Linux/AM5728: PWM on Timer15

Hi Krunal, thanks for the response. Once I enabled timer15, I'm making some progress. Here is my full change:

@@ -89,6 +89,11 @@
gpio = <&gpio7 3>;
};

+ beeper: pwm_beeper {
+ status = "okay";
+ compatible = "pwm-beeper";
+ pwms = <&timer15 0 5000 1>;
+ };


+&timer15 {
+ status = "okay";
+ pinctrl-names = "default";
+ pinctrl-0 = <&timer15_pins>;
+};
+
+


&dra7_pmx_core {
+ timer15_pins: timer15_pins_default {
+ pinctrl-single,pins = <
+ DRA7XX_CORE_IOPAD(0x36A0, PIN_OUTPUT | MUX_MODE10)
+ >;
+ };

Unfortunately, it's not working 100% yet:

root@dev:~# dmesg | grep -i pwm
[    2.248063] palmas 0-0058: Muxing GPIO 2b, PWM 0, LED 0
[    7.269426] lp8863 0-003c: BL Mode Register Read (0x0: PWM 0x2: DISPLAY_BRT): 0x302
[    7.444450] OF: /pwm_beeper: could not get #pwm-cells for /ocp/timer@4882c000
[    7.463389] of_pwm_get(): can't parse "pwms" property
[    7.480388] pwm-beeper pwm_beeper: Failed to request PWM device: -22
[    7.501369] pwm-beeper: probe of pwm_beeper failed with error -22
root@dev:~# dmesg | grep -i timer
[    0.000000] OMAP clockevent source: timer1 at 32786 Hz
[    0.000000] arch_timer: cp15 timer(s) running at 6.14MHz (phys).
[    0.000017] Switching to timer-based delay loop, resolution 162ns
[    0.000885] Calibrating delay loop (skipped), value calculated using timer frequency.. 12.29 BogoMIPS (lpj=61475)
[    7.181794] omap_wdt: OMAP Watchdog Timer Rev 0x01: initial timeout 60 sec
[    7.444450] OF: /pwm_beeper: could not get #pwm-cells for /ocp/timer@4882c000

Pointers will be appreciated, especially I'd like some check on the pwms property I bold faced above.

Ok thanks that did do the trick. I can hear the beep now:

root:~# cat /sys/kernel/debug/pwm
platform/dmtimer-pwm@15, 1 PWM device
 pwm-0   (pwm_beeper          ): requested period: 250000 ns duty: 0 ns polarity: normal

root:~# cd /sys/class/pwm
root:/sys/class/pwm# cd pwmchip0
root:/sys/class/pwm/pwmchip0# echo 0 > export
root@solix:/sys/class/pwm/pwmchip0# cd pwm0
root@solix:/sys/class/pwm/pwmchip0/pwm0# echo 190000 > duty_cycle
root@solix:/sys/class/pwm/pwmchip0/pwm0# cat /sys/kernel/debug/pwm
platform/dmtimer-pwm@15, 1 PWM device
 pwm-0   (sysfs               ): requested period: 250000 ns duty: 190000 ns polarity: normal

root@solix:/sys/class/pwm/pwmchip0/pwm0# echo 1 > enable

All this is good. Thanks!

I'm working with Adam, we made the following changes in the correct sections in the dts file:

+       pwm15: dmtimer-pwm@15 {
+               compatible = "ti,omap-dmtimer-pwm";
+               ti,timers = <&timer15>;
+               #pwm-cells = <3>;
+       };
+
+       beeper: pwm_beeper {
+               status = "okay";
+               compatible = "pwm-beeper";
+               pwms = <&pwm15 0 250000 0>;
+       };

+&timer15 {
+       status = "okay";
+       ti,timer-pwm;
+       pinctrl-names = "default";
+       pinctrl-0 = <&timer15_pins>;
+};
+

+       timer15_pins: timer15_pins_default {
+               pinctrl-single,pins = <
+                       DRA7XX_CORE_IOPAD(0x369C, PIN_OUTPUT | MUX_MODE10)
+               >;
+       };
+

We also used menuconfig to enable the following options:

CONFIG_INPUT_PWM_BEEPER=m

CONFIG_PWM_OMAP_DMTIMER=m

We tried both as part of the kernel (=y) but we couldn't communicate with the device. Is that expected or can it be configured as part of the kernel? Is there a better way to enable & access the PWM functionality to drive a beeper connected to B26 / output from timer15?

ScottS said:

We tried both as part of the kernel (=y) but we couldn't communicate with the device.

Can you elaborate?  What are you doing to communicate with it, and what is the result?  (Any error messages, etc.)

Hi Brad,

I used "menuconfig" to change the CONFIG_INPUT_PWM_BEEPER and CONFIG_PWM_OMAP_DMTIMER values. Only if both are modules / 'm' can we communicate with the device to generate a tone.

