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