On Mon, 14 Jun 2021 at 15:00, Arnd Bergmann arnd@kernel.org wrote:
On Mon, Jun 14, 2021 at 2:50 PM Vincent Guittot via Stratos-dev stratos-dev@op-lists.linaro.org wrote:>
On Mon, 14 Jun 2021 at 14:33, Arnd Bergmann arnd@kernel.org wrote:
On Mon, Jun 14, 2021 at 12:23 PM Viresh Kumar viresh.kumar@linaro.org wrote:
I think most importantly we need a DT binding to describe what device nodes are supposed to look like underneath a virtio-mmio or virtio-pci device in order for a hypervisor to pass down the information to a guest OS in a generic way. We can probably borrow the USB naming, and replace compatible="usbVID,PID" with compatible="virtioDID", with the device ID in hexadecimal digits, such as "virtio22" for I2C (virtio device ID 34 == 0x22) if we decide to have a sub-node under the device, or we just point dev->of_node of the virtio device to the platform/pci device that is its parent in Linux.
Adding the Linux guest code to the virtio layer should be fairly straightforward, and I suppose it could be mostly copied from the corresponding code that added this for mmc in commit 25185f3f31c9 ("mmc: Add SDIO function devicetree subnode parsing") and for USB in commit 69bec7259853 ("USB: core: let USB device know device node") and 1a7e3948cb9f ("USB: add device-tree support for interfaces").
And something similar is also done with SCMI protocols which are defined in a SCMI node. A typical example:
cpu@0 { ... clocks = <&scmi_dvfs 0>; ... }; deviceX: deviceX@YYYYYYY { ... clocks = <&scmi_clk 0>; ... }; scmi: scmi { compatible = "arm,scmi-virtio"; #address-cells = <1>; #size-cells = <0>; scmi_devpd: protocol@11 { reg = <0x11>; #power-domain-cells = <1>; }; scmi_clk: protocol@14 { reg = <0x14>; #clock-cells = <1>; }; scmi_sensors: protocol@15 { reg = <0x15>; #thermal-sensor-cells = <1>; }; scmi_dvfs: protocol@13 { reg = <0x13>; #clock-cells = <1>; }; };But this example seem to be completely different from the ones I mentioned: The scmi node that you have here looks like it shows up under the root of the device tree, not below the virtio device that implements the scmi transport.
I was thinking of something like below:
deviceX: deviceX@YYYYYYY { ... gpio = <&virtio_gpio 0>; ... };
virtio_mmio@a000000 { dma-coherent; interrupts = <0x0 0x10 0x1>; reg = <0x0 0xa000000 0x0 0x200>; compatible = "virtio,mmio";
virtio_gpio: protocol@22 { reg = <0x22>; }; };
Arnd