linux-kernel - Re: [PATCH] mthca: work around -Wenum-conversion warning

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Date:   Thu, 12 Nov 2020 17:45:00 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Doug Ledford <dledford@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mthca: work around -Wenum-conversion warning

On Thu, Nov 12, 2020 at 4:57 PM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Mon, Oct 26, 2020 at 10:12:30PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > gcc points out a suspicious mixing of enum types in a function that
> > converts from MTHCA_OPCODE_* values to IB_WC_* values:
> >
> > drivers/infiniband/hw/mthca/mthca_cq.c: In function 'mthca_poll_one':
> > drivers/infiniband/hw/mthca/mthca_cq.c:607:21: warning: implicit conversion from 'enum <anonymous>' to 'enum ib_wc_opcode' [-Wenum-conversion]
> >   607 |    entry->opcode    = MTHCA_OPCODE_INVALID;
> >
> > Nothing seems to ever check for MTHCA_OPCODE_INVALID again, no
> > idea if this is meaningful, but it seems harmless as it deals
> > with an invalid input.
> >
> > Add a cast to suppress the warning.
> >
> > Fixes: 2a4443a69934 ("[PATCH] IB/mthca: fill in opcode field for send completions")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> >  drivers/infiniband/hw/mthca/mthca_cq.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/infiniband/hw/mthca/mthca_cq.c b/drivers/infiniband/hw/mthca/mthca_cq.c
> > index c3cfea243af8..319b8aa63f36 100644
> > +++ b/drivers/infiniband/hw/mthca/mthca_cq.c
> > @@ -604,7 +604,7 @@ static inline int mthca_poll_one(struct mthca_dev *dev,
> >                       entry->byte_len  = MTHCA_ATOMIC_BYTE_LEN;
> >                       break;
> >               default:
> > -                     entry->opcode    = MTHCA_OPCODE_INVALID;
> > +                     entry->opcode    = (u8)MTHCA_OPCODE_INVALID;
> >                       break;
>
> This code is completely bogus, sigh
>
> Is this OK as far as the warning goes?

Yes, I'm sure your patch fixes it and it makes more sense than my version.

Acked-by: Arnd Bergmann <arnd@...db.de>