Merge tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrlgrafted

Pull pin control updates from Linus Walleij:
 "Core changes:

   - Use the non-blocking mux_state_try_select() in the generic MUX pin
     control back-end

   - Free pin maps on pinctrl_generic_to_map() failure in the core
     helpers

  New hardware pin control:

   - Qualcomm Maili TLMM SoC, PMG1110 PMIC, and Eliza LPASS LPI TLMM SoC
     (this is for the low power audio, LPASS = Low Power Audio SubSystem
     portions)

   - Upboard support on top of the Intel pin controller

   - Apple T6030 and T6031 support (just compatible strings)

   - Samsung Exynos 8855 SoC

   - Mediatek MT6858 SoC

   - Rockchip RK3308B and RV1106 SoCs

   - Airoha EN7523 and AN7563 SoCs

  Improvements:

   - Qualcomm TLMM GPIOs are unconditionally marked as wakeup capable

   - Qualcomm improvements on top of the Qualcomm PDC (power domain
     controller) irqchip improvements from tglx:s tree

   - Qualcomm IPQ806x and IPQ9650 non-urgent pin grop fixups

   - The NPCM8xx driver has been put into shape fixing many pin and
     group definitions

   - Some non-urgent Tegra 264 pin assignments are fixed up

   - Some non-urgent fixups to Airoha AN7581 and AN7583 registers and
     pin assignments, missing features etc"

* tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl: (130 commits)
  dt-bindings: pinctrl: Convert TI DA850 pupd to DT schema
  pinctrl: meson: sync some modify from A4
  pinctrl: meson: a4: Add input enable pin configuration
  pinctrl: realtek: rtd1625: remove unused group name spdif_sel
  pinctrl: realtek: rtd1625: fix base_bit for VE4 GPIO 13
  dt-bindings: pinctrl: microchip,pic32mzda-pinctrl: Convert to DT schema
  Revert "Merge branch 'ib-rsk7204' into devel"
  pinctrl: rockchip: Add RV1106 pinctrl support
  dt-bindings: pinctrl: rockchip: Add RV1106 compatible
  pinctrl: rockchip: Decode drive strength in the get function
  pinctrl: fix PINCTRL_GENERIC_MUX not always being selectable
  pinctrl: airoha: add support of an7563 SoC
  dt-bindings: pinctrl: airoha: add support of an7563 pin controller
  pinctrl: airoha: try to find chip scu node by phandle first
  pinctrl: airoha: add support of en7523 SoC
  dt-bindings: pinctrl: airoha: add support of en7523 pin controller
  pinctrl: airoha: an7583: add support for olt pinmux
  pinctrl: airoha: an7583: add support for pon_alt pinmux
  pinctrl: airoha: an7583: add support for npu_uart pinmux
  dt-bindings: pinctrl: airoha: an7583: add missed features
  ...

