_LP_RING(6);
307         OUT_RING(CMD_STORE_DWORD_IDX);
308         OUT_RING(20);
309         OUT_RING(dev_priv->counter);
310         OUT_RING(0);
311         OUT_RING(0);
312         OUT_RING(GFX_OP_USER_INTERRUPT);
313         ADVANCE_LP_RING();
314
315         return dev_priv->counter;
316 }
317
318 static int i915_wait_irq(struct drm_device * dev, int irq_nr)
319 {
320         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
321         int ret = 0;
322
323         DRM_DEBUG("irq_nr=%d breadcrumb=%d\n", irq_nr,
324                   READ_BREADCRUMB(dev_priv));
325
326         if (READ_BREADCRUMB(dev_priv) >= irq_nr)
327                 return 0;
328
329         dev_priv->sarea_priv->perf_boxes |= I915_BOX_WAIT;
330
331         DRM_WAIT_ON(ret, dev_priv->irq_queue, 3 * DRM_HZ,
332                     READ_BREADCRUMB(dev_priv) >= irq_nr);
333
334         if (ret == -EBUSY) {
335                 DRM_ERROR("EBUSY -- rec: %d emitted: %d\n",
336                           READ_BREADCRUMB(dev_priv), (int)dev_priv->counter);
337         }
338
339         dev_priv->sarea_priv->last_dispatch = READ_BREADCRUMB(dev_priv);
340         return ret;
341 }
342
343 static int i915_driver_vblank_do_wait(struct drm_device *dev, unsigned int *sequence,
344                                       atomic_t *counter)
345 {
346         drm_i915_private_t *dev_priv = dev->dev_private;
347         unsigned int cur_vblank;
348         int ret = 0;
349
350         if (!dev_priv) {
351                 DRM_ERROR("called with no initialization\n");
352                 return -EINVAL;
353         }
354
355         DRM_WAIT_ON(ret, dev->vbl_queue, 3 * DRM_HZ,
356                     (((cur_vblank = atomic_read(counter))
357                         - *sequence) <= (1<<23)));
358
359         *sequence = cur_vblank;
360
361         return ret;
362 }
363
364
365 int i915_driver_vblank_wait(struct drm_device *dev, unsigned int *sequence)
366 {
367         return i915_driver_vblank_do_wait(dev, sequence, &dev->vbl_received);
368 }
369
370 int i915_driver_vblank_wait2(struct drm_device *dev, unsigned int *sequence)
371 {
372         return i915_driver_vblank_do_wait(dev, sequence, &dev->vbl_received2);
373 }
374
375 /* Needs the lock as it touches the ring.
376  */
377 int i915_irq_emit(struct drm_device *dev, void *data,
378                          struct drm_file *file_priv)
379 {
380         drm_i915_private_t *dev_priv = dev->dev_private;
381         drm_i915_irq_emit_t *emit = data;
382         int result;
383
384         LOCK_TEST_WITH_RETURN(dev, file_priv);
385
386         if (!dev_priv) {
387                 DRM_ERROR("called with no initialization\n");
388                 return -EINVAL;
389         }
390
391         result = i915_emit_irq(dev);
392
393         if (DRM_COPY_TO_USER(emit->irq_seq, &result, sizeof(int))) {
394                 DRM_ERROR("copy_to_user\n");
395                 return -EFAULT;
396         }
397
398         return 0;
399 }
400
401 /* Doesn't need the hardware lock.
