Re: PCIE

[Manu Abraham <abraham.manu@gmail.com>]

David Miller wrote:
> From: "H. Peter Anvin" <hpa@zytor.com>
> Date: Sat, 26 May 2007 19:34:26 -0700
> 
>> There are systems which only get a single bit indication that an MSI has
>> happened.
>>
>> Presumably we need something like IRQF_MSI which can be set as
>> appropriate depending on the architecture?
> 
> Although I don't want to make the IRQ handling subsystems any more
> complicated than they already are, one idea I floated around is that
> we could seperate CPU irq numbers (the things we pass around today)
> and MSI vector numbers.
> 
> But I immediately understand how that is unnecessary to some extent,
> any platform which needs to deal with that kind of distinction can use
> virtual IRQ numbers like sparc64 and powerpc do.
> 
> Sparc64 PCI-E controllers, for example, allow you to group several
> MSIs into a 'group', and the interrupt source is for the group rather
> than the individual MSIs.  When the MSI group interrupt arrives, you
> get a descriptor in a per-MSI-group ring buffer that describes the MSI
> that arrived.
> 
> This descriptor in fact passes on a ton of interesting information,
> see arch/sparc64/kernel/pci_sun4v.c:pci_sun4v_msiq_entry.
> 
> It gives you the type, the system TSC value at the time of interrupt
> arrival (so you could do incredibly cool profiling with this),
> the PCI bus/device/fn that generated the MSI vector, the MSI address
> that was signalled, the MSI data field, and full information for PCI-E
> MSG packets including bus/dev/fn of target, the message routing code,
> and the message code.
> 
> But we use none of these facilities currently because it's either
> impossible or too cumbersome to be useful at the moment.
> 

I think it is better to use IRQF_MSI as HPA suggested, since IRQF_SHARED
is a bit confusing thing altogether since MSI doesn't share interrupts.