R-Car/Virtualization/VFIO

Device Pass-Through Using VFIO

Platform Device Pass-Through Prototype

This is a proof-of-concept showing how to provide guest access to an R-Car GPIO controller block on the Renesas Salvator-X and Salvator-XS boards.

Host Side

• Build and boot a host kernel using:
  • Repository: https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git
  • Branch: "topic/rcar3-virt-gpio-passthrough-v2"
  • Config: "renesas_defconfig"

• Configure workarounds for missing functionality:

$ echo 1 > /sys/module/vfio/parameters/enable_unsafe_noiommu_mode

• Unbind GPIO6 from the "gpio-rcar" driver:

$ echo e6055400.gpio > /sys/bus/platform/drivers/gpio_rcar/unbind
gpio gpiochip6: REMOVING GPIOCHIP WITH GPIOS STILL REQUESTED

• Bind GPIO6 to the "vfio-platform" driver, for pass-through to guests:

$ echo vfio-platform > /sys/bus/platform/devices/e6055400.gpio/driver_override
$ echo e6055400.gpio > /sys/bus/platform/drivers/vfio-platform/bind
iommu: Adding device e6055400.gpio to group 0
vfio-platform e6055400.gpio: Adding kernel taint for vfio-noiommu group on device

Guest Side

• Build a guest kernel using:
  • Repository: https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git
  • Branch: "topic/rcar3-virt-gpio-passthrough-v2"
  • Config: "virt_defconfig"

• Build QEMU using:
  • Repository: https://github.com/geertu/qemu.git
  • Branch: "topic/rcar3-virt-gpio-passthrough-v2"

• When starting QEMU, specify pass-through of the GPIO6 platform device. The device specifier consists of three parts:

  $1a

  the device's node name, or

  $1b

  the full path to the device's node in sysfs,

  $2

  the manufacturer part of the device's compatible value,

  $3

  the model part of the device's compatible value.

I.e.:

-device vfio-platform,host=$1a,manufacturer=$2,model=$3
-device vfio-platform,host=e6055400.gpio,manufacturer=renesas,model=rcar-gen3-gpio
-device vfio-platform,sysfsdev=$1b,manufacturer=$2,model=$3
-device vfio-platform,sysfsdev=/sys/bus/platform/devices/e6055400.gpio,manufacturer=renesas,model=rcar-gen3-gpio

Full command line:

$ qemu-system-aarch64 -enable-kvm -M virt -cpu cortex-a57 -m 1024 -nographic \
        -kernel /path/to/guest/kernel/Image \
        -device vfio-platform,host=e6055400.gpio,manufacturer=renesas,model=rcar-gen3-gpio

Guest kernel output:

Booting Linux on physical CPU 0x0000000000 [0x411fd073]
Linux version 4.16.0-arm64-virt-00010-g8f416425ed2e81bb ...
...
gpio_rcar c000000.e6055400.gpio: driving 32 GPIOs
...

Host kernel output:

vfio-platform e6055400.gpio: reset
vfio-platform e6055400.gpio: vfio-noiommu device opened by user (qemu-system-aar:3003)

• Analysis of "/sys/firmware/devicetree/base" using "dtx_diff" shows that "e6055400.gpio@0" has been added as a subnode to the existing "platform@c000000" node:

--- /sys/firmware/devicetree/base.orig
+++ /sys/firmware/devicetree/base
@@ -124,6 +124,14 @@
                compatible = "qemu,platform", "simple-bus";
                interrupt-parent = <0x8001>;
                ranges = <0x0 0x0 0xc000000 0x2000000>;
+
+               e6055400.gpio@0 {
+                       #gpio-cells = <0x2>;
+                       compatible = "renesas,rcar-gen3-gpio";
+                       gpio-controller;
+                       interrupts = <0x0 0x70 0x4>;
+                       reg = <0x0 0x50>;
+               };
        };

        pmu {

• Export GPIOs used for LEDs (LED4/5/6), and turn all LEDs off:

# base=$(cat /sys/class/gpio/gpiochip*/base)
# for i in 11 12 13; do
    echo $(($base + $i)) > /sys/class/gpio/export
    echo low > /sys/class/gpio/gpio$(($base + $i))/direction
done

• Cycle through all LEDs, letting them blink once:

# for i in 11 12 13; do
    echo high > /sys/class/gpio/gpio$(($base + $i))/direction
    sleep 1
    echo low > /sys/class/gpio/gpio$(($base + $i))/direction
done

• Change the first GPIO from output to input, and configure edge detection to enable its interrupt:

# echo in > /sys/class/gpio/gpio$(($base + 11))/direction
# echo both > /sys/class/gpio/gpio$(($base + 11))/edge
# grep gpio /proc/interrupts
  5:          0     GIC-0 144 Level     c000000.e6055400.gpio
 42:          0  c000000.e6055400.gpio  11 Edge      gpiolib

• Monitor the GPIO interrupt (press button SW20 to trigger):

# while /bin/true; do grep gpiolib /proc/interrupts; done | uniq -c
      71298  42:          0  c000000.e6055400.gpio  11 Edge      gpiolib
        388  42:          1  c000000.e6055400.gpio  11 Edge      gpiolib
        247  42:          2  c000000.e6055400.gpio  11 Edge      gpiolib
        139  42:          3  c000000.e6055400.gpio  11 Edge      gpiolib
        586  42:          4  c000000.e6055400.gpio  11 Edge      gpiolib
^C

• Shut the guest down:

# poweroff

Guest kernel output:

reboot: Power down

Host kernel output:

vfio-platform e6055400.gpio: reset

The GPIO module has been reset, turning on all three LEDs.

Future Work

• IOMMU groups