linux-kernel - Re: [PATCH 2/2] Documentation: DT: bindings: input: Add documentation for cyttsp5

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Date:   Fri, 9 Jun 2017 13:32:38 +0200
From:   Mylene Josserand <mylene.josserand@...e-electrons.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh@...nel.org>
Cc:     fery@...ress.com, mark.rutland@....com,
        linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        devicetree@...r.kernel.org, thomas.petazzoni@...e-electrons.com,
        maxime.ripard@...e-electrons.com
Subject: Re: [PATCH 2/2] Documentation: DT: bindings: input: Add documentation
 for cyttsp5

Hi Dmitry,

Thank you for the review!

On 07/06/2017 22:40, Dmitry Torokhov wrote:
> On Wed, Jun 07, 2017 at 03:26:03PM -0500, Rob Herring wrote:
>> On Mon, May 29, 2017 at 04:45:38PM +0200, Mylène Josserand wrote:
>>> Add the Cypress TrueTouch Generation 5 touchscreen device tree bindings
>>> documentation. It can use I2C or SPI bus.
>>> This touchscreen can handle some defined zone that are designed and
>>> sent as button. To be able to customize the keycode sent, the
>>> "linux,code" property in a "button" sub-node can be used.
>>
>> "documentation" twice in the subject makes for a long subject.
>> The preferred subject prefix is "dt-bindings: input: ..."
>>
>>>
>>> Signed-off-by: Mylène Josserand <mylene.josserand@...e-electrons.com>
>>> ---
>>>  .../bindings/input/touchscreen/cyttsp5.txt         | 55 ++++++++++++++++++++++
>>
>> cypress,cyttsp5.txt matching the compatible is preferred.
>>
>>>  1 file changed, 55 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/input/touchscreen/cyttsp5.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/input/touchscreen/cyttsp5.txt b/Documentation/devicetree/bindings/input/touchscreen/cyttsp5.txt
>>> new file mode 100644
>>> index 000000000000..713a377b5039
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/input/touchscreen/cyttsp5.txt
>>> @@ -0,0 +1,55 @@
>>> +* Cypress cyttsp touchscreen controller, generation 5
>>> +
>>> +Required properties:
>>> + - compatible		: must be "cypress,cyttsp5"
>>> + - reg			: Device I2C address or SPI chip select number
>>> + - interrupt-parent	: the phandle for the gpio controller
>>> +			  (see interrupt binding[0]).
>>> + - interrupts		: (gpio) interrupt to which the chip is connected
>>> +			  (see interrupt binding[0]).
>>> +
>>> +Optional properties (many of them coming from touchscreen binding[1]):
>>> + - reset-gpios		: the reset gpio the chip is connected to
>>> +			  (see GPIO binding[2] for more details).
>>> + - touchscreen-size-x	: horizontal resolution of touchscreen (in pixels)
>>
>> Just "see ./touchscreen.txt" is enough description.
>>
>>> + - touchscreen-size-y	: vertical resolution of touchscreen (in pixels)
>>> + - touchscreen-fuzz-x	: horizontal noise value of the absolute input device
>>> +			  (in pixels)
>>> + - touchscreen-fuzz-y	: vertical noise value of the absolute input device
>>> +			  (in pixels)
>>> +
>>> +This touchscreen can handle some buttons that are touchscreen's defined zones.
>>> +Each button's event can be customized using a sub-node properties:
>>> +	- linux,code: Keycode to emit.
>>> +
>>> +[0]: Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
>>> +[1]: Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt
>>> +[2]: Documentation/devicetree/bindings/gpio/gpio.txt
>>> +
>>> +Example:
>>> +&i2c0 {
>>> +	[...]
>>> +
>>> +	tsc@24 {
>>
>> touchscreen@24
>>
>>> +		compatible = "cypress,cyttsp5";
>>> +		reg = <0x24>;
>>> +
>>> +		pinctrl-names = "default";
>>> +		pinctrl-0 = <&tp_reset_ds203>;
>>> +		interrupt-parent = <&pio>;
>>> +		interrupts = <1 5 IRQ_TYPE_LEVEL_LOW>;
>>> +		reset-gpios = <&pio 7 1 GPIO_ACTIVE_HIGH>;
>>> +
>>> +		button@0 {
>>
>> unit addresses need a reg property. If 0,1,2 are meaningful numbers for
>> the hardware, then it makes sense to add here.
>
> Another option would be just say:
>
> 		linux,keycodes = <KEY_HOMEPAGE>, <KEY_MENU>, <KEY_BACK>;

Sure. I noticed the "linux,code" property so I used that one but I did 
not see the "linux,keycodes". I guess it is possible to group all the 
keycodes using that property.

>
> I am wondering though: you read number of button supported by the device
> from HID_SYSINFO_BTN_OFFSET, can you also get button assignment form
> the device as well?

For what I know, it is not possible. We can only retrieve the number of 
buttons configured for one device but not keycodes.

>
> And the biggest question of all: since you refer to HID descriptors in
> your driver, is it a HID device and should it be driven by HID susbystem
> instead of relying on a custom driver?

I am not familiar with HID subsytem but I looked to other HID drivers 
and read the kernel documentation.
In the datasheet, there is no reference to the HID specification and, 
for example, there is no GET/SET_REPORT requests. There is one "HID 
descriptor register" but that is all.

I guess that it is not a HID device but do not hesitate to give me hints 
to look at it, if you want me to confirm it.

>
>>
>>> +			linux,code = <KEY_HOMEPAGE>;
>>> +		};
>>> +
>>> +		button@1 {
>>> +			linux,code = <KEY_MENU>;
>>> +		};
>>> +
>>> +		button@2 {
>>> +			linux,code = <KEY_BACK>;
>>> +		};
>>> +	};
>>> +};
>>> --
>>> 2.11.0
>>>
>
> Thanks.
>

Best regards,

-- 
Mylène Josserand, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com