On 11.10.2016 15:39, Rob Herring wrote:
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.
Ok
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.
I see. I will resend and change the description to make clear, that the
volume-levels property is meant to specify linear volume levels.
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.
Ok, I will drop this.
Rob
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