Documentation: small fixes for LEDs, hide notes about vibration

Spell "LED" consistently with uppercase.

We do not want people to use LED subsystem for vibrations; there's already support for that in input subsystem. Remove notes about vibrations not to confuse people.

Signed-off-by Pavel Machek <[email protected]>

Documentation/leds/ledtrig-transient.txt +1 -1

index 3bd38b4..f412603 100644
@@ -1,7 +1,7 @@
 LED Transient Trigger
 =====================
 
-The leds timer trigger does not currently have an interface to activate
+The LED timer trigger does not currently have an interface to activate
 a one shot timer. The current support allows for setting two timers, one for
 specifying how long a state to be on, and the second for how long the state
 to be off. The delay_on value specifies the time period an LED should stay

Documentation/leds/ledtrig-transient.txt +6 -6

 Transient trigger addresses the need for one shot timer activation. The
-transient trigger can be enabled and disabled just like the other leds
+transient trigger can be enabled and disabled just like the other LED
 triggers.
 
-When an led class device driver registers itself, it can specify all leds
+When an LED class device driver registers itself, it can specify all LED
 triggers it supports and a default trigger. During registration, activation
 routine for the default trigger gets called. During registration of an led
 class device, the LED state does not change.

@@ -42,12 +36,12 @@ that are active at the time driver gets suspended, continue to run, without
 being able to actually change the LED state. Once driver is resumed, triggers
 start functioning again.
 
-LED state changes are controlled using brightness which is a common led
+LED state changes are controlled using brightness which is a common LED
 class device property. When brightness is set to 0 from user space via
 echo 0 > brightness, it will result in deactivating the current trigger.
 
 Transient trigger uses standard register and unregister interfaces. During
-trigger registration, for each led class device that specifies this trigger
+trigger registration, for each LED class device that specifies this trigger
 as its default trigger, trigger activation routine will get called. During
 registration, the LED state does not change, unless there is another trigger
 active, in which case LED state changes to LED_OFF.

@@ -56,12 +50,12 @@ During trigger unregistration, LED state gets changed to LED_OFF.
 
 Transient trigger activation routine doesn't change the LED state. It
 creates its properties and does its initialization. Transient trigger
-deactivation routine, will cancel any timer that is active before it cleans
+deactivation routine will cancel any timer that is active before it cleans
 up and removes the properties it created. It will restore the LED state to
 non-transient state. When driver gets suspended, irrespective of the transient
 state, the LED state changes to LED_OFF.
 
-Transient trigger can be enabled and disabled from user space on led class
+Transient trigger can be enabled and disabled from user space on LED class
 devices, that support this trigger as shown below:
 
 echo transient > trigger

Documentation/leds/ledtrig-transient.txt set a timer to hold a state, however when user space application crashes or · line 23

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Documentation/leds/ledtrig-transient.txt +0 -5

-As a specific example of this use-case, let's look at vibrate feature on
-phones. Vibrate function on phones is implemented using PWM pins on SoC or
-PMIC. There is a need to activate one shot timer to control the vibrate
-feature, to prevent user space crashes leaving the phone in vibrate mode
-permanently causing the battery to drain.

I'm not sure if it is a good idea to remove this description. Users will still be able to use transient trigger this way. It has been around for five years already and there are users which employ it in this particular way [0].

Apart from that it's the only documented kernel API for vibrate devices AFAICT.

Hi!

Quoted 10 lines

Documentation/leds/ledtrig-transient.txt set a timer to hold a state, however when user space application crashes or · line 23

Quoted 5 lines

Documentation/leds/ledtrig-transient.txt +0 -5

-As a specific example of this use-case, let's look at vibrate feature on
-phones. Vibrate function on phones is implemented using PWM pins on SoC or
-PMIC. There is a need to activate one shot timer to control the vibrate
-feature, to prevent user space crashes leaving the phone in vibrate mode
-permanently causing the battery to drain.

I'm not sure if it is a good idea to remove this description. Users will still be able to use transient trigger this way. It has been around for five years already and there are users which employ it in this particular way [0].

I am. Yes, people were doing that, but no, vibration motor is not a LED. PWM behaviour is different, for example, motor is likely to stop at low PWM values. We do not want people to do that.

Quoted 2 lines

Apart from that it's the only documented kernel API for vibrate devices AFAICT.

Input subsystem has force-feedback protocol, which is very often just vibrations. Documentation/input/ff.rst . Nokia N900 phone actually uses that API.

