linux-kernel - RE: [patch V3 12/33] PCI/MSI: Add support for per device MSI[X] domains

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Date:   Mon, 28 Nov 2022 04:46:27 +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 V3 12/33] PCI/MSI: Add support for per device MSI[X]
 domains

> From: Thomas Gleixner <tglx@...utronix.de>
> Sent: Friday, November 25, 2022 7:26 AM
> +
> +	if (!irq_domain_is_msi_parent(domain)) {
> +		/*
> +		 * For "global" PCI/MSI interrupt domains the associated
> +		 * msi_domain_info::flags is the authoritive source of
> +		 * information.
> +		 */
> +		info = domain->host_data;
> +		supported = info->flags;
> +	} else {
> +		/*
> +		 * For MSI parent domains the supported feature set
> +		 * is avaliable in the parent ops. This makes checks
> +		 * possible before actually instantiating the
> +		 * per device domain because the parent is never
> +		 * expanding the PCI/MSI functionality.
> +		 */
> +		supported = domain->msi_parent_ops->supported_flags;
> +	}

As discussed in v2 it's probably clearer to also mark out that it's always
the direct parent putting restrictions on all existing architectures. That
is why checking direct parent is sufficient here.