Hi Lukas, On Tue, Feb 04, 2025 at 10:23:45AM +0100, Lukas Wunner wrote: > On Tue, Feb 04, 2025 at 01:37:58PM +0800, Feng Tang wrote: > > There was a irq storm bug when testing "pci=nomsi" case, and the root > > cause is: 'nomsi' will disable MSI and let devices and root ports use > > legacy INTX inerrupt, and likely make several devices/ports share one > > interrupt. In the failure case, BIOS doesn't disable the PCIE hotplug > > interrupts, and actually asserts the command-complete interrupt. > > As MSI is disabled, ACPI initialization code will not enumerate root > > port's PCIE hotplug capability, and pciehp service driver wont' be > > enabled for the root port to handle that interrupt, later on when it is > > shared and enabled by other device driver like NVME or NIC, the "nobody > > care irq storm" happens. > > Is there a section in the PCI Firmware Spec which says ACPI doesn't > enumerate the hotplug capability if MSI is disabled? No, I didn't get it from spec, but found the logic by code reading during debugging the irq storm issue. The related code is about: #define ACPI_PCIE_REQ_SUPPORT (OSC_PCI_EXT_CONFIG_SUPPORT \ | OSC_PCI_ASPM_SUPPORT \ | OSC_PCI_CLOCK_PM_SUPPORT \ | OSC_PCI_MSI_SUPPORT) acpi_pci_root_add negotiate_os_control calculate_support if (pci_msi_enabled()) support |= OSC_PCI_MSI_SUPPORT; decode_osc_support os_control_query_checks if ((support & ACPI_PCIE_REQ_SUPPORT) != ACPI_PCIE_REQ_SUPPORT) return false acpi_pci_osc_control_set And later in get_port_device_capability(), the pciehp service bit won't be set, and driver is not loaded. Thanks, Feng > If so, it should be referenced in the commit message. > > If not, I'm wondering if it's safe to fiddle with the Slot Control > register given the platform hasn't granted OSPM control of it. > > Of course if this is spec-defined behavior in the nomsi case, > we could make the write to the Slot Control register conditional > on that. But if this turns out to be platform-specific behavior, > we can't deal with it in generic PCI code but only in a quirk. > > Thanks, > > Lukas
