[rt2x00-users] [PATCH 5/5] rt2x00: Correctly identify MIMO_PS values

[Helmut Schaa]

Am Monday 23 August 2010 schrieb Ivo van Doorn:
> When sending frames, we should not use the STA capabilities
> to determine which MIMO PS settings should be applied. Instead
> we should read the configuration parameters from mac80211.
> Also the legacy drivers indicate that the MIMO PS static mode,
> have a maximum rate of MCS7.
> 
> Signed-off-by: Ivo van Doorn <IvDoorn at gmail.com>
> ---
>  drivers/net/wireless/rt2x00/rt2x00ht.c |   15 +++++++++------
>  1 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/wireless/rt2x00/rt2x00ht.c b/drivers/net/wireless/rt2x00/rt2x00ht.c
> index ad3c7ff..2e5d90e 100644
> --- a/drivers/net/wireless/rt2x00/rt2x00ht.c
> +++ b/drivers/net/wireless/rt2x00/rt2x00ht.c
> @@ -33,6 +33,7 @@ void rt2x00ht_create_tx_descriptor(struct queue_entry *entry,
>  				   struct txentry_desc *txdesc,
>  				   const struct rt2x00_rate *hwrate)
>  {
> +	struct ieee80211_hw *hw= entry->queue->rt2x00dev->hw;
>  	struct ieee80211_tx_info *tx_info = IEEE80211_SKB_CB(entry->skb);
>  	struct ieee80211_tx_rate *txrate = &tx_info->control.rates[0];
>  	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)entry->skb->data;
> @@ -57,13 +58,15 @@ void rt2x00ht_create_tx_descriptor(struct queue_entry *entry,
>  
>  		/*
>  		 * MIMO PS should be set to 1 for STA's using dynamic SM PS
> -		 * when using more then one tx stream (>MCS7).
> +		 * when using more then one tx stream (>MCS7). For Static
> +		 * SM PS does now allow MCS rates higher then 7.
>  		 */
> -		if (tx_info->control.sta && txdesc->mcs > 7 &&
> -		    (tx_info->control.sta->ht_cap.cap &
> -		     (WLAN_HT_CAP_SM_PS_DYNAMIC <<
> -		      IEEE80211_HT_CAP_SM_PS_SHIFT)))
> -			__set_bit(ENTRY_TXD_HT_MIMO_PS, &txdesc->flags);
> +		if (txdesc->mcs > 7) {
> +			if (hw->conf.smps_mode == IEEE80211_SMPS_DYNAMIC)
> +				__set_bit(ENTRY_TXD_HT_MIMO_PS, &txdesc->flags);
> +			else if (hw->conf.smps_mode == IEEE80211_SMPS_STATIC)
> +				txdesc->mcs = 7;
> +		}
>  	} else {
>  		txdesc->mcs = rt2x00_get_rate_mcs(hwrate->mcs);
>  		if (txrate->flags & IEEE80211_TX_RC_USE_SHORT_PREAMBLE)
> 

I agree with the mcs > 7 check for enabling MIMO_PS as it doesn't make sense to
enable it for MCS <= 7 rates. However, that could also be checked in mac80211.

The check for IEEE80211_SMPS_STATIC should also be accounted for in mac80211.
As long as we are in static smps mode mac80211 shouldn't try to send with mcs
rates requiring more chains then the enabled ones.

The check for IEEE80211_SMPS_DYNAMIC doesn't make sense I'd say. The previous
check was correct according to the spec sheet: "MMPS: 1: the remote peer is in
dynamic MIMO-PS mode".

So this bit should be set to 1 when the _remote peer_ is in dynamic MIMO PS
mode. The remote peer (be it the AP or a STA) is represented by
tx_info->control.sta and if the peer is in dynamic SMPS mode can be checked
with

tx_info->control.sta->ht_cap.cap &> (WLAN_HT_CAP_SM_PS_DYNAMIC << IEEE80211_HT_CAP_SM_PS_SHIFT)

So the current code should be correct.

Helmut