Re: [ath9k-devel] Override Minstrel HT RC to set an MCS bitrate (mask)

[Mohammed Shafi <shafi.ath9k@gmail.com>]

On Tue, Mar 8, 2011 at 11:10 PM, M. A. <jdiq123@googlemail.com> wrote:
> Hi all,
>
> My question is how can I modify Minstrel HT rate control to be able to
> override it (by a boolean or otherwise) to select an MCS or specific
> rate index from user space (such that once set it driver will only try
> sending at that rate until unset then driver will resort back to
> Minstrel RC).

I don't think we can fix the MCS rate index from user space, may be we
need a hack.
iw  dev <devname> set bitrates [legacy-<2.4|5> <legacy rate in Mbps>*]
and this is only for legacy rates.


>
> I have been able to change other kernel parameters at runtime(echo
> /sys/kernel/debug/ieee80211/...) by passing them through (fops) to
> DebugFs. however I am unsure of what parameters to pass through in the
> case of MCS rate fixing and what modifications to the code are
> required to achieve this.

don't know and I am not sure whether this can be easily done.

>
>
> Also I have been told that these sections of code facilitate the
> masking of rates;
>
> =========================================================================
> include/net/cfg80211.h: cfg80211_bitrate_mask
> -------------------------------------------------------------------------------------------------------
> /*
>  * cfg80211_bitrate_mask - masks for bitrate control
>  */
> struct cfg80211_bitrate_mask {
>        struct {
>                u32 legacy;
>                /* TODO: add support for masking MCS rates; e.g.: */
>                /* u8 mcs[IEEE80211_HT_MCS_MASK_LEN]; */
>        } control[IEEE80211_NUM_BANDS];
> };
> -------------------------------------------------------------------------------------------------------
> net/mac80211/cfg.c ieee80211_set_bitrate_mask
> -------------------------------------------------------------------------------------------------------
> static int ieee80211_set_bitrate_mask(struct wiphy *wiphy,
>                                      struct net_device *dev,
>                                      const u8 *addr,
>                                      const struct cfg80211_bitrate_mask *mask)
> {
>        struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
>        struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
>        int i;
>
>        /*
>         * This _could_ be supported by providing a hook for
>         * drivers for this function, but at this point it
>         * doesn't seem worth bothering.
>         */
>        if (local->hw.flags & IEEE80211_HW_HAS_RATE_CONTROL)
>                return -EOPNOTSUPP;
>
>
>        for (i = 0; i < IEEE80211_NUM_BANDS; i++)
>                sdata->rc_rateidx_mask[i] = mask->control[i].legacy;
>
>        return 0;
> }
> -------------------------------------------------------------------------------------------------------
> net/wireless/nl80211.c: nl80211_set_tx_bitrate_mask
> -------------------------------------------------------------------------------------------------------
> static int nl80211_set_tx_bitrate_mask(struct sk_buff *skb,
>                                       struct genl_info *info)
> {
>        struct nlattr *tb[NL80211_TXRATE_MAX + 1];
>        struct cfg80211_registered_device *rdev = info->user_ptr[0];
>        struct cfg80211_bitrate_mask mask;
>        int rem, i;
>        struct net_device *dev = info->user_ptr[1];
>        struct nlattr *tx_rates;
>        struct ieee80211_supported_band *sband;
>
>        if (info->attrs[NL80211_ATTR_TX_RATES] == NULL)
>                return -EINVAL;
>
>        if (!rdev->ops->set_bitrate_mask)
>                return -EOPNOTSUPP;
>
>        memset(&mask, 0, sizeof(mask));
>        /* Default to all rates enabled */
>        for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
>                sband = rdev->wiphy.bands[i];
>                mask.control[i].legacy =
>                        sband ? (1 << sband->n_bitrates) - 1 : 0;
>        }
>
>        /*
>         * The nested attribute uses enum nl80211_band as the index. This maps
>         * directly to the enum ieee80211_band values used in cfg80211.
>         */
>        nla_for_each_nested(tx_rates, info->attrs[NL80211_ATTR_TX_RATES], rem)
>        {
>                enum ieee80211_band band = nla_type(tx_rates);
>                if (band < 0 || band >= IEEE80211_NUM_BANDS)
>                        return -EINVAL;
>                sband = rdev->wiphy.bands[band];
>                if (sband == NULL)
>                        return -EINVAL;
>                nla_parse(tb, NL80211_TXRATE_MAX, nla_data(tx_rates),
>                          nla_len(tx_rates), nl80211_txattr_policy);
>                if (tb[NL80211_TXRATE_LEGACY]) {
>                        mask.control[band].legacy = rateset_to_mask(
>                                sband,
>                                nla_data(tb[NL80211_TXRATE_LEGACY]),
>                                nla_len(tb[NL80211_TXRATE_LEGACY]));
>                        if (mask.control[band].legacy == 0)
>                                return -EINVAL;
>                }
>        }
>
>        return rdev->ops->set_bitrate_mask(&rdev->wiphy, dev, NULL, &mask);
> }

As you see everything is for legacy thing and for MCS it's a TODO section.

> ====================================================================================================================
>
>
> Any help is much appreciated!
>
> Thank you all very much
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