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

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Date:   Tue, 26 Sep 2023 18:47:50 +0900
From:   Shunsuke Mie <mie@...l.co.jp>
To:     Kishon Vijay Abraham I <kvijayab@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>, vaishnav.a@...com
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Marcel Apfelbaum <marcel.apfelbaum@...il.com>,
        qemu-devel@...gnu.org, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org,
        Krzysztof Wilczyński <kw@...ux.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>
Subject: Re: [RFC] Proposal of QEMU PCI Endpoint test environment


On 2023/09/21 18:11, Kishon Vijay Abraham I wrote:
> +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.

I got it. I'll make a table to compare some methods that includes 
greybus to realize this emulation environment.


Best,

Shunsuke

> 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