linux-kernel - Re: [PATCH] mac80211: Fix wrong channel bandwidths reported for aggregates

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Message-ID: <31e87fa2-6fea-5fe2-ab80-6050da9af7ce@simonwunderlich.de>
Date:   Tue, 19 Jul 2022 17:36:33 +0200
From:   Linus Lüssing <ll@...onwunderlich.de>
To:     Adrian Chadd <adrian@...ebsd.org>,
        Linus Lüssing <linus.luessing@...3.blue>
Cc:     Johannes Berg <johannes.berg@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Kalle Valo <kvalo@...nel.org>, Felix Fietkau <nbd@....name>,
        Simon Wunderlich <sw@...onwunderlich.de>,
        Sven Eckelmann <sven@...fation.org>,
        ath10k <ath10k@...ts.infradead.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mac80211: Fix wrong channel bandwidths reported for
 aggregates

On 19/07/2022 17:03, Adrian Chadd wrote:
> Hi!
> 
> It's not a hardware bug. Dating back to the original AR5416 11n chip,
> most flags aren't valid for subframes in an aggregate. Only the final
> frame has valid flags. This was explicitly covered internally way back
> when.

Ah, thanks for the clarification! I see it in the datasheet for the 
QCA9531, too, now. And thanks for the confirmation, that what we are 
doing so far is not correct for ath9k.

Words 0+2 are valid for all RX descriptors, 0+2+11 valid for the last RX 
descriptor of each packet and 0-11 for the last RX descriptor of an 
aggregate or last RX descriptor of a stand-alone packet. Or in other 
words, word 4, which contains the 20 vs. 40 MHz indicator, is invalid 
for any aggregate sub-frame other than the last one. I can rename that 
in the commit message.

Another approach that also came to my mind was introducing more explicit 
flags in cfg80211.h's "struct rate_info", like a RATE_INFO_BW_UNKNOWN in 
"enum rate_info_bw" and/or RATE_INFO_FLAGS_UNKNOWN in "enum 
rate_info_flags". And setting those flags in ath9k_cmn_process_rate().

The current approach is smaller though, as it simply uses the already 
existing flags. If anyone has any preferences, please let me know.

Regards, Linus