Re: [PATCH 1/2] mac80211: add A-MSDU tx support

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2016-02-18 at 19:39 +0100, Felix Fietkau wrote:
> Requires software tx queueing support. frag_list support (for zero-
> copy) is optional.

"optional" ;-)

> @@ -1751,6 +1754,7 @@ struct ieee80211_sta {
>  	bool mfp;
>  	u8 max_amsdu_subframes;
>  	u16 max_amsdu_len;
> +	u16 max_rc_amsdu_len;

I may have missed this, but I didn't see you initialize this to
something. I think that's probably a bad idea, since you've now created
a situation in which a driver wanting to use txq support needs to also
use minstrel or update this field...

Apart from that, I'm not sure that having a field here that works like
this is a good idea at all - all the other fields in the vicinity kinda
go from mac80211 to the driver, where here you have something that
potentially goes from the driver to mac80211. Perhaps we can find a
better way of doing this?

> + * @IEEE80211_HW_TX_AMSDU: Hardware (or driver) supports software
> aggregated
> + *	A-MSDU frames. Requires software tx queueing support.

Or at least document that it also requires integration with the
max_rc_amsdu_len thing.

> + * @max_tx_fragments: maximum fragments per (A-)MSDU.

"fragments" is a bit unclear - I guess this should refer to fraglist
length only? Or is it meant to apply as a limit to the sum of pieces in
the fraglist? I think that should be clarified.

> +	txq = sta->sta.txq[tid];
> +	if (!amsdu && txq)
> +		set_bit(IEEE80211_TXQ_NO_AMSDU, &to_txq_info(txq)-
> >flags);

Did you intentionally not clear this on aggregation stop?

> +	if (skb_headroom(skb) < sizeof(amsdu_hdr) ||
> skb_tailroom(skb) < 3) {
> +		I802_DEBUG_INC(local->tx_expand_skb_head);
> +
> +		if (pskb_expand_head(skb, sizeof(amsdu_hdr), 3,
> GFP_ATOMIC)) {

You should be able to precalculate the amount of padding needed based
on the length of the skb, so why statically use 3 here?

> +	if (skb_headroom(skb) < 8 || skb_tailroom(skb) < 3) {
> +		I802_DEBUG_INC(local->tx_expand_skb_head);
> +
> +		if (pskb_expand_head(skb, 8, 3, GFP_ATOMIC)) {

similarly here? Where does the 8 come from?

> @@ -2820,6 +2983,10 @@ static bool ieee80211_xmit_fast(struct
> ieee80211_sub_if_data *sdata,
>  
>  	ieee80211_tx_stats(dev, skb->len + extra_head);
>  
> +	if ((hdr->frame_control &
> cpu_to_le16(IEEE80211_STYPE_QOS_DATA)) &&
> +	    ieee80211_amsdu_aggregate(sdata, sta, fast_tx, skb))
> +		return true;

Only on xmit_fast?

johannes