Hi!

Quoted 10 lines

Documentation/leds/ledtrig-transient.txt set a timer to hold a state, however when user space application crashes or · line 23

Quoted 5 lines

Documentation/leds/ledtrig-transient.txt +0 -5

-As a specific example of this use-case, let's look at vibrate feature on
-phones. Vibrate function on phones is implemented using PWM pins on SoC or
-PMIC. There is a need to activate one shot timer to control the vibrate
-feature, to prevent user space crashes leaving the phone in vibrate mode
-permanently causing the battery to drain.

I'm not sure if it is a good idea to remove this description. Users will still be able to use transient trigger this way. It has been around for five years already and there are users which employ it in this particular way [0].

I am. Yes, people were doing that, but no, vibration motor is not a LED. PWM behaviour is different, for example, motor is likely to stop at low PWM values. We do not want people to do that.

Quoted 2 lines

Apart from that it's the only documented kernel API for vibrate devices AFAICT.

Input subsystem has force-feedback protocol, which is very often just vibrations. Documentation/input/ff.rst . Nokia N900 phone actually uses that API.

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Documentation/leds/ledtrig-transient.txt set a timer to hold a state, however when user space application crashes or · line 23

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Documentation/leds/ledtrig-transient.txt +0 -5

-As a specific example of this use-case, let's look at vibrate feature on
-phones. Vibrate function on phones is implemented using PWM pins on SoC or
-PMIC. There is a need to activate one shot timer to control the vibrate
-feature, to prevent user space crashes leaving the phone in vibrate mode
-permanently causing the battery to drain.

I'm not sure if it is a good idea to remove this description. Users will still be able to use transient trigger this way. It has been around for five years already and there are users which employ it in this particular way [0].

I am. Yes, people were doing that, but no, vibration motor is not a LED. PWM behaviour is different, for example, motor is likely to stop at low PWM values. We do not want people to do that.

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Apart from that it's the only documented kernel API for vibrate devices AFAICT.

Input subsystem has force-feedback protocol, which is very often just vibrations. Documentation/input/ff.rst . Nokia N900 phone actually uses that API.

N900 as shipped by Nokia used an ad hoc sysfs interface. Because that sucked, I advocated using the force feedback API for N950 and N9. Because what is vibration but force feedback? It's a much more versatile API for vibration than a simple trigger. You get to upload effects and have the kernel play them for you, also stopping them in a timely manner regardless of the userspace dying and whatnot. I didn't double check now, but IIRC you could also link the input to force feedback, e.g. for touch vibrations.

Hi,

Quoted 12 lines · Pavel Machek

Hi!

Quoted 10 lines

Documentation/leds/ledtrig-transient.txt set a timer to hold a state, however when user space application crashes or · line 23

Quoted 5 lines

Documentation/leds/ledtrig-transient.txt +0 -5

-As a specific example of this use-case, let's look at vibrate feature on
-phones. Vibrate function on phones is implemented using PWM pins on SoC or
-PMIC. There is a need to activate one shot timer to control the vibrate
-feature, to prevent user space crashes leaving the phone in vibrate mode
-permanently causing the battery to drain.

I'm not sure if it is a good idea to remove this description. Users will still be able to use transient trigger this way. It has been around for five years already and there are users which employ it in this particular way [0].

Quoted 3 lines

I am. Yes, people were doing that, but no, vibration motor is not a LED. PWM behaviour is different, for example, motor is likely to stop at low PWM values. We do not want people to do that.

Could you elaborate on how it can be harmful?

I really don't see any merit in removing this from documentation.

You can convince me by collecting some acks from involved people. I'd like to especially see Rob's opinion. Adding Rob to this thread.

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Apart from that it's the only documented kernel API for vibrate devices AFAICT.

Input subsystem has force-feedback protocol, which is very often just vibrations. Documentation/input/ff.rst . Nokia N900 phone actually uses that API.

Word "vibration" doesn't appear there, so what this patch does is remove explicit advertisement of kernel support for vibrate devices without redirecting people to the replacement.

Quoted 15 lines · Jacek Anaszewski

Hi,

Quoted 12 lines · Pavel Machek

Hi!

Quoted 10 lines

Documentation/leds/ledtrig-transient.txt set a timer to hold a state, however when user space application crashes or · line 23

Quoted 5 lines

Documentation/leds/ledtrig-transient.txt +0 -5

-As a specific example of this use-case, let's look at vibrate feature on
-phones. Vibrate function on phones is implemented using PWM pins on SoC or
-PMIC. There is a need to activate one shot timer to control the vibrate
-feature, to prevent user space crashes leaving the phone in vibrate mode
-permanently causing the battery to drain.

