mac80211.c

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#include <linux/types.h>

#include "ath5k.h"
#include "mac80211.h"

static inline int ath5k_is_erp_rate(unsigned int mode, int rate)
{
        if (mode == AR5K_MODE_11G) {
                if (rate != 10 && rate != 20 &&
                    rate != 55 && rate != 110)
                        return 1;
        }
        return 0;
}

int ath5k_get_hdrlen(u16 fc)
{
        int hdrlen = 24;

        switch (fc & IEEE80211_FCTL_FTYPE) {
        case IEEE80211_FTYPE_DATA:
                if ((fc & IEEE80211_FCTL_FROMDS) && (fc & IEEE80211_FCTL_TODS))
                        hdrlen = 30; /* Addr4 */
                /*
                 * The QoS Control field is two bytes and its presence is
                 * indicated by the IEEE80211_STYPE_QOS_DATA bit. Add 2 to
                 * hdrlen if that bit is set.
                 * This works by masking out the bit and shifting it to
                 * bit position 1 so the result has the value 0 or 2.
                 */
                hdrlen += (fc & IEEE80211_STYPE_QOS_DATA) >> 6;
                break;
        case IEEE80211_FTYPE_CTL:
                /*
                 * ACK and CTS are 10 bytes, all others 16. To see how
                 * to get this condition consider
                 *   subtype mask:   0b0000000011110000 (0x00F0)
                 *   ACK subtype:    0b0000000011010000 (0x00D0)
                 *   CTS subtype:    0b0000000011000000 (0x00C0)
                 *   bits that matter:         ^^^      (0x00E0)
                 *   value of those: 0b0000000011000000 (0x00C0)
                 */
                if ((fc & 0xE0) == 0xC0)
                        hdrlen = 10;
                else
                        hdrlen = 16;
                break;
        }

        return hdrlen;
}

int ath5k_get_hdrlen_from_skb(const struct sk_buff *skb)
{
        const struct ieee80211_hdr *hdr = (const struct ieee80211_hdr *) skb->data;
        int hdrlen;

        if (unlikely(skb->len < 10))
                return 0;
        hdrlen = ath5k_get_hdrlen(le16_to_cpu(hdr->frame_control));
        if (unlikely(hdrlen > skb->len))
                return 0;
        return hdrlen;
}

int ath5k_frame_duration(unsigned int mode, size_t len,
                             int rate, int erp, int short_preamble)
{
        int dur;

        /* calculate duration (in microseconds, rounded up to next higher
         * integer if it includes a fractional microsecond) to send frame of
         * len bytes (does not include FCS) at the given rate. Duration will
         * also include SIFS.
         *
         * rate is in 100 kbps, so divident is multiplied by 10 in the
         * DIV_ROUND_UP() operations.
         */

        if (mode == AR5K_MODE_11A || erp) {
                /*
                 * OFDM:
                 *
                 * N_DBPS = DATARATE x 4
                 * N_SYM = Ceiling((16+8xLENGTH+6) / N_DBPS)
                 *      (16 = SIGNAL time, 6 = tail bits)
                 * TXTIME = T_PREAMBLE + T_SIGNAL + T_SYM x N_SYM + Signal Ext
                 *
                 * T_SYM = 4 usec
                 * 802.11a - 17.5.2: aSIFSTime = 16 usec
                 * 802.11g - 19.8.4: aSIFSTime = 10 usec +
                 *      signal ext = 6 usec
                 */
                dur = 16; /* SIFS + signal ext */
                dur += 16; /* 17.3.2.3: T_PREAMBLE = 16 usec */
                dur += 4; /* 17.3.2.3: T_SIGNAL = 4 usec */
                dur += 4 * DIV_ROUND_UP((16 + 8 * (len + 4) + 6) * 10,
                                        4 * rate); /* T_SYM x N_SYM */
        } else {
                /*
                 * 802.11b or 802.11g with 802.11b compatibility:
                 * 18.3.4: TXTIME = PreambleLength + PLCPHeaderTime +
                 * Ceiling(((LENGTH+PBCC)x8)/DATARATE). PBCC=0.
                 *
                 * 802.11 (DS): 15.3.3, 802.11b: 18.3.4
                 * aSIFSTime = 10 usec
                 * aPreambleLength = 144 usec or 72 usec with short preamble
                 * aPLCPHeaderLength = 48 usec or 24 usec with short preamble
                 */
                dur = 10; /* aSIFSTime = 10 usec */
                dur += short_preamble ? (72 + 24) : (144 + 48);

                dur += DIV_ROUND_UP(8 * (len + 4) * 10, rate);
        }

        return dur;
}

/* Exported duration function for driver use */
__le16 ath5k_generic_frame_duration(unsigned int mode,
                                                                                bool short_preamble,
                                        size_t frame_len, int rate)
{
        u16 dur;
        int erp;

        erp = ath5k_is_erp_rate(mode, rate);
        dur = ath5k_frame_duration(mode, frame_len, rate, erp, short_preamble);

        return cpu_to_le16(dur);
}

int ath5k_frequency_to_channel(int freq)
{
        if (freq == 2484)
                return 14;

        if (freq < 2484)
                return (freq - 2407) / 5;

        /* FIXME: 802.11j 17.3.8.3.2 */
        return freq/5 - 1000;
}