┌───────┐ ┌──────────┐
│ │ │ │
┌─────────────┐ │ │ │ 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
