sound/firewire/iso-resources.c

   1 /*
   2  * isochronous resources helper functions
   3  *
   4  * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
   5  * Licensed under the terms of the GNU General Public License, version 2.
   6  */
   7
   8 #include <linux/device.h>
   9 #include <linux/firewire.h>
  10 #include <linux/firewire-constants.h>
  11 #include <linux/export.h>
  12 #include <linux/jiffies.h>
  13 #include <linux/mutex.h>
  14 #include <linux/sched.h>
  15 #include <linux/spinlock.h>
  16 #include "iso-resources.h"
  17
  18 /**
  19  * fw_iso_resources_init - initializes a &struct fw_iso_resources
  20  * @r: the resource manager to initialize
  21  * @unit: the device unit for which the resources will be needed
  22  *
  23  * If the device does not support all channel numbers, change @r->channels_mask
  24  * after calling this function.
  25  */
  26 int fw_iso_resources_init(struct fw_iso_resources *r, struct fw_unit *unit)
  27 {
  28         r->channels_mask = ~0uLL;
  29         r->unit = fw_unit_get(unit);
  30         mutex_init(&r->mutex);
  31         r->allocated = false;
  32
  33         return 0;
  34 }
  35 EXPORT_SYMBOL(fw_iso_resources_init);
  36
  37 /**
  38  * fw_iso_resources_destroy - destroy a resource manager
  39  * @r: the resource manager that is no longer needed
  40  */
  41 void fw_iso_resources_destroy(struct fw_iso_resources *r)
  42 {
  43         WARN_ON(r->allocated);
  44         mutex_destroy(&r->mutex);
  45         fw_unit_put(r->unit);
  46 }
  47 EXPORT_SYMBOL(fw_iso_resources_destroy);
  48
  49 static unsigned int packet_bandwidth(unsigned int max_payload_bytes, int speed)
  50 {
  51         unsigned int bytes, s400_bytes;
  52
  53         /* iso packets have three header quadlets and quadlet-aligned payload */
  54         bytes = 3 * 4 + ALIGN(max_payload_bytes, 4);
  55
  56         /* convert to bandwidth units (quadlets at S1600 = bytes at S400) */
  57         if (speed <= SCODE_400)
  58                 s400_bytes = bytes * (1 << (SCODE_400 - speed));
  59         else
  60                 s400_bytes = DIV_ROUND_UP(bytes, 1 << (speed - SCODE_400));
  61
  62         return s400_bytes;
  63 }
  64
  65 static int current_bandwidth_overhead(struct fw_card *card)
  66 {
  67         /*
  68          * Under the usual pessimistic assumption (cable length 4.5 m), the
  69          * isochronous overhead for N cables is 1.797 µs + N * 0.494 µs, or
  70          * 88.3 + N * 24.3 in bandwidth units.
  71          *
  72          * The calculation below tries to deduce N from the current gap count.
  73          * If the gap count has been optimized by measuring the actual packet
  74          * transmission time, this derived overhead should be near the actual
  75          * overhead as well.
  76          */
  77         return card->gap_count < 63 ? card->gap_count * 97 / 10 + 89 : 512;
  78 }
  79
  80 static int wait_isoch_resource_delay_after_bus_reset(struct fw_card *card)
  81 {
  82         for (;;) {
  83                 s64 delay = (card->reset_jiffies + HZ) - get_jiffies_64();
  84                 if (delay <= 0)
  85                         return 0;
  86                 if (schedule_timeout_interruptible(delay) > 0)
  87                         return -ERESTARTSYS;
  88         }
  89 }
  90
  91 /**
  92  * fw_iso_resources_allocate - allocate isochronous channel and bandwidth
  93  * @r: the resource manager
  94  * @max_payload_bytes: the amount of data (including CIP headers) per packet
  95  * @speed: the speed (e.g., SCODE_400) at which the packets will be sent
  96  *
  97  * This function allocates one isochronous channel and enough bandwidth for the
  98  * specified packet size.
  99  *
 100  * Returns the channel number that the caller must use for streaming, or
 101  * a negative error code.  Due to potentionally long delays, this function is
 102  * interruptible and can return -ERESTARTSYS.  On success, the caller is
 103  * responsible for calling fw_iso_resources_update() on bus resets, and
 104  * fw_iso_resources_free() when the resources are not longer needed.
