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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Marc Zyngier <maz@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Dave Jiang <dave.jiang@intel.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Kevin Tian <kevin.tian@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Ashok Raj <ashok.raj@intel.com>, Jon Mason <jdmason@kudzu.us>,
        Allen Hubbe <allenbh@gmail.com>,
        "Ahmed S. Darwish" <darwi@linutronix.de>,
        Reinette Chatre <reinette.chatre@intel.com>
Subject: Re: [patch 12/33] PCI/MSI: Add support for per device MSI[X] domains
In-Reply-To: <Y3V+u+h7jGbRj3cE@nvidia.com>
References: <20221111133158.196269823@linutronix.de>
 <20221111135205.951710169@linutronix.de> <Y3U2QFeoDB17kbIC@nvidia.com>
 <87tu2yo77n.ffs@tglx> <Y3V+u+h7jGbRj3cE@nvidia.com>
Date:   Thu, 17 Nov 2022 09:45:53 +0100
Message-ID: <87wn7um0ji.ffs@tglx>
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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.