linux-kernel - Re: [patch RFC 30/38] PCI/MSI: Allow to disable arch fallbacks

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Message-ID: <20200825213501.GA1931388@bjorn-Precision-5520>
Date:   Tue, 25 Aug 2020 16:35:01 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        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>,
        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>,
        Jason Gunthorpe <jgg@...lanox.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 RFC 30/38] PCI/MSI: Allow to disable arch fallbacks

On Tue, Aug 25, 2020 at 11:28:30PM +0200, Thomas Gleixner wrote:
> On Tue, Aug 25 2020 at 15:07, Bjorn Helgaas wrote:
> >> + * The arch hooks to setup up msi irqs. Default functions are implemented
> >> + * as weak symbols so that they /can/ be overriden by architecture specific
> >> + * code if needed.
> >> + *
> >> + * They can be replaced by stubs with warnings via
> >> + * CONFIG_PCI_MSI_DISABLE_ARCH_FALLBACKS when the architecture fully
> >> + * utilizes direct irqdomain based setup.

> > If not, it seems like it'd be nicer to have the burden on the arches
> > that need/want to use arch-specific code instead of on the arches that
> > do things generically.
> 
> Right, but they still share the common code there and some of them
> provide only parts of the weak callbacks. I'm not sure whether it's a
> good idea to copy all of this into each affected architecture.
> 
> Or did you just mean that those architectures should select
> CONFIG_I_WANT_THE CRUFT instead of opting out on the fully irq domain
> based ones?

Yes, that was my real question -- can we confine the cruft in the
crufty arches?  If not, no big deal.

Bjorn