Re: [PATCH 2/2] mac80211: minstrel_ht: do not sample unsupported rates

[Felix Fietkau <nbd@openwrt.org>]

On 2013-11-08 17:34, Karl Beldan wrote:
> From: Karl Beldan <karl.beldan@rivierawaves.com>
> 
> ATM minstrel_ht does not check whether the sampling rate is supported.
> Unsupported rates attempts can trigger when there are holes between
> supported MCSes belonging to the same group (e.g many devices are
> capable of MCS32 without being capable of MCS33->MCS39).
> This change replaces an unsupported sample index with the fls of the
> bitfield of supported indexes.
> This is not a problem in minstrel which fills a per STA sample table
> with only supported rates (though only at init).
> 
> Signed-off-by: Karl Beldan <karl.beldan@rivierawaves.com>
> ---
>  net/mac80211/rc80211_minstrel_ht.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
> index aeec401..1b835ad 100644
> --- a/net/mac80211/rc80211_minstrel_ht.c
> +++ b/net/mac80211/rc80211_minstrel_ht.c
> @@ -703,6 +703,8 @@ minstrel_get_sample_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
>  
>  	mg = &mi->groups[mi->sample_group];
>  	sample_idx = sample_table[mg->column][mg->index];
> +	if (!(mg->supported & BIT(sample_idx)))
> +		sample_idx = fls(sample_idx) - 1;
You probably meant fls(mg->supported) - 1 here, however I think a better
approach would be to just skip the sample attempt. If there are fewer
rates in a group, we can run fewer sample attempts on it.

- Felix