OvmfPkg/Include/IndustryStandard/Xen/io/ring.h

   1 /******************************************************************************
   2  * ring.h
   3  *
   4  * Shared producer-consumer ring macros.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to
   8  * deal in the Software without restriction, including without limitation the
   9  * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
  10  * sell copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  22  * DEALINGS IN THE SOFTWARE.
  23  *
  24  * Tim Deegan and Andrew Warfield November 2004.
  25  */
  26
  27 #ifndef __XEN_PUBLIC_IO_RING_H__
  28 #define __XEN_PUBLIC_IO_RING_H__
  29
  30 #include "../xen-compat.h"
  31
  32 #if __XEN_INTERFACE_VERSION__ < 0x00030208
  33 #define xen_mb()  mb()
  34 #define xen_rmb() rmb()
  35 #define xen_wmb() wmb()
  36 #endif
  37
  38 typedef UINT32 RING_IDX;
  39
  40 /* Round a 32-bit unsigned constant down to the nearest power of two. */
  41 #define __RD2(_x)  (((_x) & 0x00000002) ? 0x2                  : ((_x) & 0x1))
  42 #define __RD4(_x)  (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2    : __RD2(_x))
  43 #define __RD8(_x)  (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4    : __RD4(_x))
  44 #define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8    : __RD8(_x))
  45 #define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
  46
  47 /*
  48  * Calculate size of a shared ring, given the total available space for the
  49  * ring and indexes (_sz), and the name tag of the request/response structure.
  50  * A ring contains as many entries as will fit, rounded down to the nearest
  51  * power of two (so we can mask with (size-1) to loop around).
  52  */
  53 #define __CONST_RING_SIZE(_s, _sz) \
  54     (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
  55             sizeof(((struct _s##_sring *)0)->ring[0])))
  56 /*
  57  * The same for passing in an actual pointer instead of a name tag.
  58  */
  59 #define __RING_SIZE(_s, _sz) \
  60     (__RD32(((_sz) - (INTN)(_s)->ring + (INTN)(_s)) / sizeof((_s)->ring[0])))
  61
  62 /*
  63  * Macros to make the correct C datatypes for a new kind of ring.
  64  *
  65  * To make a new ring datatype, you need to have two message structures,
  66  * let's say request_t, and response_t already defined.
  67  *
  68  * In a header where you want the ring datatype declared, you then do:
  69  *
  70  *     DEFINE_RING_TYPES(mytag, request_t, response_t);
  71  *
  72  * These expand out to give you a set of types, as you can see below.
  73  * The most important of these are:
  74  *
  75  *     mytag_sring_t      - The shared ring.
  76  *     mytag_front_ring_t - The 'front' half of the ring.
  77  *     mytag_back_ring_t  - The 'back' half of the ring.
  78  *
  79  * To initialize a ring in your code you need to know the location and size
  80  * of the shared memory area (PAGE_SIZE, for instance). To initialise
  81  * the front half:
  82  *
  83  *     mytag_front_ring_t front_ring;
  84  *     SHARED_RING_INIT((mytag_sring_t *)shared_page);
  85  *     FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
  86  *
  87  * Initializing the back follows similarly (note that only the front
  88  * initializes the shared ring):
  89  *
  90  *     mytag_back_ring_t back_ring;
  91  *     BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
  92  */
  93
  94 #define DEFINE_RING_TYPES(__name, __req_t, __rsp_t)                     \
  95                                                                         \
  96 /* Shared ring entry */                                                 \
  97 union __name##_sring_entry {                                            \
  98     __req_t req;                                                        \
  99     __rsp_t rsp;                                                        \
 100 };                                                                      \
 101                                                                         \
 102 /* Shared ring page */                                                  \
 103 struct __name##_sring {                                                 \
 104     RING_IDX req_prod, req_event;                                       \
 105     RING_IDX rsp_prod, rsp_event;                                       \
 106     union {                                                             \
 107         struct {                                                        \
 108             UINT8 smartpoll_active;                                   \
 109         } netif;                                                        \
 110         struct {                                                        \
 111             UINT8 msg;                                                \
 112         } tapif_user;                                                   \
 113         UINT8 pvt_pad[4];                                             \
 114     } private;                                                          \
 115     UINT8 __pad[44];                                                  \
 116     union __name##_sring_entry ring[1]; /* variable-length */           \
 117 };                                                                      \
 118                                                                         \
 119 /* "Front" end's private variables */                                   \
 120 struct __name##_front_ring {                                            \
 121     RING_IDX req_prod_pvt;                                              \
 122     RING_IDX rsp_cons;                                                  \
 123     UINT32 nr_ents;                                               \
 124     struct __name##_sring *sring;                                       \
 125 };                                                                      \
 126                                                                         \
 127 /* "Back" end's private variables */                                    \
 128 struct __name##_back_ring {                                             \
 129     RING_IDX rsp_prod_pvt;                                              \
 130     RING_IDX req_cons;                                                  \
 131     UINT32 nr_ents;                                               \
 132     struct __name##_sring *sring;                                       \
 133 };                                                                      \
 134                                                                         \
 135 /* Syntactic sugar */                                                   \
 136 typedef struct __name##_sring __name##_sring_t;                         \
 137 typedef struct __name##_front_ring __name##_front_ring_t;               \
 138 typedef struct __name##_back_ring __name##_back_ring_t
 139
 140 /*
 141  * Macros for manipulating rings.
