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feat: Linux: drivers: Add initial DM-Timer documentation #152
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137 changes: 137 additions & 0 deletions
137
source/linux/Foundational_Components/Kernel/Kernel_Drivers/DM-Timer.rst
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| ######## | ||
| DM TIMER | ||
| ######## | ||
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| - This guide covers a general overview on DM Timer, it supports DM Timers found on TI's | ||
| |__PART_FAMILY_NAME__| SoC. | ||
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| - Each timer comes with dedicated pins that can be used as timer capture inputs or as timer | ||
| PWM outputs, please check the device TRM for more information. | ||
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| - Each timer contains a free-running upward counter with autoreload capability on overflow. | ||
| Each timer includes compare logic to allow an interrupt event on a programmable counter | ||
| matching value. A dedicated output signal can be pulsed/toggled on an overflow or a match | ||
| event. This offers time-stamp trigger signaling or PWM signal sources. A dedicated input | ||
| signal can be used to trigger an automatic timer counter capture or an interrupt event on a | ||
| programmable input signal transition. | ||
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| - For more detailed information on timers, please refer to the: ``Peripherals/Timer Modules/Timers`` | ||
| section of the device specific TRM. | ||
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| ************** | ||
| Driver Sources | ||
| ************** | ||
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| - Driver source location: :file:`drivers/clocksource/ti,timer-dm.c` | ||
| - Binding source location: :file:`Documentation/device-tree/bindings/timer/ti,timer-dm.yaml` | ||
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| *Enabling PWM output signals:* | ||
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| - Driver source location: :file:`drivers/pwm/pwm-omap-dmtimer.c` | ||
| - Binding source location: :file:`Documentation/devicetree/bindings/pwm/pwm-omap-dmtimer.txt` | ||
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| ******************** | ||
| Kernel Configuration | ||
| ******************** | ||
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| Configs to be enabled in Linux Kernel: | ||
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| .. code-block:: menuconfig | ||
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| Device Drivers ---> | ||
| -> Clock Source drivers | ||
| -> OMAP dual-mode timer driver (OMAP_DM_TIMER [=y]) | ||
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| *Enabling PWM output signals:* | ||
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| .. code-block:: menuconfig | ||
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| Device Drivers ---> | ||
| Pulse-Width Modulation (PWM) Support (PWM [=y]) | ||
| -> OMAP Dual-Mode Timer PWM support (PWM_OMAP_DMTIMER [=m]) | ||
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| .. rubric:: DTS node for DM Timer | ||
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| In this example, we take am62x SK DT node as an example. In general all the timer nodes | ||
| should be described in its appropriate voltage domain .dtsi file, for example the following | ||
| node can be found in k3-am62-main.dtsi: | ||
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| .. code-block:: dts | ||
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| main_timer3: timer@2430000 { | ||
| compatible = "ti,am654-timer"; | ||
| reg = <0x00 0x2430000 0x00 0x400>; | ||
| interrupts = <GIC_SPI 123 IRQ_TYPE_LEVEL_HIGH>; | ||
| clocks = <&k3_clks 39 2>; | ||
| clock-names = "fck"; | ||
| assigned-clocks = <&k3_clks 39 2>; | ||
| assigned-clock-parents = <&k3_clks 39 3>; | ||
| power-domains = <&k3_pds 39 TI_SCI_PD_EXCLUSIVE>; | ||
| ti,timer-pwm; | ||
| }; | ||
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| *Enabling PWM output signals:* | ||
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| - The "ti,timer-pwm" DT attribute is required in the DM Timer node in order to enable PWM output | ||
| signals. | ||
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| An additional DT node is required in order to enable PWM output signals as shown below. The | ||
| ``main_timer3_pins_default`` is also required and not listed here, use sysconfig tool to get | ||
| pinumux configuration. | ||
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| .. code-block:: dts | ||
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| main_pwm3: dmtimer-main-pwm-3 { | ||
| compatible = "ti,omap-dmtimer-pwm"; | ||
| #pwm-cells = <3>; | ||
| ti,timers = <&main_timer3>; | ||
| pinctrl-names = "default"; | ||
| pinctrl-0 = <&main_timer3_pins_default>; | ||
| }; | ||
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| ************ | ||
| Driver Usage | ||
| ************ | ||
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| For information on using DM timer as a counter, please refer to the detailed descriptions | ||
| in the TRM ``Timers Functional Description`` and ``Low-Level Programming Models`` under | ||
| ``Peripherals/Timers Modules/Timers``. | ||
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| .. note:: | ||
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| Currently there is no sysfs interface to interact with the DM Timer as a counter via userspace. | ||
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| - Timers in "Timer" mode should be enabled by default in Linux DT. | ||
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| .. ifconfig:: CONFIG_part_variant in ('AM62X', 'AM62AX', 'AM62PX') | ||
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| In MAIN domain: | ||
| - 8 DM timers in MAIN domain | ||
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| In MCU domain: | ||
| - 4 DM timers in MCU domain | ||
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| .. ifconfig:: CONFIG_part_variant in ('AM64X') | ||
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| In MAIN domain: | ||
| - 12 DM timers in MAIN domain | ||
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| In MCU domain: | ||
| - 4 DM timers in MCU domain | ||
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| *Enabling PWM output signals:* | ||
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| If the PWM node exists in DT using a DM TIMER, the PWM device is probed and exposed as a | ||
| PWM device by Linux Kernel to be used by userspace in :file:`/sys/class/pwm`. | ||
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| For controlling the PWM chip via sysfs interface please refer to the official Linux | ||
| documentation: `here <https://docs.kernel.org/driver-api/pwm.html#using-pwms-with-the-sysfs-interface>`__ | ||
| or go to :ref:`Using-PWM-with-sysfs`. | ||
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| ******** | ||
| Examples | ||
| ******** | ||
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| To enable DM timer PWM output signals, there is an example DT overlay found in | ||
| :file:`arch/arm64/boot/dts/ti/k3-am62x-sk-dmtimer-pwm.dtso` that applies for am62x | ||
| family devices and can be referenced for other K3 devices. | ||
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