Luis R. Rodriguez | 13b8155 | 2009-09-10 17:52:45 -0700 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright (c) 2009 Atheros Communications Inc. |
| 3 | * |
| 4 | * Permission to use, copy, modify, and/or distribute this software for any |
| 5 | * purpose with or without fee is hereby granted, provided that the above |
| 6 | * copyright notice and this permission notice appear in all copies. |
| 7 | * |
| 8 | * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES |
| 9 | * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF |
| 10 | * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR |
| 11 | * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| 12 | * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN |
| 13 | * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF |
| 14 | * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. |
| 15 | */ |
| 16 | |
| 17 | #include <asm/unaligned.h> |
| 18 | |
| 19 | #include "ath.h" |
| 20 | #include "reg.h" |
| 21 | |
| 22 | #define REG_READ common->ops->read |
| 23 | #define REG_WRITE common->ops->write |
| 24 | |
| 25 | /** |
| 26 | * ath_hw_set_bssid_mask - filter out bssids we listen |
| 27 | * |
| 28 | * @common: the ath_common struct for the device. |
| 29 | * |
| 30 | * BSSID masking is a method used by AR5212 and newer hardware to inform PCU |
| 31 | * which bits of the interface's MAC address should be looked at when trying |
| 32 | * to decide which packets to ACK. In station mode and AP mode with a single |
| 33 | * BSS every bit matters since we lock to only one BSS. In AP mode with |
| 34 | * multiple BSSes (virtual interfaces) not every bit matters because hw must |
| 35 | * accept frames for all BSSes and so we tweak some bits of our mac address |
| 36 | * in order to have multiple BSSes. |
| 37 | * |
| 38 | * NOTE: This is a simple filter and does *not* filter out all |
| 39 | * relevant frames. Some frames that are not for us might get ACKed from us |
| 40 | * by PCU because they just match the mask. |
| 41 | * |
| 42 | * When handling multiple BSSes you can get the BSSID mask by computing the |
| 43 | * set of ~ ( MAC XOR BSSID ) for all bssids we handle. |
| 44 | * |
| 45 | * When you do this you are essentially computing the common bits of all your |
| 46 | * BSSes. Later it is assumed the harware will "and" (&) the BSSID mask with |
| 47 | * the MAC address to obtain the relevant bits and compare the result with |
| 48 | * (frame's BSSID & mask) to see if they match. |
| 49 | * |
| 50 | * Simple example: on your card you have have two BSSes you have created with |
| 51 | * BSSID-01 and BSSID-02. Lets assume BSSID-01 will not use the MAC address. |
| 52 | * There is another BSSID-03 but you are not part of it. For simplicity's sake, |
| 53 | * assuming only 4 bits for a mac address and for BSSIDs you can then have: |
| 54 | * |
| 55 | * \ |
| 56 | * MAC: 0001 | |
| 57 | * BSSID-01: 0100 | --> Belongs to us |
| 58 | * BSSID-02: 1001 | |
| 59 | * / |
| 60 | * ------------------- |
| 61 | * BSSID-03: 0110 | --> External |
| 62 | * ------------------- |
| 63 | * |
| 64 | * Our bssid_mask would then be: |
| 65 | * |
| 66 | * On loop iteration for BSSID-01: |
| 67 | * ~(0001 ^ 0100) -> ~(0101) |
| 68 | * -> 1010 |
| 69 | * bssid_mask = 1010 |
| 70 | * |
| 71 | * On loop iteration for BSSID-02: |
| 72 | * bssid_mask &= ~(0001 ^ 1001) |
| 73 | * bssid_mask = (1010) & ~(0001 ^ 1001) |
| 74 | * bssid_mask = (1010) & ~(1001) |
| 75 | * bssid_mask = (1010) & (0110) |
| 76 | * bssid_mask = 0010 |
| 77 | * |
| 78 | * A bssid_mask of 0010 means "only pay attention to the second least |
| 79 | * significant bit". This is because its the only bit common |
| 80 | * amongst the MAC and all BSSIDs we support. To findout what the real |
| 81 | * common bit is we can simply "&" the bssid_mask now with any BSSID we have |
| 82 | * or our MAC address (we assume the hardware uses the MAC address). |
| 83 | * |
| 84 | * Now, suppose there's an incoming frame for BSSID-03: |
| 85 | * |
| 86 | * IFRAME-01: 0110 |
| 87 | * |
| 88 | * An easy eye-inspeciton of this already should tell you that this frame |
| 89 | * will not pass our check. This is beacuse the bssid_mask tells the |
| 90 | * hardware to only look at the second least significant bit and the |
| 91 | * common bit amongst the MAC and BSSIDs is 0, this frame has the 2nd LSB |
| 92 | * as 1, which does not match 0. |
| 93 | * |
| 94 | * So with IFRAME-01 we *assume* the hardware will do: |
| 95 | * |
| 96 | * allow = (IFRAME-01 & bssid_mask) == (bssid_mask & MAC) ? 1 : 0; |
| 97 | * --> allow = (0110 & 0010) == (0010 & 0001) ? 1 : 0; |
| 98 | * --> allow = (0010) == 0000 ? 1 : 0; |
| 99 | * --> allow = 0 |
| 100 | * |
| 101 | * Lets now test a frame that should work: |
| 102 | * |
| 103 | * IFRAME-02: 0001 (we should allow) |
| 104 | * |
| 105 | * allow = (0001 & 1010) == 1010 |
| 106 | * |
| 107 | * allow = (IFRAME-02 & bssid_mask) == (bssid_mask & MAC) ? 1 : 0; |
| 108 | * --> allow = (0001 & 0010) == (0010 & 0001) ? 1 :0; |
| 109 | * --> allow = (0010) == (0010) |
| 110 | * --> allow = 1 |
| 111 | * |
| 112 | * Other examples: |
| 113 | * |
| 114 | * IFRAME-03: 0100 --> allowed |
| 115 | * IFRAME-04: 1001 --> allowed |
| 116 | * IFRAME-05: 1101 --> allowed but its not for us!!! |
| 117 | * |
| 118 | */ |
| 119 | void ath_hw_setbssidmask(struct ath_common *common) |
| 120 | { |
| 121 | void *ah = common->ah; |
| 122 | |
| 123 | REG_WRITE(ah, get_unaligned_le32(common->bssidmask), AR_BSSMSKL); |
| 124 | REG_WRITE(ah, get_unaligned_le16(common->bssidmask + 4), AR_BSSMSKU); |
| 125 | } |
| 126 | EXPORT_SYMBOL(ath_hw_setbssidmask); |