Re: [PATCH] mlxsw: spectrum_qdisc: Fix 64-bit division error in mlxsw_sp_qdisc_tbf_rate_kbps

Nathan Chancellor
2020-01-31T01:48:25Z

On Thu, Jan 30, 2020 at 05:43:56PM -0800, Randy Dunlap wrote:
> 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@gmail.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;
>

Gah, I swear I can math... Thank you for catching this, v2 incoming with
the later because I think it looks better.

Cheers,
Nathan

> > }
> >
> > static int
> >
>
>
> --
> ~Randy
>