linux-kernel - Re: [patch V2 34/46] PCI/MSI: Make arch_.*_msi

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Date:   Fri, 28 Aug 2020 09:19:44 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:     Bjorn Helgaas <helgaas@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        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>,
        "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>,
        "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>,
        "Rob Herring" <robh@...nel.org>
Subject: Re: [patch V2 34/46] PCI/MSI: Make arch_.*_msi_irq[s] fallbacks
 selectable

On Fri, Aug 28, 2020 at 12:21:42PM +0100, Lorenzo Pieralisi wrote:
> On Thu, Aug 27, 2020 at 01:20:40PM -0500, Bjorn Helgaas wrote:
> 
> [...]
> 
> > And I can't figure out what's special about tegra, rcar, and xilinx
> > that makes them need it as well.  Is there something I could grep for
> > to identify them?  Is there a way to convert them so they don't need
> > it?
> 
> I think DT binding and related firmware support are needed to setup the
> MSI IRQ domains correctly, there is nothing special about tegra, rcar
> and xilinx AFAIK (well, all native host controllers MSI handling is
> *special* just to be polite but let's gloss over this for the time
> being).
> 
> struct msi_controller, to answer the first question.
> 
> I have doubts about pci_mvebu too, they do allocate an msi_controller
> but without methods so it looks pretty much useless.

Oh, I did once know things about mvebu.. 

I suspect the msi controller pointer assignment is dead code at this
point. The only implementation of MSI with that PCI root port is
drivers/irqchip/irq-armada-370-xp.c which looks like it uses
irq_domain.

Actually looks like things are very close to eliminating
msi_controller.

This is dead code, can't find a setter for hw_pci->msi_ctrl:

arch/arm/include/asm/mach/pci.h:        struct msi_controller *msi_ctrl;
arch/arm/kernel/bios32.c:                               bridge->msi = hw->msi_ctrl;

This is probably just copying NULL from one place to another:

drivers/pci/controller/pci-mvebu.c:     struct msi_controller *msi;

These need conversion to irq_domain (right?):

drivers/pci/controller/pci-hyperv.c:    struct msi_controller msi_chip;
drivers/pci/controller/pci-tegra.c:     struct msi_controller chip;
drivers/pci/controller/pcie-rcar-host.c:        struct msi_controller chip;
drivers/pci/controller/pcie-xilinx.c:static struct msi_controller xilinx_pcie_msi_chip = {

Then the stuff in drivers/pci/msi.c can go away.

So the arch_setup_msi_irq/etc is not really an arch hook, but some
infrastructure to support those 4 PCI root port drivers.

Jason