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

[Kishon Vijay Abraham I]

+Vaishnav

Hi Shunsuke,

On 8/18/2023 7:16 PM, 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 would be quite useful and thank you for attempting it! I would like 
to compare other mechanisms available in-addition to QEMU before going 
with the QEMU approach.

Though I don't understand this fully, Looking at 
https://osseu2023.sched.com/event/1OGk8/emulating-devices-in-linux-using-greybus-subsystem-vaishnav-mohandas-achath-texas-instruments, 
Vaishnav seems to solve the same problem using greybus for multiple type 
s of devices.

Vaishnav, we'd wait for your OSS presentation but do you have any 
initial thoughts on how greybus could be used to test PCIe endpoint drivers?

Thanks,
Kishon

> # 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.
>
> Each projects are:
> (1), (3) https://github.com/ShunsukeMie/qemu/tree/epf-bridge/v1 
> <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 
> <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