[PATCH v9 0/4] PCI EP driver support MSI doorbell from host

Frank Li
2022-09-07T03:49:18Z

┌───────┐ ┌──────────┐
│ │ │ │
┌─────────────┐ │ │ │ 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 v8 to v9
fix dt_bind_check error

- Change from v7 to v8
irqchip: using name process-a-side as resource bind name
pcie: endpoint:
- fix build error reported by kernel test robot <lkp@intel.com>
- rename epf_db_phy to epf_db_phys
- rework error message
- rework commit message
- change ntb to vtb at apply irq.
- kept name msi_virqbase because it is msi irq base number,
not base address.

- Change from v6 to v7
pcie: endpoint: add endpoint MSI support
Fine tuning commit message
Fixed issues, reviewed by Bjorn Helgaas

- Change from v5 to v6
Fixed build error found by kernel test robot

- Change from v4 to v5
Fixed dt-binding document
add msi-cell
add interrupt max number
update naming reg-names and power-domain-names.
Fixed irqchip-Add-IMX-MU-MSI-controller-driver.patch
rework commit message
remove some field in struct imx_mu_dcfg
error handle when link power domain failure.
add irq_domain_update_bus_token

- Change from v3 to v4
Fixed dt-binding document according to Krzysztof Kozlowski's feedback
Fixed irqchip-imx-mu-worked-as-msi-controller according to Marc Zyngier's
comments.

There are still two important points, which I am not sure.
1. clean irq_set_affinity after platform_msi_create_irq_domain.
Some function, like platform_msi_write_msg() is static.
so I have to set MSI_FLAG_USE_DEF_CHIP_OPS flags, which will
set irq_set_affinity to default one.
2. about comments

> + msi_data->msi_domain = platform_msi_create_irq_domain(
> + of_node_to_fwnode(msi_data->pdev->dev.of_node),
> + &imx_mu_msi_domain_info,
> + msi_data->parent);

"And you don't get an error due to the fact that you use the same
fwnode for both domains without overriding the domain bus token?"

I did not understand yet.

Fixed static check warning, reported by Dan Carpenter
pcie: endpoint: pci-epf-vntb: add endpoint MSI support

- 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

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2.35.1