tty/serial: meson_uart: add support for core clock handling

This patchset is a re-spin of Helmut Klein's v3 patchset at [0] and the v4 patchset at [1].

Initially, the original patchset was made to enable usage on the non-AO UARTS not enabled by the Bootloader (uart_B and uart_C), but the patchset needed an overall change to have clean and stable DT bindings.

The Amlogic Meson UART Driver did not have stable DT bindings and mismatched clock handling on non-AO UARTs since these "EE" UARTs needs a clock gate to be ungated to works correctly.
In the same way, the AO UARTs does not need gating and can be used as Early Consoles.

In the same time, the UART Interfaces can take clock input for the baudrate generate from either the external Xtal or the internal Bus Clock (clk81).

So new bindings was necessary to meet these requirements and the DT maintainers requirements.

The "legacy" binding actually used in the driver is left until all the DT files are switched to the new bindings.

The GX DT has been tested, but the last 4 Meson6/Meson8/b are only compile-tested, and testing is welcome.
Thus only the first 3 patches can be merged until the Meson6/Meson8/b are formally tested.

It must be noted that the meson6 cannot work today except using an early console since the UART driver could not probe without a clocks property.

Changes since v4 at [1]:
- Droped meson8/meson8b DT patches
- Fixes copy/paste error in patch 2
- Refactored clock probing in patch 2
- merged meson6 patches together to avoid breaking bisect

[0] http://lkml.kernel.org/r/20170331165437.26227-1-hgkr.klein at gmail.com
[1] http://lkml.kernel.org/r/1497001756-942-1-git-send-email-narmstrong at baylibre.com

Helmut Klein (3):
dt-bindings: serial: Add bindings for the Amlogic Meson UARTs tty/serial: meson_uart: update to stable bindings
ARM64: dts: meson-gx: use stable UART bindings with correct gate clock

Neil Armstrong (1):
ARM: dts: meson6: use stable UART bindings

 .../bindings/serial/amlogic,meson-uart.txt         | 38 +++++++++
 arch/arm/boot/dts/meson.dtsi                       |  8 +-
 arch/arm/boot/dts/meson6.dtsi                      | 28 +++++++
 arch/arm64/boot/dts/amlogic/meson-gx.dtsi          | 12 ++-
 arch/arm64/boot/dts/amlogic/meson-gxbb.dtsi        | 25 ++++++
 arch/arm64/boot/dts/amlogic/meson-gxl.dtsi         | 25 ++++++
 drivers/tty/serial/meson_uart.c                    | 90 ++++++++++++++++++++--
 7 files changed, 209 insertions(+), 17 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/serial/amlogic,meson-uart.txt

1.9.1