[PATCH v5 03/21] doc: Add doc for the Ingenic TCU hardware

Paul Cercueil
2018-07-24T23:20:21Z

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 64-bit programmable timer.

- 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@crapouillou.net>
---
Documentation/mips/00-INDEX | 3 ++
Documentation/mips/ingenic-tcu.txt | 59 ++++++++++++++++++++++++++++++++++++++
2 files changed, 62 insertions(+)
create mode 100644 Documentation/mips/ingenic-tcu.txt

v4: New patch in this series

v5: Added information about number of channels, and improved
documentation about channel modes

diff --git a/Documentation/mips/00-INDEX b/Documentation/mips/00-INDEX
index 8ae9cffc2262..8ab8c3f83771 100644
--- a/Documentation/mips/00-INDEX
+++ b/Documentation/mips/00-INDEX
@@ -2,3 +2,6 @@
- this file.
AU1xxx_IDE.README
- README for MIPS AU1XXX IDE driver.
+ingenic-tcu.txt
+ - Information file about the Timer/Counter Unit present
+ in Ingenic JZ47xx SoCs.
diff --git a/Documentation/mips/ingenic-tcu.txt b/Documentation/mips/ingenic-tcu.txt
new file mode 100644
index 000000000000..dd044c40dbfe
--- /dev/null
+++ b/Documentation/mips/ingenic-tcu.txt
@@ -0,0 +1,59 @@
+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 64-bit programmable timer.
+
+- 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