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SubjectRE: [v4 2/8] iommu, x86: Define new irte structure for VT-d Posted-Interrupts
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> -----Original Message-----
> From: Joerg Roedel [mailto:joro@8bytes.org]
> Sent: Monday, March 23, 2015 7:58 PM
> To: Wu, Feng
> Cc: dwmw2@infradead.org; jiang.liu@linux.intel.com;
> iommu@lists.linux-foundation.org; linux-kernel@vger.kernel.org
> Subject: Re: [v4 2/8] iommu, x86: Define new irte structure for VT-d
> Posted-Interrupts
>
> Hi Feng,
>
> On Mon, Feb 02, 2015 at 04:06:58PM +0800, Feng Wu wrote:
> > Add a new irte_pi structure for VT-d Posted-Interrupts.
> >
> > Signed-off-by: Feng Wu <feng.wu@intel.com>
> > Reviewed-by: Jiang Liu <jiang.liu@linux.intel.com>
> > Acked-by: David Woodhouse <David.Woodhouse@intel.com>
> > ---
> > include/linux/dmar.h | 32 ++++++++++++++++++++++++++++++++
> > 1 files changed, 32 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/dmar.h b/include/linux/dmar.h
> > index 8473756..c7f9cda 100644
> > --- a/include/linux/dmar.h
> > +++ b/include/linux/dmar.h
> > @@ -212,6 +212,38 @@ struct irte {
> > };
> > };
> >
> > +struct irte_pi {
>
> I think it is better to put this as a union into struct irte. It saves
> memory and unnecessary casting in later patches.

Thanks for the comments!

Do you mean doing it like the following?

struct irte {
union {
struct {
__u64 present : 1,
fpd : 1,
dst_mode : 1,
redir_hint : 1,
trigger_mode : 1,
dlvry_mode : 3,
avail : 4,
__reserved_1 : 4,
vector : 8,
__reserved_2 : 8,
dest_id : 32;
};
struct {
__u64 present : 1,
fpd : 1,
__reserved_1 : 6,
avail : 4,
__reserved_2 : 2,
urg : 1,
pst : 1,
vector : 8,
__reserved_3 : 14,
pda_l : 26;
};
__u64 low;
};

union {
struct {
__u64 sid : 16,
sq : 2,
svt : 2,
__reserved_3 : 44;
};
struct {
__u64 sid : 16,
sq : 2,
svt : 2,
__reserved_4 : 12,
pda_h : 32;
};
__u64 high;
};
};

In fact, I also intended to make these two defines as one, however, this code will get build
error ("duplicated member") with new version of GCC, such as, gcc 4.9.1. I cannot find a
good way to handle this gracefully, since I don't want to impact the existing usage of this
structure . Do you have any ideas about this? Thanks a lot!

Thanks,
Feng

>
>
> Joerg



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