Hi,
The imx6ull.dtsi file in the linux kernel, there exists the following section:
pwm5: pwm@020f0000 {
compatible = "fsl,imx6ul-pwm", "fsl,imx27-pwm";
reg = <0x020f0000 0x4000>;
interrupts = <GIC_SPI 114 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clks IMX6UL_CLK_DUMMY>,
<&clks IMX6UL_CLK_DUMMY>;
clock-names = "ipg", "per";
#pwm-cells = <2>;
};
While in the imx6ul.dtsi, this looks like this:
pwm5: pwm@020f0000 {
compatible = "fsl,imx6ul-pwm", "fsl,imx27-pwm";
reg = <0x020f0000 0x4000>;
interrupts = <GIC_SPI 114 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clks IMX6UL_CLK_PWM5>,
<&clks IMX6UL_CLK_PWM5>;
clock-names = "ipg", "per";
#pwm-cells = <2>;
status = "disabled";
};
I do not understand why many pwm clocks are missing in the ULL device tree.
As can be seen on the datasheet from the ULL (https://www.nxp.com/docs/en/data-sheet/IMX6ULLCEC.pdf), there are versions that have to support the 8 PWM's.
Note that the effect of not putting this in the imx6ull.dtsi, is that without explicitly configuring them in the upper device tree:
- The relevant PWM clock will be disabled by linux at the end of the boot process (disable_unused_clocks) (unless the clk_ignore_unused flag in the cmdline is passed)
- If the pwm was activated at boot, any subsequent change (e.g. through sysfs, or even at reboot) will cause a read from the hardware control register of the unclocked periperhal. This completely freezes the CPU.
The current workaround I have to use in my own board's dts file is:
&pwm5 {
pinctrl-names = "default";
clocks = <&clks IMX6UL_CLK_PWM5>,
<&clks IMX6UL_CLK_PWM5>;
clock-names = "ipg", "per";
pinctrl-0 = <&pinctrl_pwm5>;
status = "okay";
};
I hope this gets fixed soon, so that nobody else bumps into this unexpected issue
