mirror of https://github.com/torvalds/linux.git
8719c64e76
dw_pcie_ep_raise_msi_irq() currently programs an outbound iATU window for the MSI target address on every interrupt and tears it down again via dw_pcie_ep_unmap_addr(). On systems that heavily use the AXI bridge interface (for example when the integrated eDMA engine is active), this means the outbound iATU registers are updated while traffic is in flight. The DesignWare endpoint databook 5.40a - "3.10.6.1 iATU Outbound Programming Overview" warns that updating iATU registers in this situation is not supported, and the behavior is undefined. Under high MSI and eDMA load this pattern results in occasional bogus outbound transactions and IOMMU faults, on the RC side, such as: ipmmu-vmsa eed40000.iommu: Unhandled fault: status 0x00001502 iova 0xfe000000 followed by the system becoming unresponsive. This is the actual output observed on Renesas R-Car S4, with its ipmmu_hc used with PCIe ch0. There is no need to reprogram the iATU region used for MSI on every interrupt. The host-provided MSI address is stable while MSI is enabled, and the endpoint driver already dedicates a scratch buffer for MSI generation. Cache the aligned MSI address and map size, program the outbound iATU once, and keep the window enabled. Subsequent interrupts only perform a write to the MSI scratch buffer, avoiding dynamic iATU reprogramming in the hot path and fixing the lockups seen under load. dw_pcie_ep_raise_msix_irq() is not modified, as each vector can have a different msg_addr, and because the msg_addr is allowed to be changed while the vector is masked. Neither problem is easy to solve with the current design. Instead, the plan is for the DWC vendor drivers to transition to dw_pcie_ep_raise_msix_irq_doorbell(), which does not rely on the iATU. Signed-off-by: Koichiro Den <den@valinux.co.jp> [cassel: improve commit message] Signed-off-by: Niklas Cassel <cassel@kernel.org> Signed-off-by: Manivannan Sadhasivam <mani@kernel.org> Link: https://patch.msgid.link/20251222110144.3299523-2-cassel@kernel.org |
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