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Date: Fri, 28 Aug 2020 09:19:44 -0300
From: Jason Gunthorpe <jgg@nvidia.com>
Subject: Re: [patch V2 34/46] PCI/MSI: Make arch_.*_msi_irq[s] fallbacks
 selectable
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To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, LKML <linux-kernel@vger.kernel.org>, x86@kernel.org, Joerg Roedel <joro@8bytes.org>, iommu@lists.linux-foundation.org, linux-hyperv@vger.kernel.org, Haiyang Zhang <haiyangz@microsoft.com>, Jon Derrick <jonathan.derrick@intel.com>, Lu Baolu <baolu.lu@linux.intel.com>, Wei Liu <wei.liu@kernel.org>, "K. Y. Srinivasan" <kys@microsoft.com>, Stephen Hemminger <sthemmin@microsoft.com>, Steve Wahl <steve.wahl@hpe.com>, Dimitri Sivanich <sivanich@hpe.com>, Russ Anderson <rja@hpe.com>, linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, xen-devel@lists.xenproject.org, Juergen Gross <jgross@suse.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Stefano Stabellini <sstabellini@kernel.org>, Marc Zyngier <maz@kernel.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>, Megha Dey <megha.dey@intel.com>, Dave Jiang <dave.jiang@intel.com>, Alex Williamson <alex.williamson@redhat.com>, Jacob Pan <jacob.jun.pan@intel.com>, Baolu Lu <baolu.lu@intel.com>, Kevin Tian <kevin.tian@intel.com>, Dan Williams <dan.j.williams@intel.com>, Rob Herring <robh@kernel.org>

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