On Tue, Oct 11, 2016 at 3:17 AM, Schrempf Frieder <frieder.schrempf@xxxxxxxxx> wrote: > On 10.10.2016 17:20, Rob Herring wrote: >> On Fri, Oct 07, 2016 at 09:08:17AM +0000, Schrempf Frieder wrote: >>> This patch adds the documentation for the devicetree bindings to set >>> the volume levels. >>> >>> Signed-off-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxx> >>> --- >>> Changes in v2: >>> - split into 3 separate patches >>> - make volume properties optional >>> >>> .../devicetree/bindings/input/pwm-beeper.txt | 22 ++++++++++++++++++++++ >>> 1 file changed, 22 insertions(+) >>> >>> diff --git a/Documentation/devicetree/bindings/input/pwm-beeper.txt b/Documentation/devicetree/bindings/input/pwm-beeper.txt >>> index be332ae..6d8ba4e 100644 >>> --- a/Documentation/devicetree/bindings/input/pwm-beeper.txt >>> +++ b/Documentation/devicetree/bindings/input/pwm-beeper.txt >>> @@ -5,3 +5,25 @@ Registers a PWM device as beeper. >>> Required properties: >>> - compatible: should be "pwm-beeper" >>> - pwms: phandle to the physical PWM device >>> + >>> +Optional properties: >>> +- volume-levels: Array of distinct volume levels. These need to be in the >>> + range of 0 to 500, while 0 means 0% duty cycle (mute) and 500 means >>> + 50% duty cycle (max volume). >>> + Please note that the actual volume of most beepers is highly >>> + non-linear, which means that low volume levels are probably somewhere >>> + in the range of 1 to 30 (0.1-3% duty cycle). >> >> What does the index correspond to? The linear volume? > > In most cases users probably need linear volume levels (e.g. 0%, 25%, > 50%, 75%, 100%) and in this case the index would indeed correspond to > the linear perceived volume. > > But also non-linear relations are possible (e.g. 0%, 20%, 100%), if the > user needs for example "mute", "low", "high" as volume levels. Exclude off/mute and this is still linear. Also, the user exposed levels could be a subset of the defined h/w levels. That should be independent of DT. > The linearization (defining the corresponding duty cycle for each index) > depends on the beeper and the perception of the user. This has to be a consistent interface across h/w to have a userspace that can work across h/w. For that, you have to define the binding as linear. Of course, it's all measured by perception and not completely accurate which is fine. > For the example array definition below, I tried different duty cycles > and found values of 0.8%, 2%, 4%, 50% to be approximately correspondent > to perceived volume levels of 25%, 50%, 75%, 100% in my case. > >> >>> +- default-volume-level: the default volume level (index into the >>> + array defined by the "volume-levels" property) >>> + >>> +The volume level can be set via sysfs under /sys/class/input/inputX/volume. >>> +The maximum volume level index can be read from /sys/class/input/inputX/max_volume_level. Also, drop this. Not relevant to the binding. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
