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

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Date:   Fri, 28 Aug 2020 13:47:59 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        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>,
        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

Hi Jason,

On 2020-08-28 13:19, Jason Gunthorpe wrote:
> 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.

I happen to have a *really old* patch addressing Tegra [1], which
I was never able to test (no HW). Rebasing it shouldn't be too hard,
and maybe you can find someone internally willing to give it a spin?

That'd be a good start towards the removal of this cruft.

Thanks,

         M.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/commit/?h=irq/kill-msi-controller&id=83b3602fcee7972b9d549ed729b56ec28de16081
-- 
Jazz is not dead. It just smells funny...