Merge tag 'hw-misc-20241231' of https://github.com/philmd/qemu into staging

Misc HW patches queue

- Allow more than 4 legacy IRQs on Generic PCI Express Bridge (Alexander)
- Add MMIO-based Inter-VM shared memory device 'ivshmem-flat' (Gustavo)
- Use UHCI register definitions (Guenter)
- Propagate CPU endianness to microblaze_load_kernel (Philippe)
- Mark x86/TriCore devices as little-endian, OpenRISC/SPARC as big (Philippe)
- Don't set callback_opaque NULL in fw_cfg_modify_bytes_read (Shameer)
- Simplify non-KVM checks on AMD IOMMU XTSup feature (Philippe)
- Trivial cleanups on xilinx_ethlite, vmcoreinfo, qxl (Philippe, Hyman)
- Move USB-HCD-XHCI msi/msix properties from NEC to superclass (Phil)
- Redesign of main thread event handling due to macOS Cocoa (Phil)
- Introduce ParavirtualizedGraphics.Framework support 'apple-gfx' (Phil)
- Pad short Ethernet frames on macOS vmnet (William)

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* tag 'hw-misc-20241231' of https://github.com/philmd/qemu: (29 commits)
  hw/display/qxl: Do not use C99 // comments
  net/vmnet: Pad short Ethernet frames
  MAINTAINERS: Add myself as maintainer for apple-gfx, reviewer for HVF
  hw/display/apple-gfx: Adds configurable mode list
  hw/display/apple-gfx: Adds PCI implementation
  hw/display/apple-gfx: Introduce ParavirtualizedGraphics.Framework support
  ui & main loop: Redesign of system-specific main thread event handling
  hw/usb/hcd-xhci: Unimplemented/guest error logging for port MMIO
  hw/usb/hcd-xhci-pci: Move msi/msix properties from NEC to superclass
  hw/block/virtio-blk: Replaces request free function with g_free
  hw/i386/amd_iommu: Simplify non-KVM checks on XTSup feature
  hw/misc/vmcoreinfo: Rename opaque pointer as 'opaque'
  hw/misc/vmcoreinfo: Declare QOM type using DEFINE_TYPES macro
  fw_cfg: Don't set callback_opaque NULL in fw_cfg_modify_bytes_read()
  hw/net/xilinx_ethlite: Rename rxbuf -> port_index
  hw/net/xilinx_ethlite: Correct maximum RX buffer size
  hw/net/xilinx_ethlite: Update QOM style
  hw/net/xilinx_ethlite: Remove unuseful debug logs
  hw/net/xilinx_ethlite: Convert some debug logs to trace events
  hw/sparc: Mark devices as big-endian
  ...

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/docs/system/device-emulation.rst b/docs/system/device-emulation.rst
index f197774..a1b0d79 100644
--- a/docs/system/device-emulation.rst
+++ b/docs/system/device-emulation.rst
@@ -86,6 +86,7 @@ Emulated Devices
    devices/ccid.rst
    devices/cxl.rst
    devices/ivshmem.rst
+   devices/ivshmem-flat.rst
    devices/keyboard.rst
    devices/net.rst
    devices/nvme.rst
diff --git a/docs/system/devices/ivshmem-flat.rst b/docs/system/devices/ivshmem-flat.rst
new file mode 100644
index 0000000..1f97052
--- /dev/null
+++ b/docs/system/devices/ivshmem-flat.rst
@@ -0,0 +1,33 @@
+Inter-VM Shared Memory Flat Device
+----------------------------------
+
+The ivshmem-flat device is meant to be used on machines that lack a PCI bus,
+making them unsuitable for the use of the traditional ivshmem device modeled as
+a PCI device. Machines like those with a Cortex-M MCU are good candidates to use
+the ivshmem-flat device. Also, since the flat version maps the control and
+status registers directly to the memory, it requires a quite tiny "device
+driver" to interact with other VMs, which is useful in some RTOSes, like
+Zephyr, which usually run on constrained resource targets.
+
+Similar to the ivshmem device, the ivshmem-flat device supports both peer
+notification via HW interrupts and Inter-VM shared memory. This allows the
+device to be used together with the traditional ivshmem, enabling communication
+between, for instance, an aarch64 VM  (using the traditional ivshmem device and
+running Linux), and an arm VM (using the ivshmem-flat device and running Zephyr
+instead).
+
+The ivshmem-flat device does not support the use of a ``memdev`` option (see
+ivshmem.rst for more details). It relies on the ivshmem server to create and
+distribute the proper shared memory file descriptor and the eventfd(s) to notify
+(interrupt) the peers. Therefore, to use this device, it is always necessary to
+have an ivshmem server up and running for proper device creation.
+
+Although the ivshmem-flat supports both peer notification (interrupts) and
+shared memory, the interrupt mechanism is optional. If no input IRQ is
+specified for the device it is disabled, preventing the VM from notifying or
+being notified by other VMs (a warning will be displayed to the user to inform
+the IRQ mechanism is disabled). The shared memory region is always present.
+
+The MMRs (INTRMASK, INTRSTATUS, IVPOSITION, and DOORBELL registers) offsets at
+the MMR region, and their functions, follow the ivshmem spec, so they work
+exactly as in the ivshmem PCI device (see ./specs/ivshmem-spec.txt).