> On 30. Mar 2023, at 11:31, Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > Jonas Jelonek <jelonek.jonas@xxxxxxxxx> writes: > >> Fix incorrect usage of plain rate_idx as index into the max (power) per >> rate lookup table. >> >> For transmit power control (TPC), the ath9k driver maintains internal >> tables (in struct ath_hw) to store the max allowed power level per rate. >> They are used to limit a given TX-power according to regulatory and user >> limits in the TX-path per packet. The tables are filled in a predefined >> order, starting with values for CCK + OFDM rates and followed by the >> values for MCS rates. Thus, the maximum power levels for MCS do not >> start at index 0 in the table but are shifted by a fixed value. >> >> The TX-power limiting in ath_get_rate_txpower did not apply this shift, >> thus retrieved the incorrect maximum power level. For example, the >> maximum power for OFDM rate 0 was used for MCS rate 0. If STBC was used, >> the power was mostly limited to 0 because the STBC table is zeroed for >> legacy CCK/OFDM rates. This patch fixes this table lookup. >> >> Signed-off-by: Jonas Jelonek <jelonek.jonas@xxxxxxxxx> > > So what effect does this bug have in practice? Also, how did you test > the patch? :) > It actually may not have an effect in most of current practical applications. The member ‘tpc_enabled' in struct ath_hw is by default set to false and thus, TPC in ath9k is usually disabled. The code path will be skipped in that case. But it has an effect as I am still working on TPC per packet in ath9k as part of research. Looking at my traces I saw that the TX-power is capped at 0 for MCS rates 0-7 in case the STBC flag is set in struct ieee80211_tx_info. Thus, transmission was significantly worse as usual, and I also was not able to manually set a proper TX-power via my testing API. With other rates it is working fine. I also double-checked that it isn’t a problem of how TX-power is set and reported with our upcoming API. I tested this with my OpenWrt-based AP-STA desk setup using two different ath9k wifi chips (AR9280, AR9580), Kernel 5.15.98. I guess that should be sufficient as ath9k hasn’t changed that significantly since that and several changes are already backported. I compile-tested it with latest 6.3 kernel (+allyesconfig), the patch applied flawlessly and encountered no problems. After applying my patch, I could see that everything was working as expected. Transmission performs equally as if TPC was disabled, and setting + reporting TX-power was working again. Also verified this with some verbose debugging in ath_get_rate_txpower to see which index + max power is used. Jonas
