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/*
* Copyright (c) 2009 Atheros Communications Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <asm/unaligned.h>
#include "ath.h"
#include "reg.h"
#define REG_READ common->ops->read
#define REG_WRITE common->ops->write
/**
* ath_hw_set_bssid_mask - filter out bssids we listen
*
* @common: the ath_common struct for the device.
*
* BSSID masking is a method used by AR5212 and newer hardware to inform PCU
* which bits of the interface's MAC address should be looked at when trying
* to decide which packets to ACK. In station mode and AP mode with a single
* BSS every bit matters since we lock to only one BSS. In AP mode with
* multiple BSSes (virtual interfaces) not every bit matters because hw must
* accept frames for all BSSes and so we tweak some bits of our mac address
* in order to have multiple BSSes.
*
* NOTE: This is a simple filter and does *not* filter out all
* relevant frames. Some frames that are not for us might get ACKed from us
* by PCU because they just match the mask.
*
* When handling multiple BSSes you can get the BSSID mask by computing the
* set of ~ ( MAC XOR BSSID ) for all bssids we handle.
*
* When you do this you are essentially computing the common bits of all your
* BSSes. Later it is assumed the harware will "and" (&) the BSSID mask with
* the MAC address to obtain the relevant bits and compare the result with
* (frame's BSSID & mask) to see if they match.
*
* Simple example: on your card you have have two BSSes you have created with
* BSSID-01 and BSSID-02. Lets assume BSSID-01 will not use the MAC address.
* There is another BSSID-03 but you are not part of it. For simplicity's sake,
* assuming only 4 bits for a mac address and for BSSIDs you can then have:
*
* \
* MAC: 0001 |
* BSSID-01: 0100 | --> Belongs to us
* BSSID-02: 1001 |
* /
* -------------------
* BSSID-03: 0110 | --> External
* -------------------
*
* Our bssid_mask would then be:
*
* On loop iteration for BSSID-01:
* ~(0001 ^ 0100) -> ~(0101)
* -> 1010
* bssid_mask = 1010
*
* On loop iteration for BSSID-02:
* bssid_mask &= ~(0001 ^ 1001)
* bssid_mask = (1010) & ~(0001 ^ 1001)
* bssid_mask = (1010) & ~(1001)
* bssid_mask = (1010) & (0110)
* bssid_mask = 0010
*
* A bssid_mask of 0010 means "only pay attention to the second least
* significant bit". This is because its the only bit common
* amongst the MAC and all BSSIDs we support. To findout what the real
* common bit is we can simply "&" the bssid_mask now with any BSSID we have
* or our MAC address (we assume the hardware uses the MAC address).
*
* Now, suppose there's an incoming frame for BSSID-03:
*
* IFRAME-01: 0110
*
* An easy eye-inspeciton of this already should tell you that this frame
* will not pass our check. This is beacuse the bssid_mask tells the
* hardware to only look at the second least significant bit and the
* common bit amongst the MAC and BSSIDs is 0, this frame has the 2nd LSB
* as 1, which does not match 0.
*
* So with IFRAME-01 we *assume* the hardware will do:
*
* allow = (IFRAME-01 & bssid_mask) == (bssid_mask & MAC) ? 1 : 0;
* --> allow = (0110 & 0010) == (0010 & 0001) ? 1 : 0;
* --> allow = (0010) == 0000 ? 1 : 0;
* --> allow = 0
*
* Lets now test a frame that should work:
*
* IFRAME-02: 0001 (we should allow)
*
* allow = (0001 & 1010) == 1010
*
* allow = (IFRAME-02 & bssid_mask) == (bssid_mask & MAC) ? 1 : 0;
* --> allow = (0001 & 0010) == (0010 & 0001) ? 1 :0;
* --> allow = (0010) == (0010)
* --> allow = 1
*
* Other examples:
*
* IFRAME-03: 0100 --> allowed
* IFRAME-04: 1001 --> allowed
* IFRAME-05: 1101 --> allowed but its not for us!!!
*
*/
void ath_hw_setbssidmask(struct ath_common *common)
{
void *ah = common->ah;
REG_WRITE(ah, get_unaligned_le32(common->bssidmask), AR_BSSMSKL);
REG_WRITE(ah, get_unaligned_le16(common->bssidmask + 4), AR_BSSMSKU);
}
EXPORT_SYMBOL(ath_hw_setbssidmask);
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