| Message ID | 20150308205732.GA385@amd (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Pavel, On Sun, Mar 8, 2015 at 9:57 PM, Pavel Machek <pavel@ucw.cz> wrote: > Ok, so I played with RGB LED a bit, and we have quite a gap in > documentation: what 50% brightness means is non-trivial and very > important in case we want to do smooth blinking and color transitions. > > Signed-off-by: Pavel Machek <pavel@ucw.cz> > > diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led > index 3646ec8..649d7a6 100644 > --- a/Documentation/ABI/testing/sysfs-class-led > +++ b/Documentation/ABI/testing/sysfs-class-led > @@ -8,6 +8,11 @@ Description: > non-zero brightness settings. The value is between 0 and > /sys/class/leds/<led>/max_brightness. > > + If LED supports continuous brightness settings, 50% brightness > + should correspond to 50% brightness perceived by human, in a similar > + manner pixel brightness on monitor does (not 50% PWM). How many drivers do it right? How many don't? For those that don't, perhaps we handle the conversion between perceived and pwm in the core, e.g. by adding a new flag to led_classdev.flags to indicate the need for conversion? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon 2015-03-09 09:08:37, Geert Uytterhoeven wrote: > Hi Pavel, > > On Sun, Mar 8, 2015 at 9:57 PM, Pavel Machek <pavel@ucw.cz> wrote: > > Ok, so I played with RGB LED a bit, and we have quite a gap in > > documentation: what 50% brightness means is non-trivial and very > > important in case we want to do smooth blinking and color transitions. > > > > Signed-off-by: Pavel Machek <pavel@ucw.cz> > > > > diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led > > index 3646ec8..649d7a6 100644 > > --- a/Documentation/ABI/testing/sysfs-class-led > > +++ b/Documentation/ABI/testing/sysfs-class-led > > @@ -8,6 +8,11 @@ Description: > > non-zero brightness settings. The value is between 0 and > > /sys/class/leds/<led>/max_brightness. > > > > + If LED supports continuous brightness settings, 50% brightness > > + should correspond to 50% brightness perceived by human, in a similar > > + manner pixel brightness on monitor does (not 50% PWM). > > How many drivers do it right? How many don't? Not sure. leds-lp5523.c gets is wrong. Easy test is to attempt to set "electric indigo" color (http://en.wikipedia.org/wiki/Indigo#Violet-blue) and see what comes out. > For those that don't, perhaps we handle the conversion between perceived and > pwm in the core, e.g. by adding a new flag to led_classdev.flags to indicate > the need for conversion? There is not that many drivers that support smooth power adjustments. But yes, we can probably conversion in the core for trivial case. Unfortunately, we only have 8-bits of precision to work with... Pavel
Geert Uytterhoeven <geert@linux-m68k.org> writes: > Hi Pavel, > > On Sun, Mar 8, 2015 at 9:57 PM, Pavel Machek <pavel@ucw.cz> wrote: >> Ok, so I played with RGB LED a bit, and we have quite a gap in >> documentation: what 50% brightness means is non-trivial and very >> important in case we want to do smooth blinking and color transitions. >> >> Signed-off-by: Pavel Machek <pavel@ucw.cz> >> >> diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led >> index 3646ec8..649d7a6 100644 >> --- a/Documentation/ABI/testing/sysfs-class-led >> +++ b/Documentation/ABI/testing/sysfs-class-led >> @@ -8,6 +8,11 @@ Description: >> non-zero brightness settings. The value is between 0 and >> /sys/class/leds/<led>/max_brightness. >> >> + If LED supports continuous brightness settings, 50% brightness >> + should correspond to 50% brightness perceived by human, in a similar >> + manner pixel brightness on monitor does (not 50% PWM). > > How many drivers do it right? How many don't? > > For those that don't, perhaps we handle the conversion between perceived and > pwm in the core, e.g. by adding a new flag to led_classdev.flags to indicate > the need for conversion? Some LED controllers do the right thing in hardware, so any adjustment done in the core needs to be optional.
On Mon 2015-03-09 11:50:56, Måns Rullgård wrote: > Geert Uytterhoeven <geert@linux-m68k.org> writes: > > > Hi Pavel, > > > > On Sun, Mar 8, 2015 at 9:57 PM, Pavel Machek <pavel@ucw.cz> wrote: > >> Ok, so I played with RGB LED a bit, and we have quite a gap in > >> documentation: what 50% brightness means is non-trivial and very > >> important in case we want to do smooth blinking and color transitions. > >> > >> Signed-off-by: Pavel Machek <pavel@ucw.cz> > >> > >> diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led > >> index 3646ec8..649d7a6 100644 > >> --- a/Documentation/ABI/testing/sysfs-class-led > >> +++ b/Documentation/ABI/testing/sysfs-class-led > >> @@ -8,6 +8,11 @@ Description: > >> non-zero brightness settings. The value is between 0 and > >> /sys/class/leds/<led>/max_brightness. > >> > >> + If LED supports continuous brightness settings, 50% brightness > >> + should correspond to 50% brightness perceived by human, in a similar > >> + manner pixel brightness on monitor does (not 50% PWM). > > > > How many drivers do it right? How many don't? > > > > For those that don't, perhaps we handle the conversion between perceived and > > pwm in the core, e.g. by adding a new flag to led_classdev.flags to indicate > > the need for conversion? > > Some LED controllers do the right thing in hardware, so any adjustment > done in the core needs to be optional. Do you have example controller that gets it right, btw? Bryan, can you apply the documentation patch so we can start fixing the drivers? Thanks, Pavel
diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led index 3646ec8..649d7a6 100644 --- a/Documentation/ABI/testing/sysfs-class-led +++ b/Documentation/ABI/testing/sysfs-class-led @@ -8,6 +8,11 @@ Description: non-zero brightness settings. The value is between 0 and /sys/class/leds/<led>/max_brightness. + If LED supports continuous brightness settings, 50% brightness + should correspond to 50% brightness perceived by human, in a similar + manner pixel brightness on monitor does (not 50% PWM). + + What: /sys/class/leds/<led>/max_brightness Date: March 2006 KernelVersion: 2.6.17
Ok, so I played with RGB LED a bit, and we have quite a gap in documentation: what 50% brightness means is non-trivial and very important in case we want to do smooth blinking and color transitions. Signed-off-by: Pavel Machek <pavel@ucw.cz>