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

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Message-ID: <87wn7um0ji.ffs@tglx>
Date:   Thu, 17 Nov 2022 09:45:53 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jason Gunthorpe <jgg@...dia.com>
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 20:22, Jason Gunthorpe wrote:
> 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 ?

Sure.