Re: [PATCH v15 04/15] irqchip/gic-v3-its: Add support for device tree msi-map and msi-mask

On Sat, Mar 01, 2025 at 11:37:14AM +0000, Marc Zyngier wrote:

On Tue, 11 Feb 2025 19:21:57 +0000, Frank Li Frank.Li@nxp.com wrote:

...

Some platform devices create child devices dynamically and require the parent device's msi-map to map device IDs to actual sideband information.

A typical use case is using ITS as a PCIe Endpoint Controller(EPC)'s doorbell function, where PCI hosts send TLP memory writes to the EP controller. The EP controller converts these writes to AXI transactions and appends platform-specific sideband information. See below figure.

           ┌────────────────────────────────┐
           │                                │
           │     PCI Endpoint Controller    │
           │                                │
           │  ┌─────┐   ┌─────┐     ┌─────┐ │
PCI Bus    │  │     │   │     │     │     │ │
─────────► │  │Func1│   │Func2│ ... │Func │ │
TLP Memory │  │     │   │     │     │<n>  │ │
Write Push │  │     │   │     │     │     │ │
DoorBell   │  └─┬─┬─┘   └──┬──┘     └──┬──┘ │
           │    │ │        │           │    │
           └────┼─┼────────┼───────────┼────┘
    sideband    │ │ Address│           │
    information ▼ ▼ /Data  ▼           ▼
               ┌────────────────────────┐
               │    MSI Controller      │
               └────────────────────────┘

Please stop using these figures in commit messages. I don't think they help, and they are not in consistent with the way the commit messages are managed.

Okay

...

EPC's DTS will provide such information by msi-map and msi-mask. A simplified dts as

pcie-ep@10000000 { ... msi-map = <0 &its 0xc 8>; ^^^ 0xc is implement defined sideband information, which append to AXI write transaction. ^ 0 is function index.

What does this sideband field represent?

ARM ITS use term "streamid" for this sideband field, which indicate which MSI consumer write to address/data pair on bus. Such as PCI1 or PCI2.

How is the ITS driver supposed to use that data?

ITS use a as devid, or info->scratchpad[0].ul = dev_id; msi-map actually given a start dev_id (it is 0xc in example) for fuction0. function1 will use dev_id + 1 ...

Is it the full devid as presented to the ITS?

Yes,

Something combined with the "function index"? Is the "function index" a full RID, as defined in the documentation?

Not a full RID. RID is related with host PCIe's topology. The EP function's RID may 1:00:01 at PC1, 3:00:01 at the another PC.

So Endpoint driver can't use RID directly. It should related function and virtual function number only.

PCI define 8 physicla funciton, and 64000 virutal function. Define device id as vfunc[31:3], pfunc[2:0] as msi-map's input. DTS provide information how map it to real streamid.

Also, msi-map is so far reserved to a PCIe RC, not this sort of wonky contraption. This needs to be documented.

Okay, I can update document.

Frank

...

msi-mask = <0x7> }

Check msi-map if msi-parent missed to keep compatility with existed system.

Signed-off-by: Frank Li Frank.Li@nxp.com

change from v14 to v15

• none

change from v13 to v14 new patch

---

drivers/irqchip/irq-gic-v3-its-msi-parent.c | 8 ++++++++ 1 file changed, 8 insertions(+)

diff --git a/drivers/irqchip/irq-gic-v3-its-msi-parent.c b/drivers/irqchip/irq-gic-v3-its-msi-parent.c index e150365fbe892..6c7389bb84a4a 100644 --- a/drivers/irqchip/irq-gic-v3-its-msi-parent.c +++ b/drivers/irqchip/irq-gic-v3-its-msi-parent.c @@ -118,6 +118,14 @@ static int of_pmsi_get_dev_id(struct irq_domain *domain, struct device *dev, index++; } while (!ret);

• if (ret) {

• struct device_node *np = NULL;
  

• ret = of_map_id(dev->of_node, dev->id, "msi-map", "msi-map-mask", &np, dev_id);
  

• if (np)
  

• 	of_node_put(np);
  

• }
• return ret;

}

Thanks,

M.

-- Without deviation from the norm, progress is not possible.