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Message-ID: <5743E206.2050602@ti.com> Date: Tue, 24 May 2016 10:39:26 +0530 From: Vignesh R <vigneshr@...com> To: Uwe Kleine-König <u.kleine-koenig@...gutronix.de> CC: Dmitry Torokhov <dmitry.torokhov@...il.com>, Rob Herring <robh+dt@...nel.org>, Tony Lindgren <tony@...mide.com>, Jonathan Corbet <corbet@....net>, Johan Hovold <johan@...nel.org>, Sylvain Rochet <sylvain.rochet@...secur.com>, Masanari Iida <standby24x7@...il.com>, Ezequiel Garcia <ezequiel@...guardiasur.com.ar>, S Twiss <stwiss.opensource@...semi.com>, Krzysztof Kozlowski <k.kozlowski@...sung.com>, Moritz Fischer <moritz.fischer@...us.com>, Arnd Bergmann <arnd@...db.de>, Geert Uytterhoeven <geert@...ux-m68k.org>, Timo Teras <timo.teras@....fi>, Clifton Barnes <clifton.a.barnes@...il.com>, "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: [RFC PATCH 1/2] Input: rotary-encoder- Add support for absolute encoder Hi, On 05/23/2016 06:48 PM, Uwe Kleine-König wrote: > 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? No, I am not against the use of IRQs. In fact, my patches add support for both IRQ based(default) and polling based operation(optional). If rotary-encoder does not have interrupt capable gpio lines connected to it (like am335x-ice) then one can make use of the polling mode support. > >> 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. > More complexity is just a overhead. Since, encoder can be turned at a rate faster than handling of IRQs (rotary_encoder_quarter_period_irq() is threaded IRQ hence, priority is not close to real time), some states can be missed. rotary_encoder_quarter_period_irq() is not robust in this case, reading gpios directly is more suitable option. I see similar views expressed in previously[1] [1]http://lists.infradead.org/pipermail/linux-arm-kernel/2015-December/391196.html -- Regards Vignesh
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