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

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Message-ID: <Y3V+u+h7jGbRj3cE@nvidia.com>
Date:   Wed, 16 Nov 2022 20:22:19 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.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>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Ashok Raj <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
        Allen Hubbe <allenbh@...il.com>,
        "Ahmed S. Darwish" <darwi@...utronix.de>,
        Reinette Chatre <reinette.chatre@...el.com>
Subject: Re: [patch 12/33] PCI/MSI: Add support for per device MSI[X] domains

On Wed, Nov 16, 2022 at 11:38:52PM +0100, Thomas Gleixner wrote:

> >> +bool pci_setup_msi_device_domain(struct pci_dev *pdev)
> >> +{
> >> +	if (WARN_ON_ONCE(pdev->msix_enabled))
> >> +		return false;
> >> +
> >> +	if (pci_match_device_domain(pdev, DOMAIN_BUS_PCI_DEVICE_MSI))
> >> +		return true;
> >> +	if (pci_match_device_domain(pdev, DOMAIN_BUS_PCI_DEVICE_MSIX))
> >> +		msi_remove_device_irq_domain(&pdev->dev, MSI_DEFAULT_DOMAIN);
> >> +
> >> +	return pci_create_device_domain(pdev, &pci_msi_template, 1);
> >
> > Hardwired to one 1? What about multi-msi?
> 
> MSI has exactly ONE descriptor whether it's single or multi-MSI.
> 
> Multi-MSI can have several interrupts hanging off the same descriptor,
> but that's not how MSI looks at it because you write ONE message and the
> hardware does the substitution of the low bits depending on which vector
> is raised.

Okay, that is very clear, maybe this in a comment right here ?

Jason