 142  *
 143  * FRONT_RING_whatever works on the "front end" of a ring: here
 144  * requests are pushed on to the ring and responses taken off it.
 145  *
 146  * BACK_RING_whatever works on the "back end" of a ring: here
 147  * requests are taken off the ring and responses put on.
 148  *
 149  * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
 150  * This is OK in 1-for-1 request-response situations where the
 151  * requestor (front end) never has more than RING_SIZE()-1
 152  * outstanding requests.
 153  */
 154
 155 /* Initialising empty rings */
 156 #define SHARED_RING_INIT(_s) do {                                       \
 157     (_s)->req_prod  = (_s)->rsp_prod  = 0;                              \
 158     (_s)->req_event = (_s)->rsp_event = 1;                              \
 159     (VOID)ZeroMem((_s)->private.pvt_pad, sizeof((_s)->private.pvt_pad)); \
 160     (VOID)ZeroMem((_s)->__pad, sizeof((_s)->__pad));                  \
 161 } while(0)
 162
 163 #define FRONT_RING_INIT(_r, _s, __size) do {                            \
 164     (_r)->req_prod_pvt = 0;                                             \
 165     (_r)->rsp_cons = 0;                                                 \
 166     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 167     (_r)->sring = (_s);                                                 \
 168 } while (0)
 169
 170 #define BACK_RING_INIT(_r, _s, __size) do {                             \
 171     (_r)->rsp_prod_pvt = 0;                                             \
 172     (_r)->req_cons = 0;                                                 \
 173     (_r)->nr_ents = __RING_SIZE(_s, __size);                            \
 174     (_r)->sring = (_s);                                                 \
 175 } while (0)
 176
 177 /* How big is this ring? */
 178 #define RING_SIZE(_r)                                                   \
 179     ((_r)->nr_ents)
 180
 181 /* Number of free requests (for use on front side only). */
 182 #define RING_FREE_REQUESTS(_r)                                          \
 183     (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
 184
 185 /* Test if there is an empty slot available on the front ring.
