Drivers: hv: vmbus: Fix a bug in hv_need_to_signal()
[linux-3.10.git] / drivers / hv / ring_buffer.c
1 /*
2  *
3  * Copyright (c) 2009, Microsoft Corporation.
4  *
5  * This program is free software; you can redistribute it and/or modify it
6  * under the terms and conditions of the GNU General Public License,
7  * version 2, as published by the Free Software Foundation.
8  *
9  * This program is distributed in the hope it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
12  * more details.
13  *
14  * You should have received a copy of the GNU General Public License along with
15  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
16  * Place - Suite 330, Boston, MA 02111-1307 USA.
17  *
18  * Authors:
19  *   Haiyang Zhang <haiyangz@microsoft.com>
20  *   Hank Janssen  <hjanssen@microsoft.com>
21  *   K. Y. Srinivasan <kys@microsoft.com>
22  *
23  */
24 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
25
26 #include <linux/kernel.h>
27 #include <linux/mm.h>
28 #include <linux/hyperv.h>
29
30 #include "hyperv_vmbus.h"
31
32 void hv_begin_read(struct hv_ring_buffer_info *rbi)
33 {
34         rbi->ring_buffer->interrupt_mask = 1;
35         smp_mb();
36 }
37
38 u32 hv_end_read(struct hv_ring_buffer_info *rbi)
39 {
40         u32 read;
41         u32 write;
42
43         rbi->ring_buffer->interrupt_mask = 0;
44         smp_mb();
45
46         /*
47          * Now check to see if the ring buffer is still empty.
48          * If it is not, we raced and we need to process new
49          * incoming messages.
50          */
51         hv_get_ringbuffer_availbytes(rbi, &read, &write);
52
53         return read;
54 }
55
56 /*
57  * When we write to the ring buffer, check if the host needs to
58  * be signaled. Here is the details of this protocol:
59  *
60  *      1. The host guarantees that while it is draining the
61  *         ring buffer, it will set the interrupt_mask to
62  *         indicate it does not need to be interrupted when
63  *         new data is placed.
64  *
65  *      2. The host guarantees that it will completely drain
66  *         the ring buffer before exiting the read loop. Further,
67  *         once the ring buffer is empty, it will clear the
68  *         interrupt_mask and re-check to see if new data has
69  *         arrived.
70  */
71
72 static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
73 {
74         smp_mb();
75         if (rbi->ring_buffer->interrupt_mask)
76                 return false;
77
78         /*
79          * This is the only case we need to signal when the
80          * ring transitions from being empty to non-empty.
81          */
82         if (old_write == rbi->ring_buffer->read_index)
83                 return true;
84
85         return false;
86 }
87
88 /*
89  * To optimize the flow management on the send-side,
90  * when the sender is blocked because of lack of
91  * sufficient space in the ring buffer, potential the
92  * consumer of the ring buffer can signal the producer.
93  * This is controlled by the following parameters:
94  *
95  * 1. pending_send_sz: This is the size in bytes that the
96  *    producer is trying to send.
97  * 2. The feature bit feat_pending_send_sz set to indicate if
98  *    the consumer of the ring will signal when the ring
99  *    state transitions from being full to a state where
100  *    there is room for the producer to send the pending packet.
101  */
102
103 static bool hv_need_to_signal_on_read(u32 old_rd,
104                                          struct hv_ring_buffer_info *rbi)
105 {
106         u32 prev_write_sz;
107         u32 cur_write_sz;
108         u32 r_size;
109         u32 write_loc = rbi->ring_buffer->write_index;
110         u32 read_loc = rbi->ring_buffer->read_index;
111         u32 pending_sz = rbi->ring_buffer->pending_send_sz;
112
113         /*
114          * If the other end is not blocked on write don't bother.
115          */
116         if (pending_sz == 0)
117                 return false;
118
119         r_size = rbi->ring_datasize;
120         cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
121                         read_loc - write_loc;
122
123         prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
124                         old_rd - write_loc;
125
126
127         if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
128                 return true;
129
130         return false;
131 }
132
133 /*
134  * hv_get_next_write_location()
135  *
136  * Get the next write location for the specified ring buffer
137  *
138  */
139 static inline u32
140 hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
141 {
142         u32 next = ring_info->ring_buffer->write_index;
143
144         return next;
145 }
146
147 /*
148  * hv_set_next_write_location()
149  *
150  * Set the next write location for the specified ring buffer
151  *
152  */
153 static inline void
154 hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
155                      u32 next_write_location)
156 {
157         ring_info->ring_buffer->write_index = next_write_location;
158 }
159
160 /*
161  * hv_get_next_read_location()
162  *
163  * Get the next read location for the specified ring buffer
164  */
165 static inline u32
166 hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
167 {
168         u32 next = ring_info->ring_buffer->read_index;
169
170         return next;
171 }
172
173 /*
174  * hv_get_next_readlocation_withoffset()
175  *
176  * Get the next read location + offset for the specified ring buffer.
