linux-kernel - Re: [PATCH 2/2] Input: atmel_mxt_ts

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Date:	Fri, 08 Aug 2014 16:52:13 +0200
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Nick Dyer <nick.dyer@...ev.co.uk>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Stephen Warren <swarren@...dia.com>,
	Yufeng Shen <miletus@...omium.org>,
	Benson Leung <bleung@...omium.org>,
	Doug Anderson <dianders@...omium.org>,
	Olof Johansson <olof@...om.net>, linux-input@...r.kernel.org,
	devicetree@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Input: atmel_mxt_ts - Add keycodes array example

Hello Nick,

On 08/07/2014 02:38 PM, Nick Dyer wrote:
>> 
>> Also, the current documentation says that the array limit
>> is four entries but the driver dynamically allocates the
>> keymap array and does not limit the array size.
> 
> There is a physical limit to the number of GPIOs on the device. The number
> 4 is wrong, the protocol does allow for up to 8 GPIOs. But it is a hard limit.
>

Thanks a lot for the explanation, then I guess s/4/8 is enough.

>> 
>> Signed-off-by: Javier Martinez Canillas <javier.martinez@...labora.co.uk>
>> ---
>>  Documentation/devicetree/bindings/input/atmel,maxtouch.txt | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>> 
>> diff --git a/Documentation/devicetree/bindings/input/atmel,maxtouch.txt b/Documentation/devicetree/bindings/input/atmel,maxtouch.txt
>> index baef432..be50476 100644
>> --- a/Documentation/devicetree/bindings/input/atmel,maxtouch.txt
>> +++ b/Documentation/devicetree/bindings/input/atmel,maxtouch.txt
>> @@ -11,7 +11,7 @@ Required properties:
>>  
>>  Optional properties for main touchpad device:
>>  
>> -- linux,gpio-keymap: An array of up to 4 entries indicating the Linux
>> +- linux,gpio-keymap: An array of entries indicating the Linux
>>      keycode generated by each GPIO. Linux keycodes are defined in
>>      <dt-bindings/input/input.h>.
>>  
>> @@ -22,4 +22,10 @@ Example:
>>  		reg = <0x4b>;
>>  		interrupt-parent = <&gpio>;
>>  		interrupts = <TEGRA_GPIO(W, 3) IRQ_TYPE_LEVEL_LOW>;
>> +		linux,gpio-keymap = < BTN_LEFT
>> +				      BTN_TOOL_FINGER
>> +				      BTN_TOOL_DOUBLETAP
>> +				      BTN_TOOL_TRIPLETAP
>> +				      BTN_TOOL_QUADTAP
>> +				      BTN_TOOL_QUINTTAP >;
> 
> I'm afraid you have misunderstood the impact of this change to the way that
> the GPIOs coming in to the touch controller are mapped to key codes. Look

Unfortunately there are no boards in mainline using this "linux,gpio-keymap"
property so I tried to figure out what the expected values were by reading the
driver. So is more than possible that I got them wrong.

By passing all these keycodes the touchpad worked as expected for me and the
driver did the same than the Chrome OS driver that has these keycodes hardcoded
when is_tp is true.

> at the protocol guide for T19.
> 

I don't have access to proper documentation and I wouldn't expect people to have
access to non-public docs in order to use a Device Tree binding.

That's why I wanted to document an example, so using this property could be
easier for others and they shouldn't have to look at the driver in order to
figure it out (and getting it wrong as you said :) )

So it would be great if you could provide an example on how this is supposed to
be used.

> The DOUBLE/TRIPLE/QUAD/QUINTTAP stuff is filled in for us by the input core
> when we use INPUT_MT_POINTER, anyway.
> 

Thanks for the hint, I didn't know that this was the case but I just looked at
input_mt_init_slots() [0] and indeed those are not needed.

Best regards,
Javier

[0]: http://lxr.free-electrons.com/source/drivers/input/input-mt.c#L69
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