From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH resend v2 1/2] Input: touchscreen DT binding - add touchscreen-min-x and -min-y properties References: <20180731111958.20043-1-hdegoede@redhat.com> <20180731111958.20043-2-hdegoede@redhat.com> <20180803003101.GA118981@dtor-ws> <6f1b0575-87e7-3443-9080-5abfd8e6c726@redhat.com> <20181011005243.GC173303@dtor-ws> From: Hans de Goede Message-ID: <4abed8d4-9d23-bf9c-3cca-a5c521062ea1@redhat.com> Date: Thu, 11 Oct 2018 11:09:49 +0200 MIME-Version: 1.0 In-Reply-To: <20181011005243.GC173303@dtor-ws> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit To: Dmitry Torokhov Cc: Benjamin Tissoires , robh@kernel.org, devicetree@vger.kernel.org, linux-input@vger.kernel.org List-ID: Hi, On 11-10-18 02:52, Dmitry Torokhov wrote: > Hi Hans, > > Sorry, now I was being slow as well. No problem. > On Thu, Sep 20, 2018 at 07:31:43PM +0200, Hans de Goede wrote: >> Hi, >> >> I completely missed this mail earlier, sorry. >> >> Thank you Benjamin for pointing this out to me. >> >> On 03-08-18 02:31, Dmitry Torokhov wrote: >>> Hi Hans, >>> >>> On Tue, Jul 31, 2018 at 01:19:57PM +0200, Hans de Goede wrote: >>>> Some touchscreens, depending on the firmware and/or the digitizer report >>>> coordinates which never reach 0 along one or both of their axis. >>>> >>>> This has been seen for example on the Silead touchscreens on a Onda V891w >>>> and a Point of View mobii TAB-P800w(v2.0). >>>> >>>> This commits documents 2 new touchscreen properties for communicating >>>> the minimum reported values to the OS: touchscreen-min-x and -min-y. >>>> >>>> This commit also drop the (in pixels) comment from the documentation >>>> of the touchscreen-size-x and touchscreen-size-y properties. This comment >>>> suggests that there is a relation between the range of reported >>>> coordinates and the display resolution, which is only true for some >>>> devices. The (in pixels) comment is replaced with "(maximum x coordinate >>>> reported + 1)" to mirror the language describing the new touchscreen-min-x >>>> and -min-y properties. >>> >>> I am concerned that people will not read the documentation carefully and >>> will treat it as true size, since it is what in the name. Maybe we >>> should say that it is size of usable area, in device units, and that >>> maximum reported coordinate is "touchscreen-min-x + touchscreen-size-x - >>> 1"? >> >> Not sure what you mean with "true size" but in the implementation >> from this series, the maximum coordinated reported is (touchscreen-size-x - 1) >> not (touchscreen-min-x + touchscreen-size-x - 1) as you suggest. >> >> Basically what this series does is set: >> >> input_absinfo.minimum to the new touchscreen-min-x value (or 0 if not specified) >> input_absinfo.maximum to touchscreen-size-x - 1 as we've always done. >> >> So the usable range / the range mapping from one screen edge to the other is: >> >> touchscreen-min-x - (touchscreen-size-x - 1) >> >> Which matches with the dt bindings doc after this patch, which >> reads after this patch: >> >> - touchscreen-min-x : minimum x coordinate reported (0 if not set) >> - touchscreen-min-y : minimum y coordinate reported (0 if not set) >> - touchscreen-size-x : horizontal resolution of touchscreen >> (maximum x coordinate reported + 1) >> - touchscreen-size-y : vertical resolution of touchscreen >> (maximum y coordinate reported + 1) >> >> I hope this clarifies things and if you want to change anything let >> me know. > > Right, except that my concern is that people do not read documentation, > and therefore will not realize that touchscreen-size-x is not the "true" > what I called it, or what you call usable range, but rather maximum > coordinate (-1). IOW I am concerned that if we have a device with > 640x480 screen for example, and touch controller reporting coordinates > with offset of 20, someone will specify: > > touchscreen-min-x = 20 > touchscreen-size-x = 640 (because that's their screen size) > > and will not notice for some reason and later quirk it in their > software. Ah I see. > So I was asking if we should accommodate this, and actually set up max > on axis as "touchscreen-min-x + touchscreen-size-x - 1". It will still > be compatible with current bindings (having effectively min of 0), but > to me better reflects the name of the parameter - size of the screen. > > Please let me know if this makes any sense to you. I understand what you want now and why you want it. But I'm not sure I agree with you. Some pre-cursor to this patch series actually had something like touchscreen-offset-x (or some-such I don't remember) which actually subtracted the specified value from the coordinates reported to userspace (clamping to 0). In that setup I think setting: touchscreen-size-x = (maximum x coordinate reported + 1) - (minimum x coordinate reported. Makes sense, but since now we are not doing that and just copying the values over to input_absinfo.minimum/maximum I think a 1:1 mapping (with the - 1 adjustment for size) makes more sense. The way I'm currently using this is with touchscreens where we cannot read this info from the hardware, so I repeatedly move my finger over each edge noting down the min / max value for e.g. the left/right edge and then directly putting these into the properties. IMHO not having to do some math here to calculate the right value for touchscreen-size-x shows that treating touchscreen-size-x as (touchscreen-max-x + 1) is the right thing to do. I'm actually worried that if we follow your suggestion people will indeed not read the docs and thus not do the math. I think they will just copy over the min / max readings and we and up with an input_absinfo.maximum value which is input_absinfo.minimum units too big. Regards, Hans