[PATCH v2 0/4] mailbox: Improve the mbox core then introduce the goog-mba driver

[Douglas Anderson <dianders@chromium.org>]

The goal of this series is to land support for the goog-mba (MailBox
Array) IP block that's present in Pixel 10 phones.

As can be seen in the device-tree bindings for the goog-mba IP block,
the mailbox IP block in Pixel 10 phones is fairly sophisticated.
Notably:
* It has hardware features that support queuing, meaning that more
  than one mailbox message can be pending at a time.
* The "channels" in a given mailbox array aren't homogeneous. Each
  "channel" in the mailbox array can have a different amount of memory
  for messages. Really, the "channels" in a mailbox are considered to
  be full single-channel mailboxes and a grouping of mailboxes is
  considered a "mailbox array" (hence the IP block being named "mba")

In order to cleanly support `goog-mba`, improvements are made to the
mailbox core to allow `#mbox-cells = <0>` without a custom xlate and
to allow mailbox drivers that have more than one sub-node (`fwnode`).
For TX queue mode, as suggested in v1 review, `goog-mba` exposes each
hardware queue slot as a virtual mailbox channel rather than adding
queueing support to the mailbox core.

This is a fairly big rewrite from the downstream MBA driver shipping
on Pixel 10 phones, which jumped through some awkward hoops because of
the way it got queuing to work. It has been tested on a Pixel 10 Pro
XL (Mustang) together with work-in-progress Laguna CPM, pinctrl, PCIe,
and RTC drivers.

Link to previous versions:
v1: https://lore.kernel.org/r/20260714222338.2965707-1-dianders@chromium.org/

Changes in v2:
- Rename binding file to google,lga-mailbox-array.yaml.
- Drop generic "google,mailbox-array" fallback compatible.
- Add "google,tx-payload-words" property for queue-mode TX message size.
- Remove unused labels in DT example.
- Drop "dt-bindings: mailbox: Don't require #mbox-cells to be 1"
  (handled by deleting old mailbox.txt and updating dt-schema).
- Drop "mailbox: Simplify circular queue math with mod arithmetic" and
  "mailbox: Add support for mailbox controllers that can queue".
- Expose a mailbox channel per TX queue slot instead of adding
  `has_queue` to the mailbox core.
- For queue mode, read `google,tx-payload-words` from DT instead of
  detecting TX payload size on the first transfer.
- Match "google,lga-mailbox-array" instead of "google,mailbox-array".
- Move MAINTAINERS entries under GOOGLE TENSOR SoC SUPPORT.
- Use guard(spinlock_irqsave) and scoped_guard(spinlock).

Douglas Anderson (4):
  mailbox: Allow #mbox-cells = <0> without specifying a custom xlate
  mailbox: Find a matching mailbox by fwnode rather than device
  dt-bindings: mailbox: goog-mba: Add goog-mba mailbox bindings
  mailbox: goog-mba: Introduce the goog-mba mailbox driver

 .../mailbox/google,lga-mailbox-array.yaml     | 226 +++++++
 MAINTAINERS                                   |   3 +
 drivers/mailbox/Kconfig                       |   8 +
 drivers/mailbox/Makefile                      |   2 +
 drivers/mailbox/goog-mba-priv.h               | 130 ++++
 drivers/mailbox/goog-mba-trace.h              | 183 ++++++
 drivers/mailbox/goog-mba.c                    | 621 ++++++++++++++++++
 drivers/mailbox/mailbox.c                     |  16 +-
 include/linux/mailbox/goog-mba-message.h      |  38 ++
 include/linux/mailbox_controller.h            |   4 +
 10 files changed, 1229 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/mailbox/google,lga-mailbox-array.yaml
 create mode 100644 drivers/mailbox/goog-mba-priv.h
 create mode 100644 drivers/mailbox/goog-mba-trace.h
 create mode 100644 drivers/mailbox/goog-mba.c
 create mode 100644 include/linux/mailbox/goog-mba-message.h

-- 
2.56.0.257.gf7497c7d27-goog