linux-kernel - [mt76/mt7603/mac] Question about missing variable assignment

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Date:   Sat, 2 Mar 2019 15:10:46 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Felix Fietkau <nbd@....name>,
        Lorenzo Bianconi <lorenzo.bianconi83@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [mt76/mt7603/mac] Question about missing variable assignment

Hi all,

The following piece of code in drivers/net/wireless/mediatek/mt76/mt7603/mac.c
is missing a variable assignment before line 1058.  Notice that there
is a potential execution path in which variable *i* is compared against
magic number 15 at line 1075 without being initialized previously
(this was reported by Coverity):

1055 out:
1056         final_rate_flags = info->status.rates[final_idx].flags;
1057 
1058         switch (FIELD_GET(MT_TX_RATE_MODE, final_rate)) {
1059         case MT_PHY_TYPE_CCK:
1060                 cck = true;
1061                 /* fall through */
1062         case MT_PHY_TYPE_OFDM:
1063                 if (dev->mt76.chandef.chan->band == NL80211_BAND_5GHZ)
1064                         sband = &dev->mt76.sband_5g.sband;
1065                 else
1066                         sband = &dev->mt76.sband_2g.sband;
1067                 final_rate &= GENMASK(5, 0);
1068                 final_rate = mt7603_get_rate(dev, sband, final_rate, cck);
1069                 final_rate_flags = 0;
1070                 break;
1071         case MT_PHY_TYPE_HT_GF:
1072         case MT_PHY_TYPE_HT:
1073                 final_rate_flags |= IEEE80211_TX_RC_MCS;
1074                 final_rate &= GENMASK(5, 0);
1075                 if (i > 15)
1076                         return false;
1077                 break;
1078         default:
1079                 return false;
1080         }

My guess is that such missing assignment should be something similar
to the one at line 566:

	i = FIELD_GET(MT_RXV1_TX_RATE, rxdg0);

but I'm not sure what the proper arguments for macro FIELD_GET should
be.

This code was introduced by commit c8846e1015022d2531ac4c895783e400b3e5babe

What do you think?

Thanks
--
Gustavo