linux-kernel - Re: [patch V2 24/46] PCI: vmd: Mark VMD irqdomain with DOMAIN_BUS_VMD

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Message-ID: <20200831143940.GA1152540@nvidia.com>
Date:   Mon, 31 Aug 2020 11:39:40 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Jon Derrick <jonathan.derrick@...el.com>
CC:     LKML <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        <iommu@...ts.linux-foundation.org>, <linux-hyperv@...r.kernel.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "Lu Baolu" <baolu.lu@...ux.intel.com>,
        Wei Liu <wei.liu@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steve Wahl <steve.wahl@....com>,
        Dimitri Sivanich <sivanich@....com>,
        "Russ Anderson" <rja@....com>, <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
        <xen-devel@...ts.xenproject.org>, Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Megha Dey" <megha.dey@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Alex Williamson" <alex.williamson@...hat.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Baolu Lu <baolu.lu@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [patch V2 24/46] PCI: vmd: Mark VMD irqdomain with
 DOMAIN_BUS_VMD_MSI

On Wed, Aug 26, 2020 at 01:16:52PM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Devices on the VMD bus use their own MSI irq domain, but it is not
> distinguishable from regular PCI/MSI irq domains. This is required
> to exclude VMD devices from getting the irq domain pointer set by
> interrupt remapping.
> 
> Override the default bus token.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
>  drivers/pci/controller/vmd.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> +++ b/drivers/pci/controller/vmd.c
> @@ -579,6 +579,12 @@ static int vmd_enable_domain(struct vmd_
>  		return -ENODEV;
>  	}
>  
> +	/*
> +	 * Override the irq domain bus token so the domain can be distinguished
> +	 * from a regular PCI/MSI domain.
> +	 */
> +	irq_domain_update_bus_token(vmd->irq_domain, DOMAIN_BUS_VMD_MSI);
> +

Having the non-transparent-bridge hold a MSI table and
multiplex/de-multiplex IRQs looks like another good use case for
something close to pci_subdevice_msi_create_irq_domain()?

If each device could have its own internal MSI-X table programmed
properly things would work alot better. Disable capture/remap of the
MSI range in the NTB.

Then each device could have a proper non-multiplexed interrupt
delivered to the CPU.. Affinity would work properly, no need to share
IRQs (eg vmd_irq() goes away)/etc.

Something for the VMD maintainers to think about at least.

As I hear more about NTB these days a full MSI scheme for NTB seems
interesting to have in the PCI-E core code..

Jason