linux-kernel - Re: [PATCH] mlxsw: spectrum_qdisc: Fix 64-bit division error in mlxsw_sp_qdisc_tbf_rate

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Date:   Thu, 30 Jan 2020 17:43:56 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Petr Machata <petrm@...lanox.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mlxsw: spectrum_qdisc: Fix 64-bit division error in
 mlxsw_sp_qdisc_tbf_rate_kbps

On 1/30/20 3:26 PM, Nathan Chancellor wrote:
> When building arm32 allmodconfig:
> 
> ERROR: "__aeabi_uldivmod"
> [drivers/net/ethernet/mellanox/mlxsw/mlxsw_spectrum.ko] undefined!
> 
> rate_bytes_ps has type u64, we need to use a 64-bit division helper to
> avoid a build error.
> 
> Fixes: a44f58c41bfb ("mlxsw: spectrum_qdisc: Support offloading of TBF Qdisc")
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
> index 79a2801d59f6..65e681ef01e8 100644
> --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
> +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_qdisc.c
> @@ -614,7 +614,7 @@ mlxsw_sp_qdisc_tbf_rate_kbps(struct tc_tbf_qopt_offload_replace_params *p)
>  	/* TBF interface is in bytes/s, whereas Spectrum ASIC is configured in
>  	 * Kbits/s.
>  	 */
> -	return p->rate.rate_bytes_ps / 1000 * 8;
> +	return div_u64(p->rate.rate_bytes_ps, 1000 * 8);

not quite right AFAICT.

try either
	return div_u64(p->rate.rate_bytes_ps * 8, 1000);
or
	return div_u64(p->rate.rate_bytes_ps, 1000) * 8;

>  }
>  
>  static int
> 


-- 
~Randy