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

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