linux-kernel - Re: [RFC PATCHv3 3/4] x86/pci: Initial commit for new VMD device driver

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Message-ID: <alpine.DEB.2.11.1511041614070.4032@nanos>
Date:	Wed, 4 Nov 2015 16:14:50 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Keith Busch <keith.busch@...el.com>
cc:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	linux-pci@...r.kernel.org, Jiang Liu <jiang.liu@...ux.intel.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Bryan Veal <bryan.e.veal@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Martin Mares <mj@....cz>,
	Jon Derrick <jonathan.derrick@...el.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCHv3 3/4] x86/pci: Initial commit for new VMD device
 driver

On Wed, 4 Nov 2015, Keith Busch wrote:

> On Tue, Nov 03, 2015 at 12:42:02PM +0100, Thomas Gleixner wrote:
> > On Tue, 3 Nov 2015, Keith Busch wrote:
> > > > > +	msi_irqdomain = pci_msi_create_irq_domain(NULL, &pci_chained_msi_domain_info,
> > > > > +						  vmd_irqdomain);
> > 
> > But that parent limitation does not matter simply because your
> > msi_irqdomain does not follow down the hierarchy in the allocation
> > path.
> > 
> > So we can avoid the vmd_irqdomain creation completely. It's just
> > wasting memory and has no value at all. Creating the msi domain with a
> > NULL parent is possible.
> 
> I'm having trouble following the hierarchy and didn't understand the
> connection between the parent and msi comain. It's still new to me,
> but I don't think a NULL parent is allowable with msi domains:
> 
>  pci_msi_setup_msi_irqs()
>   pci_msi_domain_alloc_irqs()
>    msi_domain_alloc_irqs()
>     __irq_domain_alloc_irqs()
>      irq_domain_alloc_irqs_recursive()
>       msi_domain_alloc()
>        irq_domain_alloc_irqs_parent()
> 
> The last call returns -ENOSYS since there parent is NULL. Was the
> intension to allow no parent, or do I still need to allocate one to
> achieve the desired chaining?

Hmm, seems I missed that part. But that's a fixable problem. Jiang?

Thanks,

	tglx
 
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