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Problem with interrupt support for vhost-device-gpio and QEMU 8.1.1 #613
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With the above modification, the Linux kernel displays a complaint:
|
…e-gpio. Note that working with interrupts in QEMU requires small modification. It has been proposed in: rust-vmm#613
@wzab I never tested it with PCI but MMIO and it worked. Please send a fix to QEMU mailing list for this. Thanks. |
Yeah, the irq chip needs some minor changes. If you are okay, then please send a fix for that. I can review it for you. Something like this: f56914393537 gpio: zynq: fix zynqmp_gpio not an immutable chip warning |
I have created the related issue in QEMU repository: https://gitlab.com/qemu-project/qemu/-/issues/2167 |
I tried to test connecting simulated GPIO peripherals to QEMU using vhost-device-gpio.
I have successfully built the vhost-device-gpio (with
cargo build --features "mock_gpio"
) and tried to connect it to the Linux running on a qemu-aarch64-virt machine, built with Buildroot version 2023.11.1.Of course, I had to add
CONFIG_GPIO_VIRTIO=m
in the Linux kernel configuration.In the virtual machine, I have loaded the driver with
modprobe gpio-virtio
. Then, I could access the simulated GPIO controlling the direction and values.However, when I tried to test interrupt functionality with
gpiomon 0 0
, I got an error:After some investigations, I have found the cause. The feature VIRTIO_GPIO_F_IRQ was not set for the created virtio gpio device.
Further investigation required compiling QEMU with debugging symbols and running it under gdb.
With that, I could find that the problem is caused by the fact that this flag is not set in the
host_features
invirtio-pci.c
source in QEMU.As a quick workaround, I have modified the function virtio_pci_pre_plugged, adding the lacking feature here:
With such a modified QEMU, I was able to activate emulation of IRQs with vhost-device-gpio.
That is a QEMU problem, but it is highly specific to vhost-device-gpio. Therefore, I've described it here.
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