Hi, On 3/30/21 10:11 AM, Marc Zyngier wrote:
We have now three ways of ending up with NO_MSI being set. Document them. Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> --- drivers/pci/msi.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c index d9c73c173c14..217dc9f0231f 100644 --- a/drivers/pci/msi.c +++ b/drivers/pci/msi.c @@ -871,8 +871,15 @@ static int pci_msi_supported(struct pci_dev *dev, int nvec) * Any bridge which does NOT route MSI transactions from its * secondary bus to its primary bus must set NO_MSI flag on * the secondary pci_bus. - * We expect only arch-specific PCI host bus controller driver - * or quirks for specific PCI bridges to be setting NO_MSI. + * + * The NO_MSI flag can either be set directly by: + * - arch-specific PCI host bus controller drivers (deprecated) + * - quirks for specific PCI bridges + * + * or indirectly by platform-specific PCI host bridge drivers by + * advertising the 'msi_domain' property, which results in + * the NO_MSI flag when no MSI domain is found for this bridge + * at probe time.
I have an ACPI machine with a gicv2 (no m), and a MSI region that isn't described by ACPI because its non-standard. In the past this tended to work because PCIe device drivers would fall back to legacy pci intx silently. But, with 5.13, it seems this series now triggers the WARN_ON_ONCE() in arch_setup_msi_irq, because duh, no MSI support.
Everything of course continues to work, it just gets this ugly splat on bootup telling me basically the machine doesn't support MSIs. So, I considered a few patches, including just basically setting nomsi if gicv2 && acpi, or eek a host bridge quirk.
None of these seem great, so how can this be fixed? Thanks,
*/ for (bus = dev->bus; bus; bus = bus->parent) if (bus->bus_flags & PCI_BUS_FLAGS_NO_MSI)
