Subject: Re: [net-next v4 01/15] net/mlx5: Fix compilation warning for 32-bit platform

From: Leon Romanovsky <[email-masked]>
Date: Tue, 15 Dec 2020 06:59:29 +0200

On Mon, Dec 14, 2020 at 02:31:25PM -0800, Alexander Duyck wrote:
> On Mon, Dec 14, 2020 at 1:49 PM Saeed Mahameed <[email-masked]> wrote:
> >
> > From: Parav Pandit <[email-masked]>
> >
> > MLX5_GENERAL_OBJECT_TYPES types bitfield is 64-bit field.
> >
> > Defining an enum for such bit fields on 32-bit platform results in below
> > warning.
> >
> > ./include/vdso/bits.h:7:26: warning: left shift count >= width of type [-Wshift-count-overflow]
> >                          ^
> > ./include/linux/mlx5/mlx5_ifc.h:10716:46: note: in expansion of macro ‘BIT’
> >  MLX5_HCA_CAP_GENERAL_OBJECT_TYPES_SAMPLER = BIT(0x20),
> >                                              ^~~
> > Use 32-bit friendly left shift.
> >
> > Fixes: 2a2970891647 ("net/mlx5: Add sample offload hardware bits and structures")
> > Signed-off-by: Parav Pandit <[email-masked]>
> > Reported-by: Stephen Rothwell <[email-masked]>
> > Signed-off-by: Leon Romanovsky <[email-masked]>
> > Signed-off-by: Saeed Mahameed <[email-masked]>
> > ---
> >  include/linux/mlx5/mlx5_ifc.h | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/mlx5/mlx5_ifc.h b/include/linux/mlx5/mlx5_ifc.h
> > index 0d6e287d614f..b9f15935dfe5 100644
> > --- a/include/linux/mlx5/mlx5_ifc.h
> > +++ b/include/linux/mlx5/mlx5_ifc.h
> > @@ -10711,9 +10711,9 @@ struct mlx5_ifc_affiliated_event_header_bits {
> >  };
> >
> >  enum {
> > -       MLX5_HCA_CAP_GENERAL_OBJECT_TYPES_ENCRYPTION_KEY = BIT(0xc),
> > -       MLX5_HCA_CAP_GENERAL_OBJECT_TYPES_IPSEC = BIT(0x13),
> > -       MLX5_HCA_CAP_GENERAL_OBJECT_TYPES_SAMPLER = BIT(0x20),
> > +       MLX5_HCA_CAP_GENERAL_OBJECT_TYPES_ENCRYPTION_KEY = 1ULL << 0xc,
> > +       MLX5_HCA_CAP_GENERAL_OBJECT_TYPES_IPSEC = 1ULL << 0x13,
> > +       MLX5_HCA_CAP_GENERAL_OBJECT_TYPES_SAMPLER = 1ULL << 0x20,
> >  };
>
> Why not just use BIT_ULL?

mlx5_ifc.h doesn't include bits.h on-purpose and there are "*.c" files
that include that ifc header file, but don't include bits.h either.

It can cause to build failures in random builds.

The mlx5_ifc.h is our main hardware definition file that we are using in
other projects outside of the kernel (rdma-core) too, so it is preferable
to keep it as plain-C without any extra dependencies.

Thanks