setup device-tree entry for ecap / pwmleds

I should add that we are using the 3.18.20 kernel.

progress or regression? made a few changes to the device tree entries, since it is based off of the evm, we use this include

#include "am33xx.dtsi"

updated DTS reads as follows:
----------
pwmleds {
compatible = "pwm-leds";

pmu_stat {
label = "ivee::pmu_stat";
pwms = <&ecap1 0 50000 1>;
max-brightness = <255>;
linux,default-trigger = "default-on";
brightness = <127>;
};
};
--------
ecap1_pins: ecap1_pins {
pinctrl-single,pins = <
0x160 ( PIN_OUTPUT | MUX_MODE2 ) /* (C15) spi0_cs1.eCAP1_in_PWM1_out */
>;
};
--------
&epwmss1 {
status = "okay";
ecap1: ecap@48302100 {
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <&ecap1_pins>;
};
};

Now we get these boot messages

[ 13.662966] leds_pwm pwmleds: unable to request PWM for ivee::pmu_stat: -517
[ 13.709080] platform pwmleds: Driver leds_pwm requests probe deferral

and the /sys/class/pwm/ is still empty

Hi Tom,

Have you verified the kernel configuration: processors.wiki.ti.com/.../AM335x_PWM_Driver's_Guide

Also you can refer to am335x-evm.dts or am335x-evmsk.dts to see how ecap is set.

Best Regards,
Yordan

Hi Yordan, Thanks for responding. Yes, I have reviewed a number of related documents including the PWM drivers guide in detail, however it doesn't outline DTS examples in any detail. I also have looked at the am335x-evm*.dts files, reviewed multiple related posts and tired a number of different DTS configurations. It just appears something is not enabled properly.

Can you please describe the configuration fields in

pwms = <&ecap1 0 50000 1>; 

and what function they apply to? Thanks, Tom

I was hoping to get some clarification on what the configuration fields mean... please advise. Thanks, Tom

Yordan, Yes, I've been over the documentation multiple times and have tried a number of different device tree approaches without any luck. Here is the latest of which the attempt was to create a backlight DT entry that will just output a PWM clock using ecap1. Can someone check the entry and perhaps see what I am doing wrong. BTW, both of the PWM based modules are built with the kernel config.

We started with an EVM-SK based DTS. Includes are

#include "am33xx.dtsi"
#include <dt-bindings/interrupt-controller/irq.h>
#include <dt-bindings/pwm/pwm.h>

* define the backlight and configure for ecap1

backlight {
compatible = "pwm-backlight";
pwms = <&ecap1 0 50000 1>;
brightness-levels = <0 58 61 66 75 90 125 170 255>;
default-brightness-level = <8>;
power-supply = <&vaux2_reg>;
};

* define the pin

ecap1_pins: ecap1_pins {
pinctrl-single,pins = <
0x160 ( PIN_OUTPUT | MUX_MODE2 ) /* (C15) spi0_cs1.eCAP1_in_PWM1_out */
>;
};

* define ecap1

&ecap1 {
status = "okay";
};

* this is the only related boot message received

[ 0.325186] platform backlight: Driver pwm-backlight requests probe deferral

I can't think of a more generic DTS entry, I have tried many other configurations based off of other DTS files with varying messages but I want to fallback to a very basic implementation. Please advise, Thanks, Tom

Hi Tom,

Sorry for the delayed response.

Can you try the following :

&epwmss1 {
status = "okay";
ecap1: ecap@0x48302100 {
status = "okay";
pinctrl-names = "default";
pinctrl-0 = "ecap1_pins";
};
};

Also add some prints in the probe functions in pwmss & ecap driver, to see if they pass.