402  */
403 int i915_irq_wait(struct drm_device *dev, void *data,
404                          struct drm_file *file_priv)
405 {
406         drm_i915_private_t *dev_priv = dev->dev_private;
407         drm_i915_irq_wait_t *irqwait = data;
408
409         if (!dev_priv) {
410                 DRM_ERROR("called with no initialization\n");
411                 return -EINVAL;
412         }
413
414         return i915_wait_irq(dev, irqwait->irq_seq);
415 }
416
417 static void i915_enable_interrupt (struct drm_device *dev)
418 {
419         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
420         u16 flag;
421
422         flag = 0;
423         if (dev_priv->vblank_pipe & DRM_I915_VBLANK_PIPE_A)
424                 flag |= VSYNC_PIPEA_FLAG;
425         if (dev_priv->vblank_pipe & DRM_I915_VBLANK_PIPE_B)
426                 flag |= VSYNC_PIPEB_FLAG;
427
428         I915_WRITE16(I915REG_INT_ENABLE_R, USER_INT_FLAG | flag);
429 }
430
431 /* Set the vblank monitor pipe
432  */
433 int i915_vblank_pipe_set(struct drm_device *dev, void *data,
434                          struct drm_file *file_priv)
435 {
436         drm_i915_private_t *dev_priv = dev->dev_private;
437         drm_i915_vblank_pipe_t *pipe = data;
438
439         if (!dev_priv) {
440                 DRM_ERROR("called with no initialization\n");
441                 return -EINVAL;
442         }
443
444         if (pipe->pipe & ~(DRM_I915_VBLANK_PIPE_A|DRM_I915_VBLANK_PIPE_B)) {
445                 DRM_ERROR("called with invalid pipe 0x%x\n", pipe->pipe);
446                 return -EINVAL;
447         }
448
449         dev_priv->vblank_pipe = pipe->pipe;
450
451         i915_enable_interrupt (dev);
452
453         return 0;
454 }
455
456 int i915_vblank_pipe_get(struct drm_device *dev, void *data,
457                          struct drm_file *file_priv)
458 {
459         drm_i915_private_t *dev_priv = dev->dev_private;
460         drm_i915_vblank_pipe_t *pipe = data;
461         u16 flag;
462
463         if (!dev_priv) {
464                 DRM_ERROR("called with no initialization\n");
465                 return -EINVAL;
466         }
467
468         flag = I915_READ(I915REG_INT_ENABLE_R);
469         pipe->pipe = 0;
470         if (flag & VSYNC_PIPEA_FLAG)
471                 pipe->pipe |= DRM_I915_VBLANK_PIPE_A;
472         if (flag & VSYNC_PIPEB_FLAG)
473                 pipe->pipe |= DRM_I915_VBLANK_PIPE_B;
474
475         return 0;
476 }
477
478 /**
479  * Schedule buffer swap at given vertical blank.
480  */
481 int i915_vblank_swap(struct drm_device *dev, void *data,
482                      struct drm_file *file_priv)
483 {
484         drm_i915_private_t *dev_priv = dev->dev_private;
485         drm_i915_vblank_swap_t *swap = data;
486         drm_i915_vbl_swap_t *vbl_swap;
487         unsigned int pipe, seqtype, curseq;
488         unsigned long irqflags;
489         struct list_head *list;
490
491         if (!dev_priv) {
492                 DRM_ERROR("%s called with no initialization\n", __func__);
493                 return -EINVAL;
494         }
495
496         if (dev_priv->sarea_priv->rotation) {
497                 DRM_DEBUG("Rotation not supported\n");
498                 return -EINVAL;
499         }
500
501         if (swap->seqtype & ~(_DRM_VBLANK_RELATIVE | _DRM_VBLANK_ABSOLUTE |
502                              _DRM_VBLANK_SECONDARY | _DRM_VBLANK_NEXTONMISS)) {
503                 DRM_ERROR("Invalid sequence type 0x%x\n", swap->seqtype);
504                 return -EINVAL;
505         }
506
507         pipe = (swap->seqtype & _DRM_VBLANK_SECONDARY) ? 1 : 0;
508
509         seqtype = swap->seqtype & (_DRM_VBLANK_RELATIVE | _DRM_VBLANK_ABSOLUTE);
510
511         if (!(dev_priv->vblank_pipe & (1 << pipe))) {
512                 DRM_ERROR("Invalid pipe %d\n", pipe);
513                 return -EINVAL;
