linux-kernel - Re: [patch RFC 38/38] irqchip: Add IMS array driver

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Date:   Fri, 21 Aug 2020 09:45:47 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     LKML <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Marc Zyngier <maz@...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>,
        Joerg Roedel <joro@...tes.org>,
        <iommu@...ts.linux-foundation.org>, <linux-hyperv@...r.kernel.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "Jon Derrick" <jonathan.derrick@...el.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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [patch RFC 38/38] irqchip: Add IMS array driver - NOT FOR MERGING

On Fri, Aug 21, 2020 at 02:25:02AM +0200, Thomas Gleixner wrote:
> +static void ims_mask_irq(struct irq_data *data)
> +{
> +	struct msi_desc *desc = irq_data_get_msi_desc(data);
> +	struct ims_array_slot __iomem *slot = desc->device_msi.priv_iomem;
> +	u32 __iomem *ctrl = &slot->ctrl;
> +
> +	iowrite32(ioread32(ctrl) & ~IMS_VECTOR_CTRL_UNMASK, ctrl);

Just to be clear, this is exactly the sort of operation we can't do
with non-MSI interrupts. For a real PCI device to execute this it
would have to keep the data on die.

I saw the idxd driver was doing something like this, I assume it
avoids trouble because it is a fake PCI device integrated with the
CPU, not on a real PCI bus?

It is really nice to see irq_domain used properly in x86!

Thanks,
Jason