linux-kernel - Re: [PATCH net] net: dsa: felix: fix taprio guard band overflow at 10Mbps with jumbo frames

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Message-ID: <20230614121759.riazt6xiskk74h6r@skbuf>
Date:   Wed, 14 Jun 2023 15:17:59 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: felix: fix taprio guard band overflow at
 10Mbps with jumbo frames

On Wed, Jun 14, 2023 at 02:05:15PM +0200, Simon Horman wrote:
> Reviewed-by: Simon Horman <simon.horman@...igine.com>

Thanks.

> In a similar vein, you may want to consider the following suggestion from
> Coccinelle.
> 
>   .../felix_vsc9959.c:1382:2-8: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
>

Yeah, but there, there's an earlier restriction for cycle_time to never
exceed NSEC_PER_SEC (1000000000L) which fits on 32 bits.

Nonetheless, it is a good reminder that there are too many disjoint
places in the kernel already that open-code the logic to advance a
taprio base time. It would indeed be good to consolidate all of those
into a static inline function offered by include/net/pkt_sched.h, which
is also warning-free.