Re: [RFC] Proposal of QEMU PCI Endpoint test environment

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Fri, Aug 18, 2023 at 10:46:02PM +0900, Shunsuke Mie wrote:
> Hi all,
> 
> We are proposing to add a new test syste to Linux for PCIe Endpoint. That
> can be run on QEMU without real hardware. At present, partially we have
> confirmed that pci-epf-test is working, but it is not yet complete.
> However, we would appreciate your comments on the architecture design.
> 
> # Background
> The background is as follows.
> 
> PCI Endpoint function driver is implemented using the PCIe Endpoint
> framework, but it requires physical boards for testing, and it is difficult
> to test sufficiently. In order to find bugs and hardware-dependent
> implementations early, continuous testing is required. Since it is
> difficult to automate tests that require hardware, this RFC proposes a
> virtual environment for testing PCI endpoint function drivers.
> 

This sounds exciting to me and yes, it is going to be really helpful for
validating EP framework as a whole.

> # Architecture
> The overview of the architecture is as follows.
> 
>   Guest 1                        Guest 2
> +-------------------------+    +----------------------------+
> | Linux kernel            |    | Linux kernel               |
> |                         |    |                            |
> | PCI EP function driver  |    |                            |
> | (e.g. pci-epf-test)     |    |                            |
> |-------------------------|    | PCI Device Driver          |
> | (2) QEMU EPC Driver     |    | (e.g. pci_endpoint_test)   |
> +-------------------------+    +----------------------------+
> +-------------------------+    +----------------------------+
> | QEMU                    |    | QEMU                       |
> |-------------------------|    |----------------------------|
> | (1) QEMU PCI EPC Device *----* (3) QEMU EPF Bridge Device |
> +-------------------------+    +----------------------------+
> 
> At present, it is designed to work guests only on the same host, and
> communication is done through Unix domain sockets.
> 
> The three parts shown in the figure were introduced this time.
> 
> (1) QEMU PCI Endpoint Controller(EPC) Device
> PCI Endpoint Controller implemented as QEMU PCI device.
> (2) QEMU PCI Endpoint Controller(EPC) Driver
> Linux kernel driver that drives the device (1). It registers a epc device
> to linux kernel and handling each operations for the epc device.
> (3) QEMU PCI Endpoint function(EPF) Bridge Device
> QEMU PCI device that cooperates with (1) and performs accesses to pci
> configuration space, BAR and memory space to communicate each guests, and
> generates interruptions to the guest 1.
> 

I'm not very familiar with Qemu, but why can't the existing Qemu PCIe host
controller devices used for EP communication? I mean, what is the need for a
dedicated EPF bridge device (3) in host? (Guest 2 as per your diagram).

Is that because you use socket communication between EP and host?

- Mani

> Each projects are:
> (1), (3) https://github.com/ShunsukeMie/qemu/tree/epf-bridge/v1
> files: hw/misc/{qemu-epc.{c,h}, epf-bridge.c}
> (2) https://github.com/ShunsukeMie/linux-virtio-rdma/tree/qemu-epc
> files: drivers/pci/controller/pcie-qemu-ep.c
> 
> # Protocol
> 
> PCI, PCIe has a layer structure that includes Physical, Data Lane and
> Transaction. The communicates between the bridge(3) and controller (1)
> mimic the Transaction. Specifically, a protocol is implemented for
> exchanging fd for communication protocol version check and communication,
> in addition to the interaction equivalent to PCIe Transaction Layer Packet
> (Read and Write of I/O, Memory, Configuration space and Message). In my
> mind, we need to discuss the communication mor.
> 
> We also are planning to post the patch set after the code is organized and
> the protocol discussion is matured.
> 
> Best regards,
> Shunsuke

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