Subject: Re: [PATCH net] net: enetc: correct the indexes of highest and 2nd highest TCs

From: Maciej Fijalkowski <[email-masked]>
Date: Tue, 6 Jun 2023 21:41:57 +0200

On Tue, Jun 06, 2023 at 04:46:18PM +0800, [email-masked] wrote:
> From: Wei Fang <[email-masked]>

if you are a sender then you could skip line above.

> 
> For ENETC hardware, the TCs are numbered from 0 to N-1, where N
> is the number of TCs. Numerically higher TC has higher priority.
> It's obvious that the highest priority TC index should be N-1 and
> the 2nd highest priority TC index should be N-2.
> However, the previous logic uses netdev_get_prio_tc_map() to get
> the indexes of highest priority and 2nd highest priority TCs, it
> does not make sense and is incorrect. It may get wrong indexes of
> the two TCs and make the CBS unconfigurable. e.g.
> $ tc qdisc add dev eno0 parent root handle 100: mqprio num_tc 6 \
> 	map 0 0 1 1 2 3 4 5 queues 1@0 1@1 1@2 1@3 2@4 2@6 hw 1
> $ tc qdisc replace dev eno0 parent 100:6 cbs idleslope 100000 \
> 	sendslope -900000 hicredit 12 locredit -113 offload 1
> $ Error: Specified device failed to setup cbs hardware offload.
>   ^^^^^

newlines between commit message and example output would improve
readability. tc commands are awful to read by themselves :P

Please describe in the commit message what is the actual fix.

> 
> Fixes: c431047c4efe ("enetc: add support Credit Based Shaper(CBS) for hardware offload")
> Signed-off-by: Wei Fang <[email-masked]>
> ---
>  drivers/net/ethernet/freescale/enetc/enetc_qos.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc_qos.c b/drivers/net/ethernet/freescale/enetc/enetc_qos.c
> index 83c27bbbc6ed..126007ab70f6 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc_qos.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc_qos.c
> @@ -181,8 +181,8 @@ int enetc_setup_tc_cbs(struct net_device *ndev, void *type_data)
>  	int bw_sum = 0;
>  	u8 bw;
>  
> -	prio_top = netdev_get_prio_tc_map(ndev, tc_nums - 1);
> -	prio_next = netdev_get_prio_tc_map(ndev, tc_nums - 2);
> +	prio_top = tc_nums - 1;
> +	prio_next = tc_nums - 2;
>  
>  	/* Support highest prio and second prio tc in cbs mode */
>  	if (tc != prio_top && tc != prio_next)
> -- 
> 2.25.1
> 
>