Hello, On Mon, May 23, 2016 at 04:48:40PM +0530, R, Vignesh wrote: > On 5/22/2016 3:56 PM, Uwe Kleine-König wrote: > > Hello, > > > > On Thu, May 19, 2016 at 02:34:00PM +0530, Vignesh R wrote: > >> There are rotary-encoders where GPIO lines reflect the actual position > >> of the rotary encoder dial. For example, if dial points to 9, then four > >> GPIO lines connected to the rotary encoder will read HLLH(1001b = 9). > >> Add support for such rotary-encoder. > >> The driver relies on rotary-encoder,absolute-encoder DT property to > >> detect such encoders. > >> Since, GPIO IRQs are not necessary to work with > >> such encoders, optional polling mode support is added using > > > > I don't understand this. It's necessary in the same way as with the > > already supported devices. I.e. you want to trigger an irq when the > > encoder is moved and then check for it's position in the handler. > > > > Unlike already supported device, there is no need to count steps or > determine the direction of rotation. Hence, IRQ is not a requirement, > periodically polling the gpio lines is more than sufficient. With > absolute encoder, you are able to determine the current position at any > time just by looking at the gpio inputs. The timing might not be that critical, but there is no reason to operate this device without irqs, is there? > Suppose we poll device at t=0ms and see gpio values are LLLH(1), if we > again poll device at t=500ms(which is what input_poll_dev helps to do) > and see that gpio values is LLHH(3), then we know that rotary encoder > has changed to 3. This can be done w/o IRQ for absolute encoders. > > >> diff --git a/Documentation/devicetree/bindings/input/rotary-encoder.txt b/Documentation/devicetree/bindings/input/rotary-encoder.txt > >> index 6c9f0c8a846c..9c928dbd1500 100644 > >> --- a/Documentation/devicetree/bindings/input/rotary-encoder.txt > >> +++ b/Documentation/devicetree/bindings/input/rotary-encoder.txt > >> @@ -12,6 +12,10 @@ Optional properties: > >> - rotary-encoder,relative-axis: register a relative axis rather than an > >> absolute one. Relative axis will only generate +1/-1 events on the input > >> device, hence no steps need to be passed. > >> +- rotary-encoder,absolute-encoder: support encoders where GPIO lines > >> + reflect the actual position of the rotary encoder dial. For example, > >> + if dial points to 9, then four GPIO lines read HLLH(1001b = 9). > >> + In this case, rotary-encoder,steps-per-period needed not be defined. > > > > IMHO this is wrong, I'd formalize this device as: > > > > { > > compatible = "rotary-encoder"; > > gpios = <&gpio 19 1>, <&gpio 20 0>, <...>, <...>; > > rotary-encoder,encoding = "binary"; > > rotary-encoder,steps = <16>; > > rotary-encoder,steps-per-period = <16>; > > The above bindings essential means quarter_period device. I would not > like to bother with all the logic in rotary_encoder_quarter_period_irq() > when we can know encoder->pos by directly reading state of gpio lines. OK, we have code that is more complex than it needs to be for your device. But your device is a special case of the supported devices, so I'd say don't bother that there is more logic in the driver than you need and be lucky. > > rotary-encoder,rollover; > > } > > > > and support this with a v4 of > > > > http://thread.gmane.org/gmane.linux.kernel.input/48892 > > > > > > IMHO, there needs to be separate IRQ handler for absolute encoders so > that the driver logic is greatly simplified. As above, the added complexity can handle your case just fine. So just use it. One thing I see to improve is to make use of the additional GPIOs, but this is orthogonal to the different encoding and the question if polling is enough here. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html