wifi: mt76: mt7996: guard tx_retries against TXFREE count=0#1069
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wifi: mt76: mt7996: guard tx_retries against TXFREE count=0#1069rchen14b wants to merge 1 commit intoopenwrt:masterfrom
rchen14b wants to merge 1 commit intoopenwrt:masterfrom
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In mt7996_mac_tx_free(), the tx_retries calculation unconditionally subtracts 1 from the MT_TXFREE_INFO_COUNT field. When the count is 0, which occurs with NPU/WED WiFi offload (offloaded packets don't always generate TXFREE entries with valid counts), this causes an unsigned integer underflow producing bogus values like 4294967295. These corrupted counters accumulate in wcid->stats.tx_retries and propagate to userspace via iw station dump, making retry statistics meaningless when NPU offload is active. Fix by extracting the count into a local variable and checking it before the subtraction. Signed-off-by: Ryan Chen <rchen14b@gmail.com>
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In mt7996_mac_tx_free(), tx_retries is calculated as
FIELD_GET(MT_TXFREE_INFO_COUNT, info) - 1. When count is 0 (which
happens with NPU/WED WiFi offload), this underflows to ~4 billion
and corrupts wcid->stats.tx_retries.
Fix by checking count before subtracting.
Seen on Airoha AN7581 with NPU WiFi offload active — iw station dump
shows bogus retry counts in the billions. Same issue would affect any
mt7996 device using WED offload where TXFREE entries arrive with
count=0.