The T-head TH1520 SoC supports a hardware mailbox that enables two cores
within the SoC to communicate and coordinate [1]. One example of such
coordination would be cooperation with the T-Head E902 core, which is
responsible for power, clock, and resource management. For example, in
the specific case of the BXM-4-64 GPU, it needs to be powered on by the
E902 core, and the kernel running on the E910 needs to 'ask' the
firmware running on the E902 core to enable power to the GPU island.
Given recent advancements in work on the upstream GPU driver [2], there
is an emerging need to get this code in the mainline kernel.

Link: https://openbeagle.org/beaglev-ahead/beaglev-ahead/-/blob/main/docs/TH1520%20System%20User%20Manual.pdf [1]
Link: https://gitlab.freedesktop.org/imagination/linux-firmware/-/issues/1 [2]

Thanks, Krzysztof and Rob, for your review! Since this series is gaining
some interest, I'm dropping the RFC prefix with this v3 update.

v3:
- added a comment about mixing devm_ and non-devm resources in the context
  of shared interrupts and explained why it's safe to do so in this
  particular case
- changed the order of resource freeing in the .shutdown callback
- used a wrapper function for register mapping
- since the only conceivable use case for this mailbox driver is
  communication with cores not managed by the kernel, I’ve hard-coded
  this by removing the thead,icu-cpu-id property and adjusted the mailbox
  driver code accordingly.
- added a more detailed description for mbox-cells.
- made some cosmetic changes.
- retested by applying the patch with non-yet-upstreamed patches,
  confirming that the drm/imagination driver can read the registers
  correctly.

v2:
 - fixed thead,th1520-mbox.yaml binding file by dropping redundant
   descriptions, renaming reg-names, removing unnecessary clocks,
   providing constraints and defining ICU's
 - fixed the mailbox driver code to work well with updated binding-file,
   removed clocks support, as it's not necessary for mailbox to work
 - adjusted the device tree node instance of mbox_910t so it will work
   with updated bindings file

Michal Wilczynski (3):
  mailbox: Introduce support for T-head TH1520 Mailbox driver
  dt-bindings: mailbox: Add thead,th1520-mailbox bindings
  riscv: dts: thead: Add mailbox node

 .../bindings/mailbox/thead,th1520-mbox.yaml   |  81 +++
 MAINTAINERS                                   |   2 +
 arch/riscv/boot/dts/thead/th1520.dtsi         |  12 +
 drivers/mailbox/Kconfig                       |  10 +
 drivers/mailbox/Makefile                      |   2 +
 drivers/mailbox/mailbox-th1520.c              | 576 ++++++++++++++++++
 6 files changed, 683 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml
 create mode 100644 drivers/mailbox/mailbox-th1520.c

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2.34.1