Re: [patch V2 34/46] PCI/MSI: Make arch_.*_msi_irq[s] fallbacks selectable

[Jason Gunthorpe <jgg@nvidia.com>]

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