Best Regards,
Yordan

Hi Yordan,

Thanks for responding, Here's the latest output with printfs

[    1.735749] pwm-backlight backlight: TR_DBG: pwm_backlight_probe entering...
[    1.743233] pwm-backlight backlight: GPIO lookup for consumer enable
[    1.743248] pwm-backlight backlight: using device tree for GPIO lookup
[    1.743266] of_get_named_gpiod_flags: can't parse 'enable-gpios' property of node '/backlight[0]'
[    1.743280] of_get_named_gpiod_flags: can't parse 'enable-gpio' property of node '/backlight[0]'
[    1.743294] pwm-backlight backlight: using lookup tables for GPIO lookup
[    1.743308] pwm-backlight backlight: lookup for GPIO enable failed
[    1.743321] pwm-backlight backlight: TR_DBG: pwm_backlight_probe enable_gpio...
[    1.751043] pwm-backlight backlight: TR_DBG: pwm_backlight_probe gpio direction ...
[    1.759124] pwm-backlight backlight: TR_DBG: pwm_backlight_probe get regulator...
[    1.767176] pwm-backlight backlight: TR_DBG: pwm_backlight_probe pwm_get...
[    1.774620] pwm-backlight backlight: TR_DBG: got pwm for backlight...
[    1.781445] pwm-backlight backlight: TR_DBG: get pwm_period ...
[    1.787699] pwm-backlight backlight: TR_DBG: lth_brightness ...
[    1.793935] pwm-backlight backlight: TR_DBG: backlight device register ...
[    1.801518] pwm-backlight backlight: TR_DBG: backlight device registered? 0xcdde8e00 ...
[    1.810316] pwm-backlight backlight: TR_DBG: done should be ok? 0xcdde8e00 ...

From what I can tell it completes the probe. I see the following in sys/class

root@am335x-evm:~# ls -ltrh /sys/class/pwm/
lrwxrwxrwx    1 root     root           0 Jan  1 00:00 pwmchip0 -> ../../devices/ocp/48302000.epwmss/48302100.ecap/pwm/pwmchip0
root@am335x-evm:~# ls -ltrh /sys/class/pwm/pwmchip0/
-rw-r--r--    1 root     root        4.0K Jan  1 00:00 uevent
lrwxrwxrwx    1 root     root           0 Jan  1 00:00 subsystem -> ../../../../../../class/pwm
--w-------    1 root     root        4.0K Jan  1 00:00 unexport
drwxr-xr-x    2 root     root           0 Jan  1 00:00 power
-r--r--r--    1 root     root        4.0K Jan  1 00:00 npwm
--w-------    1 root     root        4.0K Jan  1 00:00 export
lrwxrwxrwx    1 root     root           0 Jan  1 00:00 device -> ../../../48302100.ecap

However the instructions to enable the PWM on this link

http://processors.wiki.ti.com/index.php/AM335x_PWM_Driver%27s_Guide

do not seem to match up with the pwmchip0 that is in the pwm dir

Does this look correct? if so how do I enable it from user space. Thanks, Tom

Note: updated the DTS entries as follows:

    backlight {
        compatible = "pwm-backlight";
        pwms = <&ecap1 0 50000 1>;
        brightness-levels = <0 58 61 66 75 90 125 170 255>;
        default-brightness-level = <8>;
        power-supply = <&vaux2_reg>;

    };

&ecap1 {
    status = "okay";
};

&epwmss1 {
    status = "okay";
    ecap1: ecap@48302100 {
        status = "okay";
        pinctrl-names = "default";
        pinctrl-0 = <&ecap1_pins>;
    };
};

Hi Yordan,

Can you weigh in on what I',m seeing above in the sys/class. Does it make sense, if so how can I configure and test it. Thanks, Tom

Hi Yordan,

Can you possibly respond to the latest output I have listed below? I do not see a specific ecap device, just pwmchip0. Is this correct?


root@am335x-evm:~# ls -ltrh /sys/class/pwm/
lrwxrwxrwx 1 root root 0 Jan 1 00:00 pwmchip0 -> ../../devices/ocp/48302000.epwmss/48302100.ecap/pwm/pwmchip0
root@am335x-evm:~# ls -ltrh /sys/class/pwm/pwmchip0/
-rw-r--r-- 1 root root 4.0K Jan 1 00:00 uevent
lrwxrwxrwx 1 root root 0 Jan 1 00:00 subsystem -> ../../../../../../class/pwm
--w------- 1 root root 4.0K Jan 1 00:00 unexport
drwxr-xr-x 2 root root 0 Jan 1 00:00 power
-r--r--r-- 1 root root 4.0K Jan 1 00:00 npwm
--w------- 1 root root 4.0K Jan 1 00:00 export
lrwxrwxrwx 1 root root 0 Jan 1 00:00 device -> ../../../48302100.ecap

Hi,

Yes, this is correct.

Now you can continue using he pwm0/1 as described in the user's guide: processors.wiki.ti.com/.../Linux_Core_PWM_User's_Guide

Best Regards,
Yordan