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SubjectRe: [patch V2 34/46] PCI/MSI: Make arch_.*_msi_irq[s] fallbacks selectable
[+cc Rob,

On Wed, Aug 26, 2020 at 01:17:02PM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <>
> The arch_.*_msi_irq[s] fallbacks are compiled in whether an architecture
> requires them or not. Architectures which are fully utilizing hierarchical
> irq domains should never call into that code.
> It's not only architectures which depend on that by implementing one or
> more of the weak functions, there is also a bunch of drivers which relies
> on the weak functions which invoke msi_controller::setup_irq[s] and
> msi_controller::teardown_irq.
> Make the architectures and drivers which rely on them select them in Kconfig
> and if not selected replace them by stub functions which emit a warning and
> fail the PCI/MSI interrupt allocation.

Sorry, I really don't understand this, so these are probably stupid

If CONFIG_PCI_MSI_ARCH_FALLBACKS is defined, we will supply
implementations of:

default_teardown_msi_irqs # non-weak

You select CONFIG_PCI_MSI_ARCH_FALLBACKS for ia64, mips, powerpc,
s390, sparc, and x86. I see that all of those arches implement at
least one of the functions above. But x86 doesn't and I can't figure
out why it needs to select CONFIG_PCI_MSI_ARCH_FALLBACKS.

I assume there's a way to convert these arches to hierarchical irq
domains so they wouldn't need this at all? Is there a sample
conversion to look at?

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

> --- a/include/linux/msi.h
> +++ b/include/linux/msi.h
> @@ -193,17 +193,38 @@ void pci_msi_mask_irq(struct irq_data *d
> void pci_msi_unmask_irq(struct irq_data *data);
> /*
> - * The arch hooks to setup up msi irqs. Those functions are
> - * implemented as weak symbols so that they /can/ be overriden by
> - * architecture specific code if needed.
> + * The arch hooks to setup up msi irqs. Default functions are implemented

s/msi/MSI/ to match the one below.

> + * as weak symbols so that they /can/ be overriden by architecture specific
> + * code if needed. These hooks must be enabled by the architecture or by
> + * drivers which depend on them via msi_controller based MSI handling.

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