release/src-rt-6.x.4708/linux/linux-2.6.36/drivers/net/wireless/ath/hw.c

   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);