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Re: [Xen-devel] [PATCH v4 05/17] xen/arm: ITS: implement hw_irq_controller for LPIs

On Sat, 2015-07-18 at 11:13 +0100, Julien Grall wrote:
> Hi Ian,
> On 15/07/2015 10:32, Ian Campbell wrote:
> >> and save 2 byte if not more with the alignment per irq_desc.
> >
> > If this is a concern then I would say we would either want a separate
> > array of per-pLPI information which we do not want in irq_desc because
> > it is irq specific, or do add a pointer to its_desc which points to an
> > array of per-event information.
> I noticed that we have a field msi_desc in the structure irq_desc. On 
> ARM, the structure msi_desc is not defined at all but still waste a 8 
> byte for the pointer in the irq_desc.
> Given that LPI is an MSI, I'm wondering if we could move all LPI related 
> data in this msi_desc. This would avoid to introduce new field in the 
> irq_desc structure.

Yes, I think I suggested something similar at some point, although I
seemed to think msi_desc was more similar to its_device.

Looking at the content of the struct, alloc_msi_entry and
msi_capability_init makes me less sure, it looks like msi_entry on x86
is allocated as an array (sized for events) stored per device, which
doesn't directly map onto how ARM is structured.

So I think you suggestion may make more sense.

> The msi_desc would look like:
> struct msi_desc
> {
>       its_device *dev;
>       unsigned int eventID;
> };
> Regards,

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