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[Xen-devel] [PATCH 00/12 v3] PL011 emulation support in Xen

PL011 emulation for guests in Xen
Linaro has published VM System specification for ARM Processors, which
provides a set of guidelines for both guest OS and hypervisor implementations, 
such that building OS images according to these guidelines guarantees
that those images can also run on hypervisors compliant with this specification.

One of the spec requirements is that the hypervisor must provide an
emulated PL011 UART as a serial console which meets the minimum requirements in 
SBSA UART as defined in appendix B of the following ARM Server Base 
Architecture Document:


This feature allows the Xen guests to use SBSA compliant pl011 UART as 
as a console. 

Note that SBSA pl011 UART is a subset of full featured ARM pl011 UART and
supports only a subset of registers as mentioned below. It does not support
rx/tx DMA.

Currently, Xen supports paravirtualized (aka PV console) and an emulated serial 
consoles. This feature will expose an emulated SBSA pl011 UART console to the
guest, which a user can access using xenconsole.

The device tree passed to the guest VM will contain the pl011 MMIO address 
range and an irq for receiving rx/tx pl011 interrupts. The device tree format 
is specified in Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt.

The Xen hypervisor will expose two types of interfaces to the backend and domU. 

The interface exposed to domU will be an emulated pl011 UART by emulating the 
access to the following pl011 registers by the guest.

- Data register (DR)            - RW
- Raw interrupt status register (RIS)   - RO
- Masked interrupt status register (MIS)- RO
- Interrupt Mask (IMSC)         - RW
- Interrupt Clear (ICR)         - WO

It will also inject the pl011 interrupts to the guest in the following 

- incoming data in the rx buffer for the guest
- there is space in the tx buffer for the guest to write more data

The interface exposed to the backend will be the same PV console interface, 
which minimizes the changes required in xenconsole to support a new pl011 

This interface has rx and tx ring buffers and an event channel for 
sending/receiving events from the backend. 

So essentially Xen handles the data on behalf of domU and the backend. Any data 
written by domU is captured by Xen and written to the TX (OUT) ring buffer 
and a pl011 event is raised to the backend to read the TX ring buffer.
Similarly on reciving a pl011 event, Xen injects an interrupt to guest to
indicate there is data available in the RX (IN) ring buffer.

The pl011 UART state is completely captured in the set of registers 
mentioned above and this state is updated everytime there is an event from 
the backend or there is register read/write access from domU. 

For example, if domU has masked the rx interrupt in the IMSC register, then Xen 
will not inject an interrupt to guest and will just update the RIS register. 
Once the interrupt is unmasked by guest, the interrupt will be delivered to the 

Changes summary:

Xen Hypervisor

1. Add emulation code to emulate read/write access to pl011 registers and pl011 
    - It emulates DR read/write by reading and writing from/to the IN and 
      OUT ring buffers and raising an event to dom0 when there is data in 
      the OUT ring buffer and injecting an interrupt to the guest when there 
      is data in the IN ring buffer.
    - Other registers are related to interrupt management and essentially 
      control when interrupts are delivered to the guest.

2. Add two new domctl APIs to initialize and de-initialize vpl011 emulation in 

3. Enable vpl011 emulation for a domain based on a libxl option passed during 
   domain creation.


1. Add a new option "vuart" in the domU configuration file to enable/disable 

2. Create a SBSA UART DT node in the guest device tree. It uses a fixed
   vpl011 SPI IRQ number and MMIO address.

3. Call vpl011 init DOMCTL API to enable vpl011 emulation.

4. Call vpl011 de-init DOMCTL API to disable vpl011 emulation.

5. Add a new vuart xenstore node, which contains:
    - ring-ref
    - event channel
    - buffer limit
    - type


1. Split the domain structure to support multiple consoles.

2. Modify different APIs such as buffer_append() etc. to operate on the 
   console structure.
3. Add a new generic console_create_ring() function which maps the console GFN 
   and binds the event channel for a given console.

4. Modify domain_create_ring() to use console_create_ring() for a new console.

5. Modifications in handle_ring_read() to handle both PV and VUART

The vpl011 changes available at the following repo:

url: ssh://git@xxxxxxxxxxxxxx:/people/bhupinder.thakur/xen.git
branch: vpl011_v3

Bhupinder Thakur (12):
  xen/arm: vpl011: Move vgic register access functions to vreg.h
  xen/arm: vpl011: Define generic vreg_reg* access functions in vreg.h
  xen/arm: vpl011: Add pl011 uart emulation in Xen
  xen/arm: vpl011: Add support for vuart in libxl
  xen/arm: vpl011: Add new domctl APIs to initialize/de-initialize
  xen/arm: vpl011: Add a new vuart node in the xenstore
  xen/arm: vpl011: Allocate a new GFN in the toolstack for vuart
  xen/arm: vpl011: Modify xenconsole to support multiple consoles
  xen/arm: vpl011: Add support for vuart in xenconsole
  xen/arm: vpl011: Add a new vuart console type to xenconsole client
  xen/arm: vpl011: Add a pl011 uart DT node in the guest device tree
  xen/arm: vpl011: Update documentation for vuart console support

 docs/man/xl.cfg.pod.5.in             |   9 +
 docs/misc/console.txt                |  31 +-
 tools/console/client/main.c          |   8 +-
 tools/console/daemon/io.c            | 679 +++++++++++++++++++++++++----------
 tools/libxc/include/xc_dom.h         |   2 +
 tools/libxc/include/xenctrl.h        |  26 ++
 tools/libxc/xc_dom_arm.c             |   5 +-
 tools/libxc/xc_dom_boot.c            |   2 +
 tools/libxc/xc_domain.c              |  38 ++
 tools/libxl/libxl.h                  |   6 +
 tools/libxl/libxl_arm.c              |  53 ++-
 tools/libxl/libxl_console.c          |  36 ++
 tools/libxl/libxl_create.c           |  26 +-
 tools/libxl/libxl_device.c           |  45 ++-
 tools/libxl/libxl_dom.c              |  10 +
 tools/libxl/libxl_domain.c           |   2 +
 tools/libxl/libxl_internal.h         |   7 +
 tools/libxl/libxl_types.idl          |   7 +
 tools/libxl/libxl_types_internal.idl |   1 +
 tools/xl/xl_console.c                |   4 +-
 tools/xl/xl_parse.c                  |   8 +
 xen/arch/arm/Kconfig                 |   5 +
 xen/arch/arm/Makefile                |   1 +
 xen/arch/arm/domctl.c                |  27 ++
 xen/arch/arm/vgic-v2.c               |  28 +-
 xen/arch/arm/vgic-v3.c               |  40 +--
 xen/arch/arm/vpl011.c                | 350 ++++++++++++++++++
 xen/include/asm-arm/domain.h         |   6 +
 xen/include/asm-arm/pl011-uart.h     |   2 +
 xen/include/asm-arm/vgic.h           | 111 +-----
 xen/include/asm-arm/vpl011.h         |  94 +++++
 xen/include/asm-arm/vreg.h           | 109 ++++++
 xen/include/public/arch-arm.h        |   8 +
 xen/include/public/domctl.h          |  13 +
 34 files changed, 1439 insertions(+), 360 deletions(-)
 create mode 100644 xen/arch/arm/vpl011.c
 create mode 100644 xen/include/asm-arm/vpl011.h


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