177  * This allows the caller to skip
178  */
179 static inline u32
180 hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
181                                  u32 offset)
182 {
183         u32 next = ring_info->ring_buffer->read_index;
184
185         next += offset;
186         next %= ring_info->ring_datasize;
187
188         return next;
189 }
190
191 /*
192  *
193  * hv_set_next_read_location()
194  *
195  * Set the next read location for the specified ring buffer
196  *
197  */
198 static inline void
199 hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
200                     u32 next_read_location)
201 {
202         ring_info->ring_buffer->read_index = next_read_location;
203 }
204
205
206 /*
207  *
208  * hv_get_ring_buffer()
209  *
210  * Get the start of the ring buffer
211  */
212 static inline void *
213 hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
214 {
215         return (void *)ring_info->ring_buffer->buffer;
216 }
217
218
219 /*
220  *
221  * hv_get_ring_buffersize()
222  *
223  * Get the size of the ring buffer
224  */
225 static inline u32
226 hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
227 {
228         return ring_info->ring_datasize;
229 }
230
231 /*
232  *
233  * hv_get_ring_bufferindices()
234  *
235  * Get the read and write indices as u64 of the specified ring buffer
236  *
237  */
238 static inline u64
239 hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
240 {
241         return (u64)ring_info->ring_buffer->write_index << 32;
242 }
243
244 /*
245  *
246  * hv_copyfrom_ringbuffer()
247  *
248  * Helper routine to copy to source from ring buffer.
249  * Assume there is enough room. Handles wrap-around in src case only!!
250  *
251  */
252 static u32 hv_copyfrom_ringbuffer(
253         struct hv_ring_buffer_info      *ring_info,
254         void                            *dest,
255         u32                             destlen,
256         u32                             start_read_offset)
257 {
258         void *ring_buffer = hv_get_ring_buffer(ring_info);
259         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
260
261         u32 frag_len;
262
263         /* wrap-around detected at the src */
264         if (destlen > ring_buffer_size - start_read_offset) {
265                 frag_len = ring_buffer_size - start_read_offset;
266
267                 memcpy(dest, ring_buffer + start_read_offset, frag_len);
268                 memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
269         } else
270
271                 memcpy(dest, ring_buffer + start_read_offset, destlen);
272
273
274         start_read_offset += destlen;
275         start_read_offset %= ring_buffer_size;
276
277         return start_read_offset;
278 }
279
280
281 /*
282  *
283  * hv_copyto_ringbuffer()
284  *
285  * Helper routine to copy from source to ring buffer.
286  * Assume there is enough room. Handles wrap-around in dest case only!!
287  *
288  */
289 static u32 hv_copyto_ringbuffer(
290         struct hv_ring_buffer_info      *ring_info,
291         u32                             start_write_offset,
292         void                            *src,
293         u32                             srclen)
294 {
295         void *ring_buffer = hv_get_ring_buffer(ring_info);
296         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
297         u32 frag_len;
298
299         /* wrap-around detected! */
300         if (srclen > ring_buffer_size - start_write_offset) {
301                 frag_len = ring_buffer_size - start_write_offset;
302                 memcpy(ring_buffer + start_write_offset, src, frag_len);
303                 memcpy(ring_buffer, src + frag_len, srclen - frag_len);
304         } else
305                 memcpy(ring_buffer + start_write_offset, src, srclen);
306
307         start_write_offset += srclen;
308         start_write_offset %= ring_buffer_size;
309
310         return start_write_offset;
311 }
312
313 /*
314  *
315  * hv_ringbuffer_get_debuginfo()
316  *
317  * Get various debug metrics for the specified ring buffer
318  *
319  */
320 void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
321                             struct hv_ring_buffer_debug_info *debug_info)
322 {
323         u32 bytes_avail_towrite;
324         u32 bytes_avail_toread;
325
326         if (ring_info->ring_buffer) {
327                 hv_get_ringbuffer_availbytes(ring_info,
328                                         &bytes_avail_toread,
329                                         &bytes_avail_towrite);
330
331                 debug_info->bytes_avail_toread = bytes_avail_toread;
332                 debug_info->bytes_avail_towrite = bytes_avail_towrite;
333                 debug_info->current_read_index =
334                         ring_info->ring_buffer->read_index;
335                 debug_info->current_write_index =
336                         ring_info->ring_buffer->write_index;
337                 debug_info->current_interrupt_mask =
338                         ring_info->ring_buffer->interrupt_mask;
339         }
340 }
341
342 /*
343  *
344  * hv_ringbuffer_init()
345  *
346  *Initialize the ring buffer
347  *
348  */
349 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
350                    void *buffer, u32 buflen)
351 {
352         if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
353                 return -EINVAL;
354
355         memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
356
357         ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
358         ring_info->ring_buffer->read_index =
359                 ring_info->ring_buffer->write_index = 0;
360
361         ring_info->ring_size = buflen;
362         ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);
363
364         spin_lock_init(&ring_info->ring_lock);
365
366         return 0;
367 }
368
369 /*
370  *
371  * hv_ringbuffer_cleanup()
372  *
373  * Cleanup the ring buffer
374  *
375  */
376 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
377 {
378 }
379
380 /*
381  *
382  * hv_ringbuffer_write()
383  *
384  * Write to the ring buffer
385  *
386  */
387 int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
