Re: [PATCH net-next v8 2/3] net: airoha: fix ETS QoS stats counter underflow and cross-channel corruption

[Simon Horman <horms@kernel.org>]

On Fri, Jul 03, 2026 at 11:19:26AM +0200, Lorenzo Bianconi wrote:
> airoha_qdma_get_tx_ets_stats() has two bugs:
> - The hardware counters read via airoha_qdma_rr() are 32-bit values
>   but are stored in u64 locals and subtracted from u64 baselines. When
>   a 32-bit hardware counter wraps around, the subtraction produces a
>   large underflow value passed to _bstats_update().
> - The baseline counters (cpu_tx_packets, fwd_tx_packets) are stored as
>   single per-device fields, but airoha_qdma_get_tx_ets_stats() is
>   called with different channel values (0-3). Each call reads a
>   different channel's hardware counter but overwrites the same
>   baseline, corrupting the delta computation for other channels.
> 
> Fix both by:
> - Narrowing the counter locals and baselines to u32 so that 32-bit
>   unsigned subtraction handles wrap-around naturally.
> - Grouping the baselines into a per-channel qos_stats array so each
>   channel tracks its own previous counter value independently.
> - Splitting the delta addition into two statements so the first u32
>   delta is widened to u64 on assignment and the second is added in
>   u64 arithmetic, preventing overflow when both deltas are large.
> 
> Fixes: 20bf7d07c956 ("net: airoha: Add sched ETS offload support")
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>

Reviewed-by: Simon Horman <horms@kernel.org>