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