 186  * (This is only meaningful from the front. )
 187  */
 188 #define RING_FULL(_r)                                                   \
 189     (RING_FREE_REQUESTS(_r) == 0)
 190
 191 /* Test if there are outstanding messages to be processed on a ring. */
 192 #define RING_HAS_UNCONSUMED_RESPONSES(_r)                               \
 193     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
 194
 195 #ifdef __GNUC__
 196 #define RING_HAS_UNCONSUMED_REQUESTS(_r) ({                             \
 197     UINT32 req = (_r)->sring->req_prod - (_r)->req_cons;          \
 198     UINT32 rsp = RING_SIZE(_r) -                                  \
 199         ((_r)->req_cons - (_r)->rsp_prod_pvt);                          \
 200     req < rsp ? req : rsp;                                              \
 201 })
 202 #else
 203 /* Same as above, but without the nice GCC ({ ... }) syntax. */
 204 #define RING_HAS_UNCONSUMED_REQUESTS(_r)                                \
 205     ((((_r)->sring->req_prod - (_r)->req_cons) <                        \
 206       (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ?        \
 207      ((_r)->sring->req_prod - (_r)->req_cons) :                         \
 208      (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
 209 #endif
 210
 211 /* Direct access to individual ring elements, by index. */
 212 #define RING_GET_REQUEST(_r, _idx)                                      \
 213     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
 214
 215 #define RING_GET_RESPONSE(_r, _idx)                                     \
 216     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
 217
 218 /* Loop termination condition: Would the specified index overflow the ring? */
 219 #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
 220     (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
 221
 222 /* Ill-behaved frontend determination: Can there be this many requests? */
 223 #define RING_REQUEST_PROD_OVERFLOW(_r, _prod)                           \
 224     (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
 225
 226 #define RING_PUSH_REQUESTS(_r) do {                                     \
 227     xen_wmb(); /* back sees requests /before/ updated producer index */ \
 228     (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
 229 } while (0)
 230
 231 #define RING_PUSH_RESPONSES(_r) do {                                    \
 232     xen_wmb(); /* front sees resps /before/ updated producer index */   \
 233     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;                         \
 234 } while (0)
 235
 236 /*
 237  * Notification hold-off (req_event and rsp_event):
 238  *
 239  * When queueing requests or responses on a shared ring, it may not always be
 240  * necessary to notify the remote end. For example, if requests are in flight
 241  * in a backend, the front may be able to queue further requests without
 242  * notifying the back (if the back checks for new requests when it queues
 243  * responses).
 244  *
 245  * When enqueuing requests or responses:
 246  *
 247  *  Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
 248  *  is a boolean return value. True indicates that the receiver requires an
 249  *  asynchronous notification.
 250  *
 251  * After dequeuing requests or responses (before sleeping the connection):
 252  *
 253  *  Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
 254  *  The second argument is a boolean return value. True indicates that there
 255  *  are pending messages on the ring (i.e., the connection should not be put
 256  *  to sleep).
 257  *
 258  *  These macros will set the req_event/rsp_event field to trigger a
 259  *  notification on the very next message that is enqueued. If you want to
 260  *  create batches of work (i.e., only receive a notification after several
 261  *  messages have been enqueued) then you will need to create a customised
 262  *  version of the FINAL_CHECK macro in your own code, which sets the event
 263  *  field appropriately.
 264  */
 265
 266 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {           \
 267     RING_IDX __old = (_r)->sring->req_prod;                             \
 268     RING_IDX __new = (_r)->req_prod_pvt;                                \
 269     xen_wmb(); /* back sees requests /before/ updated producer index */ \
 270     (_r)->sring->req_prod = __new;                                      \
 271     xen_mb(); /* back sees new requests /before/ we check req_event */  \
 272     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <           \
 273                  (RING_IDX)(__new - __old));                            \
 274 } while (0)
 275
 276 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {          \
 277     RING_IDX __old = (_r)->sring->rsp_prod;                             \
 278     RING_IDX __new = (_r)->rsp_prod_pvt;                                \
 279     xen_wmb(); /* front sees resps /before/ updated producer index */   \
 280     (_r)->sring->rsp_prod = __new;                                      \
 281     xen_mb(); /* front sees new resps /before/ we check rsp_event */    \
 282     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <           \
 283                  (RING_IDX)(__new - __old));                            \
 284 } while (0)
 285
 286 #define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do {             \
 287     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 288     if (_work_to_do) break;                                             \
 289     (_r)->sring->req_event = (_r)->req_cons + 1;                        \
 290     xen_mb();                                                           \
 291     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);                   \
 292 } while (0)
 293
 294 #define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do {            \
 295     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 296     if (_work_to_do) break;                                             \
 297     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;                        \
 298     xen_mb();                                                           \
 299     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);                  \
 300 } while (0)
 301
 302 #endif /* __XEN_PUBLIC_IO_RING_H__ */
 303
 304 /*
 305  * Local variables:
 306  * mode: C
 307  * c-file-style: "BSD"
 308  * c-basic-offset: 4
 309  * tab-width: 4
 310  * indent-tabs-mode: nil
 311  * End:
 312  */