1 files changed, 145 insertions, 0 deletions

diff --git a/Documentation/driver-api/virtio/virtio.rst b/Documentation/driver-api/virtio/virtio.rst
new file mode 100644
index 000000000..7947b4ca6
--- /dev/null
+++ b/Documentation/driver-api/virtio/virtio.rst
@@ -0,0 +1,145 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _virtio:
+
+===============
+Virtio on Linux
+===============
+
+Introduction
+============
+
+Virtio is an open standard that defines a protocol for communication
+between drivers and devices of different types, see Chapter 5 ("Device
+Types") of the virtio spec (`[1]`_). Originally developed as a standard
+for paravirtualized devices implemented by a hypervisor, it can be used
+to interface any compliant device (real or emulated) with a driver.
+
+For illustrative purposes, this document will focus on the common case
+of a Linux kernel running in a virtual machine and using paravirtualized
+devices provided by the hypervisor, which exposes them as virtio devices
+via standard mechanisms such as PCI.
+
+
+Device - Driver communication: virtqueues
+=========================================
+
+Although the virtio devices are really an abstraction layer in the
+hypervisor, they're exposed to the guest as if they are physical devices
+using a specific transport method -- PCI, MMIO or CCW -- that is
+orthogonal to the device itself. The virtio spec defines these transport
+methods in detail, including device discovery, capabilities and
+interrupt handling.
+
+The communication between the driver in the guest OS and the device in
+the hypervisor is done through shared memory (that's what makes virtio
+devices so efficient) using specialized data structures called
+virtqueues, which are actually ring buffers [#f1]_ of buffer descriptors
+similar to the ones used in a network device:
+
+.. kernel-doc:: include/uapi/linux/virtio_ring.h
+    :identifiers: struct vring_desc
+
+All the buffers the descriptors point to are allocated by the guest and
+used by the host either for reading or for writing but not for both.
+
+Refer to Chapter 2.5 ("Virtqueues") of the virtio spec (`[1]`_) for the
+reference definitions of virtqueues and "Virtqueues and virtio ring: How
+the data travels" blog post (`[2]`_) for an illustrated overview of how
+the host device and the guest driver communicate.
+
+The :c:type:`vring_virtqueue` struct models a virtqueue, including the
+ring buffers and management data. Embedded in this struct is the
+:c:type:`virtqueue` struct, which is the data structure that's
+ultimately used by virtio drivers:
+
+.. kernel-doc:: include/linux/virtio.h
+    :identifiers: struct virtqueue
+
+The callback function pointed by this struct is triggered when the
+device has consumed the buffers provided by the driver. More
+specifically, the trigger will be an interrupt issued by the hypervisor
+(see vring_interrupt()). Interrupt request handlers are registered for
+a virtqueue during the virtqueue setup process (transport-specific).
+
+.. kernel-doc:: drivers/virtio/virtio_ring.c
+    :identifiers: vring_interrupt
+
+
+Device discovery and probing
+============================
+
+In the kernel, the virtio core contains the virtio bus driver and
+transport-specific drivers like `virtio-pci` and `virtio-mmio`. Then
+there are individual virtio drivers for specific device types that are
+registered to the virtio bus driver.
+
+How a virtio device is found and configured by the kernel depends on how
+the hypervisor defines it. Taking the `QEMU virtio-console
+<https://gitlab.com/qemu-project/qemu/-/blob/master/hw/char/virtio-console.c>`__
+device as an example. When using PCI as a transport method, the device
+will present itself on the PCI bus with vendor 0x1af4 (Red Hat, Inc.)
+and device id 0x1003 (virtio console), as defined in the spec, so the
+kernel will detect it as it would do with any other PCI device.
+
+During the PCI enumeration process, if a device is found to match the
+virtio-pci driver (according to the virtio-pci device table, any PCI
+device with vendor id = 0x1af4)::
+
+	/* Qumranet donated their vendor ID for devices 0x1000 thru 0x10FF. */
+	static const struct pci_device_id virtio_pci_id_table[] = {
+		{ PCI_DEVICE(PCI_VENDOR_ID_REDHAT_QUMRANET, PCI_ANY_ID) },
+		{ 0 }
+	};
+
+then the virtio-pci driver is probed and, if the probing goes well, the
+device is registered to the virtio bus::
+
+	static int virtio_pci_probe(struct pci_dev *pci_dev,
+				    const struct pci_device_id *id)
+	{
+		...
+
+		if (force_legacy) {
+			rc = virtio_pci_legacy_probe(vp_dev);
+			/* Also try modern mode if we can't map BAR0 (no IO space). */
+			if (rc == -ENODEV || rc == -ENOMEM)
+				rc = virtio_pci_modern_probe(vp_dev);
+			if (rc)
+				goto err_probe;
+		} else {
+			rc = virtio_pci_modern_probe(vp_dev);
+			if (rc == -ENODEV)
+				rc = virtio_pci_legacy_probe(vp_dev);
+			if (rc)
+				goto err_probe;
+		}
+
+		...
+
+		rc = register_virtio_device(&vp_dev->vdev);
+
+When the device is registered to the virtio bus the kernel will look
+for a driver in the bus that can handle the device and call that
+driver's ``probe`` method.
+
+At this point, the virtqueues will be allocated and configured by
+calling the appropriate ``virtio_find`` helper function, such as
+virtio_find_single_vq() or virtio_find_vqs(), which will end up calling
+a transport-specific ``find_vqs`` method.
+
+
+References
+==========
+
+_`[1]` Virtio Spec v1.2:
+https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
+
+.. Check for later versions of the spec as well.
+
+_`[2]` Virtqueues and virtio ring: How the data travels
+https://www.redhat.com/en/blog/virtqueues-and-virtio-ring-how-data-travels
+
+.. rubric:: Footnotes
+
+.. [#f1] that's why they may be also referred to as virtrings.