Add a documentation file about the Timer/Counter Unit (TCU) present in
the Ingenic JZ47xx SoCs.
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 JZ4770 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.
Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
Tested-by: Mathieu Malaterre <malat@xxxxxxxxxx>
Tested-by: Artur Rojek <contact@xxxxxxxxxxxxxx>
---
Documentation/mips/ingenic-tcu.txt | 60 ++++++++++++++++++++++++++++++++++++++
1 file changed, 60 insertions(+)
create mode 100644 Documentation/mips/ingenic-tcu.txt
diff --git a/Documentation/mips/ingenic-tcu.txt b/Documentation/mips/ingenic-tcu.txt
new file mode 100644
index 000000000000..0ea35b2a46da
--- /dev/null
+++ b/Documentation/mips/ingenic-tcu.txt
@@ -0,0 +1,60 @@
+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 JZ4770 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.
+
+Implementation
+--------------
+
+The functionalities of the TCU hardware are spread across multiple drivers:
+- clocks/irq/timer: drivers/clocksource/ingenic-timer.c
+- PWM: drivers/pwm/pwm-jz4740.c
+- watchdog: drivers/watchdog/jz4740_wdt.c
+- OST: drivers/clocksource/ingenic-ost.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.
--
2.11.0
