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

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Date:   Sun, 23 Aug 2020 10:03:07 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jason Gunthorpe <jgg@...dia.com>
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 Sat, Aug 22 2020 at 20:05, Jason Gunthorpe wrote:
> On Sat, Aug 22, 2020 at 03:34:45AM +0200, Thomas Gleixner wrote:
> As a silicon design it might work, but it means existing devices can't
> be used with this dev_msi. It is also the sort of thing that would
> need a standard document to have any hope of multiple vendors fitting
> into it. Eg at PCI-SIG or something.

Fair enough.

>> If you don't do that then you simply can't write to that space from the
>> CPU and you have to transport this kind information always via command
>> queues.
>
> Yes, exactly. This is part of the architectural design of the device,
> has been for a long time. Has positives and negatives.

As always and it clearly follows the general HW design rule "we can fix
that in software".

>> > I suppose the core code could provide this as a service? Sort of a
>> > varient of the other lazy things above?
>> 
>> Kinda. That needs a lot of thought for the affinity setting stuff
>> because it can be called from contexts which do not allow that. It's
>> solvable though, but I clearly need to stare at the corner cases for a
>> while.
>
> If possible, this would be ideal, as we could use the dev_msi on a big
> installed base of existing HW.

I'll have a look, but I'm surely not going to like the outcome.

Thanks,

        tglx