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[1/2] mac80211: VHT off-by-one NSS

Message ID 1366038570-12457-1-git-send-email-karl.beldan@gmail.com (mailing list archive)
State Not Applicable, archived
Headers show

Commit Message

Karl Beldan April 15, 2013, 3:09 p.m. UTC 
From: Karl Beldan <karl.beldan@rivierawaves.com>

The number of VHT spatial streams (NSS) is found in:
- s8 ieee80211_tx_rate.rate.idx[6:4] (tx - filled by rate control)
- u8 ieee80211_rx_status.vht_nss     (rx - filled by driver)
Tx discriminates valid rates indexes with the sign bit and encodes NSS
starting from 0 to 7 (note this matches some hw encodings e.g IWLMVM).
Rx does not have the same constraints, and encodes NSS starting from 1
to 8 (note this matches what wireshark expects in the radiotap header).

To handle ieee80211_tx_rate.rate.idx[6:4] ieee80211_rate_set_vht() and
ieee80211_rate_get_vht_nss() assume their nss parameter and return value
respectively runs from 0 to 7.
ATM, there are only 2 users of these: cfg.c:sta_set_rate_info_t() and
iwlwifi/mvm/tx.c:iwl_mvm_hwrate_to_tx_control(), but both assume nss
runs from 1 to 8.
This patch fixes this inconsistency by making ieee80211_rate_set_vht()
and ieee80211_rate_get_vht_nss() handle an nss running from 1 to 8.

Signed-off-by: Karl Beldan <karl.beldan@rivierawaves.com>
---
This might feel very verbose for such a trivial thing.

 include/net/mac80211.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Johannes Berg April 16, 2013, 2:06 p.m. UTC | #1 
On Mon, 2013-04-15 at 17:09 +0200, Karl Beldan wrote:
> From: Karl Beldan <karl.beldan@rivierawaves.com>
> 
> The number of VHT spatial streams (NSS) is found in:
> - s8 ieee80211_tx_rate.rate.idx[6:4] (tx - filled by rate control)
> - u8 ieee80211_rx_status.vht_nss     (rx - filled by driver)
> Tx discriminates valid rates indexes with the sign bit and encodes NSS
> starting from 0 to 7 (note this matches some hw encodings e.g IWLMVM).
> Rx does not have the same constraints, and encodes NSS starting from 1
> to 8 (note this matches what wireshark expects in the radiotap header).
> 
> To handle ieee80211_tx_rate.rate.idx[6:4] ieee80211_rate_set_vht() and
> ieee80211_rate_get_vht_nss() assume their nss parameter and return value
> respectively runs from 0 to 7.
> ATM, there are only 2 users of these: cfg.c:sta_set_rate_info_t() and
> iwlwifi/mvm/tx.c:iwl_mvm_hwrate_to_tx_control(), but both assume nss
> runs from 1 to 8.
> This patch fixes this inconsistency by making ieee80211_rate_set_vht()
> and ieee80211_rate_get_vht_nss() handle an nss running from 1 to 8.
> 
> Signed-off-by: Karl Beldan <karl.beldan@rivierawaves.com>
> ---
> This might feel very verbose for such a trivial thing.

I think it's good, it's clearly a tricky area :-)

Applied both.

Btw, it seems we're missing VHT rates in net/mac80211/status.c, I was
wondering why that wasn't wrong but it's simply not there, heh. In fact
we probably mess it up when using VHT ...

johannes

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diff mbox

Patch

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 0dde213..2317ca9 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -601,8 +601,8 @@  static inline void ieee80211_rate_set_vht(struct ieee80211_tx_rate *rate,
 					  u8 mcs, u8 nss)
 {
 	WARN_ON(mcs & ~0xF);
-	WARN_ON(nss & ~0x7);
-	rate->idx = (nss << 4) | mcs;
+	WARN_ON((nss - 1) & ~0x7);
+	rate->idx = ((nss - 1) << 4) | mcs;
 }
 
 static inline u8
@@ -614,7 +614,7 @@  ieee80211_rate_get_vht_mcs(const struct ieee80211_tx_rate *rate)
 static inline u8
 ieee80211_rate_get_vht_nss(const struct ieee80211_tx_rate *rate)
 {
-	return rate->idx >> 4;
+	return (rate->idx >> 4) + 1;
 }
 
 /**