linux-kernel - Re: [PATCH] thunderbolt: Make priority unsigned in struct tb

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Date:   Wed, 24 Apr 2019 12:00:05 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] thunderbolt: Make priority unsigned in struct tb_path

On Wed, Apr 24, 2019 at 11:49:37AM -0700, Nick Desaulniers wrote:
> On Wed, Apr 24, 2019 at 11:34 AM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > Clang warns:
> >
> > drivers/thunderbolt/tunnel.c:504:17: warning: implicit truncation from
> > 'int' to bit-field changes value from 5 to -3
> > [-Wbitfield-constant-conversion]
> >         path->priority = 5;
> >                        ^ ~
> > 1 warning generated.
> >
> > The priority member in struct tb_path is only ever assigned a positive
> > number:
> >
> > $ rg -n priority drivers/thunderbolt/path.c
> > drivers/thunderbolt/tunnel.c:99:        path->priority = 3;
> > drivers/thunderbolt/tunnel.c:308:       path->priority = 2;
> > drivers/thunderbolt/tunnel.c:323:       path->priority = 1;
> > drivers/thunderbolt/tunnel.c:504:       path->priority = 5;
> 
> LGTM.  Looks like drivers/thunderbolt/tb_regs.h also defines it as u32
> (no change needed here).
> Triple checking it's uses, looks like it gets assigned:
> drivers/thunderbolt/path.c#L492:
> hop.priority = path->priority;
> hop is an instance of a struct tb_regs_hop, which is the definition I
> was looking at above.  LGTM thanks Nathan!
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

Thanks for the review!

> 
> >
> > Furthmore, that value is only assigned to an unsigned integer in

Although apparently I can't spell... should be "Furthermore".

> > tb_path_activate (the priority member in struct tb_regs_hop).
> >
> > Fixes: 44242d6c9703 ("thunderbolt: Add support for DMA tunnels")
> > Link: https://github.com/ClangBuiltLinux/linux/issues/454
> > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> > ---
> >  drivers/thunderbolt/tb.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
> > index 15d225dcb403..b12c8f33d89c 100644
> > --- a/drivers/thunderbolt/tb.h
> > +++ b/drivers/thunderbolt/tb.h
> > @@ -225,7 +225,7 @@ struct tb_path {
> >         enum tb_path_port ingress_fc_enable;
> >         enum tb_path_port egress_fc_enable;
> >
> > -       int priority:3;
> > +       unsigned int priority:3;
> >         int weight:4;
> >         bool drop_packages;
> >         bool activated;
> > --
> > 2.21.0
> >
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers