Re: [PATCH v1 5/5] docs: Describe virtio-msg-amp-pci

["Alex Bennée" <alex.bennee@linaro.org>]

"Edgar E. Iglesias" <edgar.iglesias@gmail.com> writes:

> From: "Edgar E. Iglesias" <edgar.iglesias@amd.com>
>
> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
> ---
>  .../devices/virtio/virtio-msg-amp-pci.rst     | 70
> +++++++++++++++++++

You also need to add this to index.rst otherwise the docs build will
fail.


>  1 file changed, 70 insertions(+)
>  create mode 100644 docs/system/devices/virtio/virtio-msg-amp-pci.rst
>
> diff --git a/docs/system/devices/virtio/virtio-msg-amp-pci.rst b/docs/system/devices/virtio/virtio-msg-amp-pci.rst
> new file mode 100644
> index 0000000000..c73f7a878b
> --- /dev/null
> +++ b/docs/system/devices/virtio/virtio-msg-amp-pci.rst
> @@ -0,0 +1,70 @@
> +Virtio-msg AMP PCI
> +==================
> +
> +This document explains the setup and usage of the virtio-msg-amp-pci device..
> +The virtio-msg-amp-pci, is an emulated PCI device that provides a small
> +set of features to enable virtio-msg over shared-memory queue's.
> +
> +Usecase
> +-------
> +
> +Virtio-msg is a virtio transport where driver and device communicate over
> +messages rather than using memory accesses that get trapped and emulated.
> +Virtio-msg depends on a lower lever virtio-msg-bus responsible for delivering
> +these messages. In this case, we're using the Virtio-msg AMP bus which moves
> +messages back and forth using a FIFO on top of shared-memory and interrupts.
> +
> +The virtio-msg-amp-pci device exposes a BAR with RAM and doorbell registers
> +so guests can implement the shared-memory FIFO protocol and QEMU implements
> +the backend side of it.
> +
> +Virtio pmem allows to bypass the guest page cache and directly use
> +host page cache. This reduces guest memory footprint as the host can
> +make efficient memory reclaim decisions under memory pressure.
> +
> +Virtio-msg-amp-pci PCI device
> +-----------------------------
> +
> +The virtio-msg-amp-pci device has the following layout:
> +
> +- BAR 0: Registers (Version, features and notification/doorbell regs)
> +- BAR 1: RAM for FIFOs
> +
> +Each FIFO gets an MSI-X interrupt reserved for it and a dedicated doorbell
> +register::
> +
> +        REG32(VERSION,  0x00)
> +        REG32(FEATURES, 0x04)
> +        REG32(NOTIFY0,  0x20)
> +        REG32(NOTIFY1,  0x24)
> +        REG32(NOTIFY2,  0x28)
> +        And so on.
> +
> +How does virtio-msg-amp-pci compare to virtio-pci emulation?
> +------------------------------------------------------------
> +
> +Both virtio-msg-amp-pci and virtio-pci emulate PCI devices and allow users
> +to plug virtio devices behind them. The main difference is in how the
> +guest uses virtio-msg vs virtio-pci to discover and configure the virtio dev.
> +
> +virtio pmem usage
> +-----------------
> +
> +A virtio-msg-amp-pci can be greated by adding the following to the QEMU
> +command-line::
> +
> +    -device virtio-msg-amp-pci
> +
> +Virtio devices can then be attached to the virtio-msg bus with for example
> +the following::
> +
> +    -device virtio-rng-device,bus=/gpex-pcihost/pcie.0/virtio-msg-amp-pci/fifo0/virtio-msg/bus0/virtio-msg-dev
> +
> +Multiple virtio devices can be connected by using bus1, bus2 and so on.
> +
> +Device properties
> +-----------------
> +
> +The virtio-msg-amp-pci  device can be configured with the following properties:
> +
> + * ``num-fifos`` number of fifos (default 2).

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro