[PATCH v3 0/4] xen/arm: add i.MX8M platform and UART support

[Wig Cheng <onlywig@gmail.com>]

Following Michal Orzel's review of v2, this series adds Xen support for
the NXP i.MX8M family (i.MX8MP / MQ / MM / MN).  It provides the console
UART driver, its early printk, the platform glue (SiP SMC whitelist for
the calls the dom0 kernel issues to TF-A), and a MAINTAINERS entry.

Tested on i.MX8MP (4x Cortex-A53, GICv3) with the vendor kernel 6.18:
dom0 boots to login on the hypervisor console, and a domU starts with a
PV disk and virtio devices running a full Wayland distro.

Notes for reviewers:

- Unlike i.MX8MQ, the i.MX8MP device tree uses the GIC as the root
  interrupt controller (interrupt-parent = <&gic>), so no device-tree
  workaround is needed and power domains keep working.

- The i.MX8M family has no SMMU, so device passthrough relies on the
  1:1 direct-mapped hardware domain.

- The SiP SMC whitelist forwards only the specific subfunctions the
  dom0 kernel issues, extracted from the vendor kernel call sites.
  Following the v2 review, CPU and DRAM frequency scaling are now both
  denied: the hardware domain cannot make an informed decision about
  resources it shares with the other domains.  dom0's i.MX8M DDRC
  devfreq driver issues the DDR DVFS call at boot; with it denied that
  driver just skips DRAM frequency scaling (the DRAM stays at the
  frequency set by firmware) and dom0 boots normally.

Changes since v2:

Patch 1 (UART driver):
- Add imx-uart.c to the Arm MAINTAINERS section so it falls under Arm
  maintainership.
- Gate serial_tx_interrupt() on TRDYEN; USR1_TRDY is a raw status bit,
  set independently of whether the TX interrupt is enabled.
- Print the IRQ number with %u.

Patch 2 (early printk):
- No code changes; picked up Michal's Reviewed-by.

Patch 3 (platform):
- Include <asm/regs.h> for get/set_user_reg().
- Add a description for the CPUFREQ function id.
- Drop the unused SRC M4_START and NoC LCDIF subfunction macros.
- Order the switch cases by function id.
- Deny DDR DVFS as well as CPU frequency scaling (same reasoning),
  rather than forwarding it.
- Return false directly on a denied subfunction instead of goto plus a
  redundant printk.

Patch 4 (MAINTAINERS):
- No changes; picked up Michal's Reviewed-by.

v2: https://lore.kernel.org/xen-devel/20260818025224.4165503-1-onlywig@gmail.com/

Wig Cheng (4):
  xen/char: add classic i.MX UART driver
  xen/arm64: add early printk for the classic i.MX UART
  xen/arm: add i.MX8M platform support
  MAINTAINERS: add myself as reviewer of i.MX8M related patches

 MAINTAINERS                           |   8 +
 xen/arch/arm/Kconfig.debug            |  12 ++
 xen/arch/arm/arm64/debug-imx-uart.inc |  37 ++++
 xen/arch/arm/include/asm/imx-uart.h   |  57 +++++++
 xen/arch/arm/platforms/Makefile       |   1 +
 xen/arch/arm/platforms/imx8m.c        | 139 +++++++++++++++
 xen/drivers/char/Kconfig              |   8 +
 xen/drivers/char/Makefile             |   1 +
 xen/drivers/char/imx-uart.c           | 233 ++++++++++++++++++++++++++
 9 files changed, 496 insertions(+)
 create mode 100644 xen/arch/arm/arm64/debug-imx-uart.inc
 create mode 100644 xen/arch/arm/include/asm/imx-uart.h
 create mode 100644 xen/arch/arm/platforms/imx8m.c
 create mode 100644 xen/drivers/char/imx-uart.c

-- 
2.43.0