I'm not sure if it is a good idea to remove this description. Users will still be able to use transient trigger this way. It has been around for five years already and there are users which employ it in this particular way [0].

Actually, I checked, and no ARM mainline board does that.

Quoted 5 lines

Quoted 3 lines

I am. Yes, people were doing that, but no, vibration motor is not a LED. PWM behaviour is different, for example, motor is likely to stop at low PWM values. We do not want people to do that.

Could you elaborate on how it can be harmful?

Well, you can safely route low current to the LEDs. What will it to do vibration motor, if you leave it on forever? Can the motor safely be run forever on high current? Not sure.

Quoted 1 line

I really don't see any merit in removing this from documentation.

There's right API to use for vibrations, and that's force-feedback support in input/. Not here.

Quoted 2 lines

You can convince me by collecting some acks from involved people. I'd like to especially see Rob's opinion. Adding Rob to this thread.

Rob is device tree maintainer. This has little to do with device tree.

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Apart from that it's the only documented kernel API for vibrate devices AFAICT.

Input subsystem has force-feedback protocol, which is very often just vibrations. Documentation/input/ff.rst . Nokia N900 phone actually uses that API.

Quoted 3 lines

Word "vibration" doesn't appear there, so what this patch does is remove explicit advertisement of kernel support for vibrate devices without redirecting people to the replacement.

Well... this is LED documentation. If there's other documentation missing somewhere else... we can fix it :-).

Hi,

Quoted 17 lines · Pavel Machek

Quoted 15 lines · Jacek Anaszewski

Hi,

Quoted 12 lines · Pavel Machek

Hi!

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Documentation/leds/ledtrig-transient.txt set a timer to hold a state, however when user space application crashes or · line 23

Quoted 5 lines

Documentation/leds/ledtrig-transient.txt +0 -5

-As a specific example of this use-case, let's look at vibrate feature on
-phones. Vibrate function on phones is implemented using PWM pins on SoC or
-PMIC. There is a need to activate one shot timer to control the vibrate
-feature, to prevent user space crashes leaving the phone in vibrate mode
-permanently causing the battery to drain.

I'm not sure if it is a good idea to remove this description. Users will still be able to use transient trigger this way. It has been around for five years already and there are users which employ it in this particular way [0].

Quoted 1 line

Actually, I checked, and no ARM mainline board does that.

There might be user space clients like the Android one [0].

Quoted 9 lines

Quoted 5 lines

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I am. Yes, people were doing that, but no, vibration motor is not a LED. PWM behaviour is different, for example, motor is likely to stop at low PWM values. We do not want people to do that.

Could you elaborate on how it can be harmful?

Well, you can safely route low current to the LEDs. What will it to do vibration motor, if you leave it on forever? Can the motor safely be run forever on high current? Not sure.

It's actually one of the main advantages of the "transient" trigger - you have to re-activate it after the end of each transition cycle,

If you execute the following sequence of commands, then you're getting 1s blink every 3s as long as the while loop is iterating. If you break the loop the LED output state will be always brought down after the duration period, No risk that output will be left in the high state unless transient state was deliberately set to 0.

# echo 1 > state
# echo 1000 > duration
# while [ 1 ] ;do echo 1 > activate ; sleep 3; done

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I really don't see any merit in removing this from documentation.

There's right API to use for vibrations, and that's force-feedback support in input/. Not here.

Is is as easy to use as this one? It seems that it requires an application to call ioctl's.

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Quoted 2 lines

You can convince me by collecting some acks from involved people. I'd like to especially see Rob's opinion. Adding Rob to this thread.

Rob is device tree maintainer. This has little to do with device tree.

I added him because his is the author of the Android patch [0], that mentions using transient trigger for the LED device named "vibrator".

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Apart from that it's the only documented kernel API for vibrate devices AFAICT.

Input subsystem has force-feedback protocol, which is very often just vibrations. Documentation/input/ff.rst . Nokia N900 phone actually uses that API.

Word "vibration" doesn't appear there, so what this patch does is remove explicit advertisement of kernel support for vibrate devices without redirecting people to the replacement.

Quoted 2 lines

Well... this is LED documentation. If there's other documentation missing somewhere else... we can fix it :-).

We can fix it, but not necessarily remove the valuable information from this one :-)