388                     struct scatterlist *sglist, u32 sgcount, bool *signal)
389 {
390         int i = 0;
391         u32 bytes_avail_towrite;
392         u32 bytes_avail_toread;
393         u32 totalbytes_towrite = 0;
394
395         struct scatterlist *sg;
396         u32 next_write_location;
397         u32 old_write;
398         u64 prev_indices = 0;
399         unsigned long flags;
400
401         for_each_sg(sglist, sg, sgcount, i)
402         {
403                 totalbytes_towrite += sg->length;
404         }
405
406         totalbytes_towrite += sizeof(u64);
407
408         spin_lock_irqsave(&outring_info->ring_lock, flags);
409
410         hv_get_ringbuffer_availbytes(outring_info,
411                                 &bytes_avail_toread,
412                                 &bytes_avail_towrite);
413
414
415         /* If there is only room for the packet, assume it is full. */
416         /* Otherwise, the next time around, we think the ring buffer */
417         /* is empty since the read index == write index */
418         if (bytes_avail_towrite <= totalbytes_towrite) {
419                 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
420                 return -EAGAIN;
421         }
422
423         /* Write to the ring buffer */
424         next_write_location = hv_get_next_write_location(outring_info);
425
426         old_write = next_write_location;
427
428         for_each_sg(sglist, sg, sgcount, i)
429         {
430                 next_write_location = hv_copyto_ringbuffer(outring_info,
431                                                      next_write_location,
432                                                      sg_virt(sg),
433                                                      sg->length);
434         }
435
436         /* Set previous packet start */
437         prev_indices = hv_get_ring_bufferindices(outring_info);
438
439         next_write_location = hv_copyto_ringbuffer(outring_info,
440                                              next_write_location,
441                                              &prev_indices,
442                                              sizeof(u64));
443
444         /* Issue a full memory barrier before updating the write index */
445         smp_mb();
446
447         /* Now, update the write location */
448         hv_set_next_write_location(outring_info, next_write_location);
449
450
451         spin_unlock_irqrestore(&outring_info->ring_lock, flags);
452
453         *signal = hv_need_to_signal(old_write, outring_info);
454         return 0;
455 }
456
457
458 /*
459  *
460  * hv_ringbuffer_peek()
461  *
462  * Read without advancing the read index
463  *
464  */
465 int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
466                    void *Buffer, u32 buflen)
467 {
468         u32 bytes_avail_towrite;
469         u32 bytes_avail_toread;
470         u32 next_read_location = 0;
471         unsigned long flags;
472
473         spin_lock_irqsave(&Inring_info->ring_lock, flags);
474
475         hv_get_ringbuffer_availbytes(Inring_info,
476                                 &bytes_avail_toread,
477                                 &bytes_avail_towrite);
478
479         /* Make sure there is something to read */
480         if (bytes_avail_toread < buflen) {
481
482                 spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
483
484                 return -EAGAIN;
485         }
486
487         /* Convert to byte offset */
488         next_read_location = hv_get_next_read_location(Inring_info);
489
490         next_read_location = hv_copyfrom_ringbuffer(Inring_info,
491                                                 Buffer,
492                                                 buflen,
493                                                 next_read_location);
494
495         spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
496
497         return 0;
498 }
499
500
501 /*
502  *
503  * hv_ringbuffer_read()
504  *
505  * Read and advance the read index
506  *
507  */
508 int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
509                    u32 buflen, u32 offset, bool *signal)
510 {
511         u32 bytes_avail_towrite;
512         u32 bytes_avail_toread;
513         u32 next_read_location = 0;
514         u64 prev_indices = 0;
515         unsigned long flags;
516         u32 old_read;
517
518         if (buflen <= 0)
519                 return -EINVAL;
520
521         spin_lock_irqsave(&inring_info->ring_lock, flags);
522
523         hv_get_ringbuffer_availbytes(inring_info,
524                                 &bytes_avail_toread,
525                                 &bytes_avail_towrite);
526
527         old_read = bytes_avail_toread;
528
529         /* Make sure there is something to read */
530         if (bytes_avail_toread < buflen) {
531                 spin_unlock_irqrestore(&inring_info->ring_lock, flags);
532
533                 return -EAGAIN;
534         }
535
536         next_read_location =
537                 hv_get_next_readlocation_withoffset(inring_info, offset);
538
539         next_read_location = hv_copyfrom_ringbuffer(inring_info,
540                                                 buffer,
541                                                 buflen,
542                                                 next_read_location);
543
544         next_read_location = hv_copyfrom_ringbuffer(inring_info,
545                                                 &prev_indices,
546                                                 sizeof(u64),
547                                                 next_read_location);
548
549         /* Make sure all reads are done before we update the read index since */
550         /* the writer may start writing to the read area once the read index */
551         /*is updated */
552         smp_mb();
553
554         /* Update the read index */
555         hv_set_next_read_location(inring_info, next_read_location);
556
557         spin_unlock_irqrestore(&inring_info->ring_lock, flags);
558
559         *signal = hv_need_to_signal_on_read(old_read, inring_info);
560
561         return 0;
562 }