┌───────┐ ┌──────────┐ │ │ │ │ ┌─────────────┐ │ │ │ PCI Host │ │ MSI │◄┐ │ │ │ │ │ Controller │ │ │ │ │ │ └─────────────┘ └─┼───────┼──────────┼─Bar0 │ │ PCI │ │ Bar1 │ │ Func │ │ Bar2 │ │ │ │ Bar3 │ │ │ │ Bar4 │ │ ├─────────►│ │ └───────┘ └──────────┘ Many PCI controllers provided Endpoint functions. Generally PCI endpoint is hardware, which is not running a rich OS, like linux. But Linux also supports endpoint functions. PCI Host write BAR<n> space like write to memory. The EP side can't know memory changed by the Host driver. PCI Spec has not defined a standard method to do that. Only define MSI(x) to let EP notified RC status change. The basic idea is to trigger an IRQ when PCI RC writes to a memory address. That's what MSI controller provided. EP drivers just need to request a platform MSI interrupt, struct MSI_msg *msg will pass down a memory address and data. EP driver will map such memory address to one of PCI BAR<n>. Host just writes such an address to trigger EP side IRQ. If system have gic-its, only need update PCI EP side driver. But i.MX have not chip support gic-its yet. So we have to use MU to simulate a MSI controller. Although only 4 MSI IRQs are simulated, it matched vntb(pci-epf-vntb) network requirement. After enable MSI, ping delay reduce < 1ms from ~8ms IRQchip: imx mu worked as MSI controller: let imx mu worked as MSI controllers. Although IP is not design as MSI controller, we still can use it if limited IRQ number to 4. pcie: endpoint: pci-epf-vntb: add endpoint MSI support Based on ntb-next branch. https://github.com/jonmason/ntb/commits/ntb-next Using MSI as door bell registers This patch is totally independent on previous on. It can be applied to ntb-next seperately. i.MX EP function driver is upstreaming by Richard Zhu. Some dts change missed at this patches. below is reference dts change --- a/arch/arm64/boot/dts/freescale/imx8-ss-hsio.dtsi +++ b/arch/arm64/boot/dts/freescale/imx8-ss-hsio.dtsi @@ -160,5 +160,6 @@ pcieb_ep: pcie_ep@5f010000 { num-ib-windows = <6>; num-ob-windows = <6>; status = "disabled"; + MSI-parent = <&lsio_mu12>; }; --- a/arch/arm64/boot/dts/freescale/imx8-ss-lsio.dtsi +++ b/arch/arm64/boot/dts/freescale/imx8-ss-lsio.dtsi @@ -172,6 +172,19 @@ lsio_mu6: mailbox@5d210000 { status = "disabled"; }; + lsio_mu12: mailbox@5d270000 { + compatible = "fsl,imx6sx-mu-MSI"; + msi-controller; + interrupt-controller; + reg = <0x5d270000 0x10000>, /* A side */ + <0x5d300000 0x10000>; /* B side */ + reg-names = "a", "b"; + interrupts = <GIC_SPI 191 IRQ_TYPE_LEVEL_HIGH>; + power-domains = <&pd IMX_SC_R_MU_12A>, + <&pd IMX_SC_R_MU_12B>; + power-domain-names = "a", "b"; + }; + Change Log - Change from v2 to v3 Fixed dt-binding docment check failure Fixed typo a cover letter. Change according Bjorn's comments at patch pcie: endpoint: pci-epf-vntb: add endpoint MSI support - from V1 to V2 Fixed fsl,mu-msi.yaml's problem Fixed irq-imx-mu-msi.c problem according Marc Zyngier's feeback Added a new patch to allow pass down .pm by IRQCHIP_PLATFORM_DRIVER_END -- 2.35.1