linux-kernel - Re: [net PATCH v3 02/10] octeontx2-af: Fix start and end bit for scan config

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Date:   Wed, 19 Apr 2023 12:35:26 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     Sai Krishna <saikrishnag@...vell.com>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, leon@...nel.org,
        sgoutham@...vell.com, gakula@...vell.com, lcherian@...vell.com,
        jerinj@...vell.com, hkelam@...vell.com, sbhatta@...vell.com,
        Ratheesh Kannoth <rkannoth@...vell.com>
Subject: Re: [net PATCH v3 02/10] octeontx2-af: Fix start and end bit for
 scan config

On Wed, Apr 19, 2023 at 11:50:10AM +0530, Sai Krishna wrote:
> From: Ratheesh Kannoth <rkannoth@...vell.com>
> 
> Fix the NPC nibble start and end positions in the bit
> map. for_each_set_bit_from() needs start bit as one bit prior
> and end bit as one bit post position in the bit map
> 
> Fixes: b747923afff8 ("octeontx2-af: Exact match support")
> Signed-off-by: Ratheesh Kannoth <rkannoth@...vell.com>
> Signed-off-by: Sunil Kovvuri Goutham <sgoutham@...vell.com>
> Signed-off-by: Sai Krishna <saikrishnag@...vell.com>

I think it would be nice to explain why, and what effect this has.

Also, TBH, I'm unsure why the start needs to be one bit prior.

> ---
>  drivers/net/ethernet/marvell/octeontx2/af/rvu_npc_fs.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/octeontx2/af/rvu_npc_fs.c b/drivers/net/ethernet/marvell/octeontx2/af/rvu_npc_fs.c
> index 006beb5cf98d..27603078689a 100644
> --- a/drivers/net/ethernet/marvell/octeontx2/af/rvu_npc_fs.c
> +++ b/drivers/net/ethernet/marvell/octeontx2/af/rvu_npc_fs.c
> @@ -593,9 +593,8 @@ static int npc_scan_kex(struct rvu *rvu, int blkaddr, u8 intf)
>  	 * exact match code.
>  	 */
>  	masked_cfg = cfg & NPC_EXACT_NIBBLE;
> -	bitnr = NPC_EXACT_NIBBLE_START;
> -	for_each_set_bit_from(bitnr, (unsigned long *)&masked_cfg,
> -			      NPC_EXACT_NIBBLE_START) {
> +	bitnr = NPC_EXACT_NIBBLE_START - 1;
> +	for_each_set_bit_from(bitnr, (unsigned long *)&masked_cfg, NPC_EXACT_NIBBLE_END + 1) {
>  		npc_scan_exact_result(mcam, bitnr, key_nibble, intf);
>  		key_nibble++;
>  	}
> -- 
> 2.25.1
>