xref: /linux/drivers/infiniband/hw/cxgb4/id_table.c (revision a4eb44a6435d6d8f9e642407a4a06f65eb90ca04)
1 /*
2  * Copyright (c) 2011 Chelsio Communications.  All rights reserved.
3  *
4  * This software is available to you under a choice of one of two
5  * licenses.  You may choose to be licensed under the terms of the GNU
6  * General Public License (GPL) Version 2, available from the file
7  * COPYING in the main directory of this source tree, or the
8  * OpenIB.org BSD license below:
9  *
10  *     Redistribution and use in source and binary forms, with or
11  *     without modification, are permitted provided that the following
12  *     conditions are met:
13  *
14  *      - Redistributions of source code must retain the above
15  *        copyright notice, this list of conditions and the following
16  *        disclaimer.
17  *
18  *      - Redistributions in binary form must reproduce the above
19  *        copyright notice, this list of conditions and the following
20  *        disclaimer in the documentation and/or other materials
21  *        provided with the distribution.
22  *
23  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
24  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
25  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
26  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
27  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
28  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
29  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
30  * SOFTWARE.
31  */
32 #include <linux/kernel.h>
33 #include <linux/random.h>
34 #include "iw_cxgb4.h"
35 
36 #define RANDOM_SKIP 16
37 
38 /*
39  * Trivial bitmap-based allocator. If the random flag is set, the
40  * allocator is designed to:
41  * - pseudo-randomize the id returned such that it is not trivially predictable.
42  * - avoid reuse of recently used id (at the expense of predictability)
43  */
44 u32 c4iw_id_alloc(struct c4iw_id_table *alloc)
45 {
46 	unsigned long flags;
47 	u32 obj;
48 
49 	spin_lock_irqsave(&alloc->lock, flags);
50 
51 	obj = find_next_zero_bit(alloc->table, alloc->max, alloc->last);
52 	if (obj >= alloc->max)
53 		obj = find_first_zero_bit(alloc->table, alloc->max);
54 
55 	if (obj < alloc->max) {
56 		if (alloc->flags & C4IW_ID_TABLE_F_RANDOM)
57 			alloc->last += prandom_u32() % RANDOM_SKIP;
58 		else
59 			alloc->last = obj + 1;
60 		if (alloc->last >= alloc->max)
61 			alloc->last = 0;
62 		__set_bit(obj, alloc->table);
63 		obj += alloc->start;
64 	} else
65 		obj = -1;
66 
67 	spin_unlock_irqrestore(&alloc->lock, flags);
68 	return obj;
69 }
70 
71 void c4iw_id_free(struct c4iw_id_table *alloc, u32 obj)
72 {
73 	unsigned long flags;
74 
75 	obj -= alloc->start;
76 
77 	spin_lock_irqsave(&alloc->lock, flags);
78 	__clear_bit(obj, alloc->table);
79 	spin_unlock_irqrestore(&alloc->lock, flags);
80 }
81 
82 int c4iw_id_table_alloc(struct c4iw_id_table *alloc, u32 start, u32 num,
83 			u32 reserved, u32 flags)
84 {
85 	alloc->start = start;
86 	alloc->flags = flags;
87 	if (flags & C4IW_ID_TABLE_F_RANDOM)
88 		alloc->last = prandom_u32() % RANDOM_SKIP;
89 	else
90 		alloc->last = 0;
91 	alloc->max = num;
92 	spin_lock_init(&alloc->lock);
93 	alloc->table = bitmap_zalloc(num, GFP_KERNEL);
94 	if (!alloc->table)
95 		return -ENOMEM;
96 
97 	if (!(alloc->flags & C4IW_ID_TABLE_F_EMPTY))
98 		bitmap_set(alloc->table, 0, reserved);
99 
100 	return 0;
101 }
102 
103 void c4iw_id_table_free(struct c4iw_id_table *alloc)
104 {
105 	bitmap_free(alloc->table);
106 }
107