CONFIG_INPUT_PWM_BEEPER=y
CONFIG_PWM_OMAP_DMTIMER=y
lsmod shows neither pwm_beeper now pwm_omap_dmtimer
/sys/class/pwm/pwmchip0 doesn't exist
# dmesg | grep beep shows nothing
# dmesg | grep -i dmtimer
omap-dmtimer-pwm dmtimer-pwm@15: dmtimer pdata structure NULL
omap-dmtimer-pwm: probe of dmtimer-pwm@15 failed with error -22



CONFIG_INPUT_PWM_BEEPER=m
CONFIG_PWM_OMAP_DMTIMER=y
lsmod shows pwm_beeper
/sys/class/pwm/pwmchip0 doesn't exist
# dmesg | grep beep shows nothing
# dmesg | grep -i dmtimer
omap-dmtimer-pwm dmtimer-pwm@15: dmtimer pdata structure NULL
omap-dmtimer-pwm: probe of dmtimer-pwm@15 failed with error -22




CONFIG_INPUT_PWM_BEEPER=y
CONFIG_PWM_OMAP_DMTIMER=m
lsmod shows pwm_omap_dmtimer
/sys/class/pwm/pwmchip0 exists
/sys/class/pwm/pwmchip0/pwm0 doesn't exist

# echo 0 > /sys/class/pwm/pwmchip0/export
-sh: echo: write error: Device or resource busy

# cat /sys/class/pwm/pwmchip0/npwm
1

# rmmod pwm_omap_dmtimer
rmmod: ERROR: Module pwm_omap_dmtimer is in use

# cat /sys/kernel/debug/pwm
platform/dmtimer-pwm@15, 1 PWM device
 pwm-0   (pwm_beeper          ): requested period: 250000 ns duty: 0 ns polarity: normal




CONFIG_INPUT_PWM_BEEPER=m
CONFIG_PWM_OMAP_DMTIMER=m
lsmod shows both pwm_beeper and pwm_omap_dmtimer
/sys/class/pwm/pwmchip0 exists
/sys/class/pwm/pwmchip0/pwm0 doesn't exist
have to "rmmod pwm_beeper" before we use "echo 0 > /sys/class/pwm/pwmchip0/export", then "/sys/class/pwm/pwmchip0/pwm0" exists
can now write to "period", "duty_cycle", and "enable" as needed

# cat /sys/kernel/debug/pwm
platform/dmtimer-pwm@15, 1 PWM device
 pwm-0   (pwm_beeper          ): requested period: 250000 ns duty: 0 ns polarity: normal

# dmesg | grep beep
[    6.759203] pwm-beeper pwm_beeper: pwm_beeper supply amp not found, using dummy regulator
[    6.780730] pwm-beeper pwm_beeper: failed to parse 'beeper-hz' property, using default: 1000Hz
[    6.781021] input: pwm-beeper as /devices/platform/pwm_beeper/input/input0

# dmesg | grep -i dmtimer
[    6.618756] omap-dmtimer-pwm dmtimer-pwm@15: requested duty cycle: 0 ns, period: 250000 ns
[    6.618767] omap-dmtimer-pwm dmtimer-pwm@15: clk rate: 32786Hz
[    6.716315] omap-dmtimer-pwm dmtimer-pwm@15: duty cycle 0 ns is too short for clock rate 32786 Hz
[    6.716323] omap-dmtimer-pwm dmtimer-pwm@15: using minimum of 1 clock cycle
[    6.716329] omap-dmtimer-pwm dmtimer-pwm@15: effective duty cycle: 30501 ns, period: 244007 ns
[    6.717808] omap-dmtimer-pwm dmtimer-pwm@15: load value: 0xfffffff8 (-8), match value: 0xfffffff8 (-8)

Thanks,

Scott

Did you use make modules_install to properly install these modules into the file system?  Did they ever get loaded, either automatically or through insmod/depmod?

I have the same question. When the timer-pwm is configured as a part of kernel, the timer-pwm will not work properly. It's like there are some boot sequence requirements.

Hi Brad,

We tried everything we could think of but the only combination that works is configure both as loadable modules. It doesn't work if either are part of the kernel.

Unfortunately, we had to stop using the drivers and write directly to the registers for timer 15 due to a 80ms +- 20ms delay when changing frequency. We are playing a sequence of tones and a those delays between notes is very noticeable.

Scott

Hi Scott,

I was able to replicate your problem and I was only able to generate a PWM with CONFIG_PWM_OMAP_DMTIMER=m. I believe this may be a bug with the driver and I am investigating more into this problem. 

In the meantime, if you plan on using the driver, please build it as a module.

Regards,
Krunal

Hi Krunal,

Thank you for researching the module vs kernel issue and finding a resolution.

Unfortunately, we had to stop using the drivers and write directly to the registers for timer 15. Using the pwm driver, there is a 80ms +- 20ms delay when changing frequency. We are playing a sequence of tones and a those delays between notes is very noticeable.

Scott

Hi Scott,

Thank you for the update. I will be closing the ticket and if you have more questions, please feel free to open the ticket in the future.

Regards,
Krunal