 105  */
 106 int fw_iso_resources_allocate(struct fw_iso_resources *r,
 107                               unsigned int max_payload_bytes, int speed)
 108 {
 109         struct fw_card *card = fw_parent_device(r->unit)->card;
 110         int bandwidth, channel, err;
 111
 112         if (WARN_ON(r->allocated))
 113                 return -EBADFD;
 114
 115         r->bandwidth = packet_bandwidth(max_payload_bytes, speed);
 116
 117 retry_after_bus_reset:
 118         spin_lock_irq(&card->lock);
 119         r->generation = card->generation;
 120         r->bandwidth_overhead = current_bandwidth_overhead(card);
 121         spin_unlock_irq(&card->lock);
 122
 123         err = wait_isoch_resource_delay_after_bus_reset(card);
 124         if (err < 0)
 125                 return err;
 126
 127         mutex_lock(&r->mutex);
 128
 129         bandwidth = r->bandwidth + r->bandwidth_overhead;
 130         fw_iso_resource_manage(card, r->generation, r->channels_mask,
 131                                &channel, &bandwidth, true);
 132         if (channel == -EAGAIN) {
 133                 mutex_unlock(&r->mutex);
 134                 goto retry_after_bus_reset;
 135         }
 136         if (channel >= 0) {
 137                 r->channel = channel;
 138                 r->allocated = true;
 139         } else {
 140                 if (channel == -EBUSY)
 141                         dev_err(&r->unit->device,
 142                                 "isochronous resources exhausted\n");
 143                 else
 144                         dev_err(&r->unit->device,
 145                                 "isochronous resource allocation failed\n");
 146         }
 147
 148         mutex_unlock(&r->mutex);
 149
 150         return channel;
 151 }
 152 EXPORT_SYMBOL(fw_iso_resources_allocate);
 153
 154 /**
 155  * fw_iso_resources_update - update resource allocations after a bus reset
 156  * @r: the resource manager
 157  *
 158  * This function must be called from the driver's .update handler to reallocate
 159  * any resources that were allocated before the bus reset.  It is safe to call
 160  * this function if no resources are currently allocated.
 161  *
 162  * Returns a negative error code on failure.  If this happens, the caller must
 163  * stop streaming.
 164  */
 165 int fw_iso_resources_update(struct fw_iso_resources *r)
 166 {
 167         struct fw_card *card = fw_parent_device(r->unit)->card;
 168         int bandwidth, channel;
 169
 170         mutex_lock(&r->mutex);
 171
 172         if (!r->allocated) {
 173                 mutex_unlock(&r->mutex);
 174                 return 0;
 175         }
 176
 177         spin_lock_irq(&card->lock);
 178         r->generation = card->generation;
 179         r->bandwidth_overhead = current_bandwidth_overhead(card);
 180         spin_unlock_irq(&card->lock);
 181
 182         bandwidth = r->bandwidth + r->bandwidth_overhead;
 183
 184         fw_iso_resource_manage(card, r->generation, 1uLL << r->channel,
 185                                &channel, &bandwidth, true);
 186         /*
 187          * When another bus reset happens, pretend that the allocation
 188          * succeeded; we will try again for the new generation later.
 189          */
 190         if (channel < 0 && channel != -EAGAIN) {
 191                 r->allocated = false;
 192                 if (channel == -EBUSY)
 193                         dev_err(&r->unit->device,
 194                                 "isochronous resources exhausted\n");
 195                 else
 196                         dev_err(&r->unit->device,
 197                                 "isochronous resource allocation failed\n");
 198         }
 199
 200         mutex_unlock(&r->mutex);
 201
 202         return channel;
 203 }
 204 EXPORT_SYMBOL(fw_iso_resources_update);
 205
 206 /**
 207  * fw_iso_resources_free - frees allocated resources
 208  * @r: the resource manager
 209  *
 210  * This function deallocates the channel and bandwidth, if allocated.
 211  */
 212 void fw_iso_resources_free(struct fw_iso_resources *r)
 213 {
 214         struct fw_card *card = fw_parent_device(r->unit)->card;
 215         int bandwidth, channel;
 216
 217         mutex_lock(&r->mutex);
 218
 219         if (r->allocated) {
 220                 bandwidth = r->bandwidth + r->bandwidth_overhead;
 221                 fw_iso_resource_manage(card, r->generation, 1uLL << r->channel,
 222                                        &channel, &bandwidth, false);
 223                 if (channel < 0)
 224                         dev_err(&r->unit->device,
 225                                 "isochronous resource deallocation failed\n");
 226
 227                 r->allocated = false;
 228         }
 229
 230         mutex_unlock(&r->mutex);
 231 }
 232 EXPORT_SYMBOL(fw_iso_resources_free);