Re: [PATCH 1/2] cxl/pci: Add generic MSI-X/MSI irq support

[Ira Weiny]

On Thu, Nov 03, 2022 at 06:09:16PM +0000, Jonathan Cameron wrote:
> On Wed, 2 Nov 2022 17:18:33 -0700
> Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote:
> 
> > On Wed, 02 Nov 2022, Ira Weiny wrote:
> > 
> > >On Wed, Nov 02, 2022 at 10:15:24AM -0700, Davidlohr Bueso wrote:  
> > >> Most CXL features that can have irqs will normally use only the first 16,
> > >> with the exception of isolation (cxl 3.0), which per the spec is up to 32.  
> > >
> > >Dan, Dave, and I were discussing this and we agree.  For now the only things
> > >people are working on are within the first 16 so why not just request 16 as the
> > >max for now?  
> > 
> > It is a fair compromise, yes.
> 
> works for me.

I made what I thought would be a simple change to your patch and built this
into my series.

Unfortunately the following does not work with the current Qemu.

/*
 * NOTE: Currently all the functions which are enabled for CXL require their
 * vectors to be in the first 16.  Allocate this number as the min/max.
 */
#define CXL_PCI_REQUIRED_VECTORS 16

...

        rc = pci_alloc_irq_vectors(pdev, CXL_PCI_REQUIRED_VECTORS,            
                                   CXL_PCI_REQUIRED_VECTORS,
                                   PCI_IRQ_MSIX | PCI_IRQ_MSI);

This is because Qemu CXL devices only support (with the event changes I have
made) 8 msg numbers.  So the code fails to allocate any vectors.

I guess I should have known better.  But allocating something less than 16 I
guess needs to be allowed.

But that also means that beyond knowing _if_ irq's have been enabled I think
each CXL feature needs to know the number of vectors allocated so they can
ensure their msg numbers are going to work.

So how about the following as a diff to this patch?

In the event code I have then used the nr_irq_vecs field to determine if I
should enable the irq for each log.

If you are ok with it I'm going to squash it into your patch and send out a new
version of the event log series.

Thanks,
Ira