Re: [PATCH -next 2/2] leds: add /sys/class/leds/<led>/current-trigger

[Dan Murphy]

Jacek

On 10/2/19 12:46 PM, Jacek Anaszewski wrote:
> Dan,
>
> On 10/2/19 5:47 PM, Dan Murphy wrote:
> > Akinobu
> >
> > On 10/2/19 10:13 AM, Akinobu Mita wrote:
> > > Reading /sys/class/leds/<led>/trigger returns all available LED triggers.
> > > However, this violates the "one value per file" rule of sysfs.
> > >
> > > This provides /sys/class/leds/<led>/current-trigger which is almost
> > > identical to /sys/class/leds/<led>/trigger. The only difference is that
> > > 'current-trigger' only shows the current trigger name.
> > >
> > > This new file follows the "one value per file" rule of sysfs.
> > > We can find all available LED triggers by listing the
> > > /sys/devices/virtual/led-trigger/ directory.
> > >
> > > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> > > Cc: Jacek Anaszewski <jacek.anaszewski@xxxxxxxxx>
> > > Cc: Pavel Machek <pavel@xxxxxx>
> > > Cc: Dan Murphy <dmurphy@xxxxxx>
> > > Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
> > > ---
> > >  Â Documentation/ABI/testing/sysfs-class-led | 13 +++++++++++
> > >  Â drivers/leds/led-class.cÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ | 10 ++++++++
> > >  Â drivers/leds/led-triggers.cÂÂÂÂÂÂÂÂÂÂÂÂÂÂ | 38
> > > +++++++++++++++++++++++++++----
> > >  Â drivers/leds/leds.hÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ |Â 5 ++++
> > >  Â 4 files changed, 62 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/Documentation/ABI/testing/sysfs-class-led
> > > b/Documentation/ABI/testing/sysfs-class-led
> > > index 5f67f7a..fdfed3f 100644
> > > --- a/Documentation/ABI/testing/sysfs-class-led
> > > +++ b/Documentation/ABI/testing/sysfs-class-led
> > > @@ -61,3 +61,16 @@ Description:
> > >  ÂÂÂÂÂÂÂÂÂ gpio and backlight triggers. In case of the backlight trigger,
> > >  ÂÂÂÂÂÂÂÂÂ it is useful when driving a LED which is intended to indicate
> > >  ÂÂÂÂÂÂÂÂÂ a device in a standby like state.
> > > +
> > > +What:ÂÂÂÂÂÂÂ /sys/class/leds/<led>/current-trigger
> > > +Date:ÂÂÂÂÂÂÂ September 2019
> > > +KernelVersion:ÂÂÂ 5.5
> > > +Contact:ÂÂÂ linux-leds@xxxxxxxxxxxxxxx
> > > +Description:
> > > +ÂÂÂÂÂÂÂ Set the trigger for this LED. A trigger is a kernel based source
> > > +ÂÂÂÂÂÂÂ of LED events.
> > > +ÂÂÂÂÂÂÂ Writing the trigger name to this file will change the current
> > > +ÂÂÂÂÂÂÂ trigger. Trigger specific parameters can appear in
> > > +ÂÂÂÂÂÂÂ /sys/class/leds/<led> once a given trigger is selected. For
> > > +ÂÂÂÂÂÂÂ their documentation see sysfs-class-led-trigger-*.
> > > +ÂÂÂÂÂÂÂ Reading this file will return the current LED trigger name.
> > Why do we need this new file can't we just update the current trigger
> > file implementation?
> We can't change existing ABI. It doesn't matter if it is documented
> or not - it's in place for very long time and you can't guarantee there
> are no users relying on triggers file show format.

So if it has been in place for a very long time why do we need another 
ABI that does sorta the same thing?

This seems to be a bit confusing and extra.

Maybe this ABI should be RO where a user can read the current-trigger as 
a single value per file but writing the trigger still

is done through the old ABI.

Dan


> > I don't see any documentation that states that the read of the trigger
> > file will print a list of known triggers.
> >
> > And writing to the trigger file still works so I would think the _show
> > just needs to be fixed.
> >
> > Besides this patch does not fix the issue in the commit message that the
> > trigger file still violates the one value per file rule.
> >
> > Dan