linux-kernel - RE: [patch V2 12/33] PCI/MSI: Add support for per device MSI[X] domains

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Date:   Thu, 24 Nov 2022 01:08:33 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
CC:     "x86@...nel.org" <x86@...nel.org>, Joerg Roedel <joro@...tes.org>,
        "Will Deacon" <will@...nel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Lorenzo Pieralisi" <lorenzo.pieralisi@....com>,
        Marc Zyngier <maz@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...lanox.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        "Raj, Ashok" <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
        Allen Hubbe <allenbh@...il.com>,
        "Ahmed S. Darwish" <darwi@...utronix.de>
Subject: RE: [patch V2 12/33] PCI/MSI: Add support for per device MSI[X]
 domains

> From: Thomas Gleixner <tglx@...utronix.de>
> Sent: Thursday, November 24, 2022 5:50 AM
> 
> >> This is general PCI MSI logic. So an open related to my rely to patch02,
> >> is it correct for PCI core to assume that the real parent imposes all the
> >> restrictions and there is no need to further go down the hierarchy?
> >
> > That was my working assumption and it turned out to be correct with both
> > x86 and ARM.
> 
> As a follow up, I went through some of the other architectures,
> especially the places which have extra limitations and it turns out that
> the restriction comes always from the direct parent.
> 
> If that ever changes then we need a callback which lets us evaluate the
> resulting capabilities through the hierarchy. That's nothing which can
> be evaluated directly.
> 
> Just look at the x86 hierarchy with IR. IR allows multi PCI-MSI, but the
> vector domain does not. Who is right? That's a decision which is made in
> the particular hierarchy.

make sense.

> 
> For now it's valid that the direct MSI parent has the proper set
> available.
> 

probably above can be marked out in the comment.