514         }
515
516         spin_lock_irqsave(&dev->drw_lock, irqflags);
517
518         if (!drm_get_drawable_info(dev, swap->drawable)) {
519                 spin_unlock_irqrestore(&dev->drw_lock, irqflags);
520                 DRM_DEBUG("Invalid drawable ID %d\n", swap->drawable);
521                 return -EINVAL;
522         }
523
524         spin_unlock_irqrestore(&dev->drw_lock, irqflags);
525
526         curseq = atomic_read(pipe ? &dev->vbl_received2 : &dev->vbl_received);
527
528         if (seqtype == _DRM_VBLANK_RELATIVE)
529                 swap->sequence += curseq;
530
531         if ((curseq - swap->sequence) <= (1<<23)) {
532                 if (swap->seqtype & _DRM_VBLANK_NEXTONMISS) {
533                         swap->sequence = curseq + 1;
534                 } else {
535                         DRM_DEBUG("Missed target sequence\n");
536                         return -EINVAL;
537                 }
538         }
539
540         spin_lock_irqsave(&dev_priv->swaps_lock, irqflags);
541
542         list_for_each(list, &dev_priv->vbl_swaps.head) {
543                 vbl_swap = list_entry(list, drm_i915_vbl_swap_t, head);
544
545                 if (vbl_swap->drw_id == swap->drawable &&
546                     vbl_swap->pipe == pipe &&
547                     vbl_swap->sequence == swap->sequence) {
548                         spin_unlock_irqrestore(&dev_priv->swaps_lock, irqflags);
549                         DRM_DEBUG("Already scheduled\n");
550                         return 0;
551                 }
552         }
553
554         spin_unlock_irqrestore(&dev_priv->swaps_lock, irqflags);
555
556         if (dev_priv->swaps_pending >= 100) {
557                 DRM_DEBUG("Too many swaps queued\n");
558                 return -EBUSY;
559         }
560
561         vbl_swap = drm_calloc(1, sizeof(*vbl_swap), DRM_MEM_DRIVER);
562
563         if (!vbl_swap) {
564                 DRM_ERROR("Failed to allocate memory to queue swap\n");
565                 return -ENOMEM;
566         }
567
568         DRM_DEBUG("\n");
569
570         vbl_swap->drw_id = swap->drawable;
571         vbl_swap->pipe = pipe;
572         vbl_swap->sequence = swap->sequence;
573
574         spin_lock_irqsave(&dev_priv->swaps_lock, irqflags);
575
576         list_add_tail(&vbl_swap->head, &dev_priv->vbl_swaps.head);
577         dev_priv->swaps_pending++;
578
579         spin_unlock_irqrestore(&dev_priv->swaps_lock, irqflags);
580
581         return 0;
582 }
583
584 /* drm_dma.h hooks
585 */
586 void i915_driver_irq_preinstall(struct drm_device * dev)
587 {
588         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
589
590         I915_WRITE16(I915REG_HWSTAM, 0xfffe);
591         I915_WRITE16(I915REG_INT_MASK_R, 0x0);
592         I915_WRITE16(I915REG_INT_ENABLE_R, 0x0);
593 }
594
595 void i915_driver_irq_postinstall(struct drm_device * dev)
596 {
597         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
598
599         spin_lock_init(&dev_priv->swaps_lock);
600         INIT_LIST_HEAD(&dev_priv->vbl_swaps.head);
601         dev_priv->swaps_pending = 0;
602
603         if (!dev_priv->vblank_pipe)
604                 dev_priv->vblank_pipe = DRM_I915_VBLANK_PIPE_A;
605         i915_enable_interrupt(dev);
606         DRM_INIT_WAITQUEUE(&dev_priv->irq_queue);
607 }
608
609 void i915_driver_irq_uninstall(struct drm_device * dev)
610 {
611         drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
612         u16 temp;
613
614         if (!dev_priv)
615                 return;
616
617         I915_WRITE16(I915REG_HWSTAM, 0xffff);
618         I915_WRITE16(I915REG_INT_MASK_R, 0xffff);
619         I915_WRITE16(I915REG_INT_ENABLE_R, 0x0);
620
621         temp = I915_READ16(I915REG_INT_IDENTITY_R);
622         I915_WRITE16(I915REG_INT_IDENTITY_R, temp);
623 }