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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@kernel.org>
To:     Jonas Jelonek <jelonek.jonas@gmail.com>,
        linux-wireless@vger.kernel.org
Cc:     thomas.huehn@hs-nordhausen.de, nbd@nbd.name, kvalo@kernel.org,
        johannes.berg@intel.com, lorenzo@kernel.org,
        Jonas Jelonek <jelonek.jonas@gmail.com>
Subject: Re: [PATCH] ath9k: fix per-packet TX-power cap for TPC
In-Reply-To: <20230330071854.757154-1-jelonek.jonas@gmail.com>
References: <20230330071854.757154-1-jelonek.jonas@gmail.com>
Date:   Thu, 30 Mar 2023 11:31:38 +0200
Message-ID: <87wn2ymvph.fsf@toke.dk>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Jonas Jelonek <jelonek.jonas@gmail.com> 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@gmail.com>

So what effect does this bug have in practice? Also, how did you test
the patch? :)

-Toke