diff options
3 files changed, 83 insertions, 0 deletions
diff --git a/Documentation/index.rst b/Documentation/index.rst
index 70ae148ec980..87214feda41f 100644
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -143,6 +143,7 @@ implementation.
+ mips/index
diff --git a/Documentation/mips/index.rst b/Documentation/mips/index.rst
new file mode 100644
index 000000000000..321b4794f3b8
--- /dev/null
+++ b/Documentation/mips/index.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: GPL-2.0
+MIPS-specific Documentation
+.. toctree::
+ :maxdepth: 1
+ :numbered:
+ ingenic-tcu
diff --git a/Documentation/mips/ingenic-tcu.rst b/Documentation/mips/ingenic-tcu.rst
new file mode 100644
index 000000000000..c4ef4c45aade
--- /dev/null
+++ b/Documentation/mips/ingenic-tcu.rst
@@ -0,0 +1,71 @@
+.. SPDX-License-Identifier: GPL-2.0
+Ingenic JZ47xx SoCs Timer/Counter Unit hardware
+The Timer/Counter Unit (TCU) in Ingenic JZ47xx SoCs is a multi-function
+hardware block. It features up to to eight channels, that can be used as
+counters, timers, or PWM.
+- JZ4725B, JZ4750, JZ4755 only have six TCU channels. The other SoCs all
+ have eight channels.
+- JZ4725B introduced a separate channel, called Operating System Timer
+ (OST). It is a 32-bit programmable timer. On JZ4760B and above, it is
+ 64-bit.
+- Each one of the TCU channels has its own clock, which can be reparented to three
+ different clocks (pclk, ext, rtc), gated, and reclocked, through their TCSR register.
+ - The watchdog and OST hardware blocks also feature a TCSR register with the same
+ format in their register space.
+ - The TCU registers used to gate/ungate can also gate/ungate the watchdog and
+ OST clocks.
+- Each TCU channel works in one of two modes:
+ - mode TCU1: channels cannot work in sleep mode, but are easier to
+ operate.
+ - mode TCU2: channels can work in sleep mode, but the operation is a bit
+ more complicated than with TCU1 channels.
+- The mode of each TCU channel depends on the SoC used:
+ - On the oldest SoCs (up to JZ4740), all of the eight channels operate in
+ TCU1 mode.
+ - On JZ4725B, channel 5 operates as TCU2, the others operate as TCU1.
+ - On newest SoCs (JZ4750 and above), channels 1-2 operate as TCU2, the
+ others operate as TCU1.
+- Each channel can generate an interrupt. Some channels share an interrupt
+ line, some don't, and this changes between SoC versions:
+ - on older SoCs (JZ4740 and below), channel 0 and channel 1 have their
+ own interrupt line; channels 2-7 share the last interrupt line.
+ - On JZ4725B, channel 0 has its own interrupt; channels 1-5 share one
+ interrupt line; the OST uses the last interrupt line.
+ - on newer SoCs (JZ4750 and above), channel 5 has its own interrupt;
+ channels 0-4 and (if eight channels) 6-7 all share one interrupt line;
+ the OST uses the last interrupt line.
+The functionalities of the TCU hardware are spread across multiple drivers:
+=========== =====
+clocks drivers/clk/ingenic/tcu.c
+interrupts drivers/irqchip/irq-ingenic-tcu.c
+timers drivers/clocksource/ingenic-timer.c
+OST drivers/clocksource/ingenic-ost.c
+PWM drivers/pwm/pwm-jz4740.c
+watchdog drivers/watchdog/jz4740_wdt.c
+=========== =====
+Because various functionalities of the TCU that belong to different drivers
+and frameworks can be controlled from the same registers, all of these
+drivers access their registers through the same regmap.
+For more information regarding the devicetree bindings of the TCU drivers,
+have a look at Documentation/devicetree/bindings/mfd/ingenic,tcu.txt.