linux-kernel - Re: [PATCH 2/3] Input: of_touchscreen - fix setting max values on X/Y axis

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Message-ID: <559E318B.4030106@ti.com>
Date:	Thu, 9 Jul 2015 11:32:11 +0300
From:	Roger Quadros <rogerq@...com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	<linux-input@...r.kernel.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Sebastian Reichel <sre@...nel.org>,
	Pavel Machek <pavel@....cz>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] Input: of_touchscreen - fix setting max values on
 X/Y axis

Dmitry,

On 08/07/15 18:08, Dmitry Torokhov wrote:
> On Wed, Jul 08, 2015 at 10:59:04AM +0300, Roger Quadros wrote:
>> Dmitry,
>>
>> On 07/07/15 19:25, Dmitry Torokhov wrote:
>>> Hi Roger,
>>>
>>> On Tue, Jul 07, 2015 at 12:37:31PM +0300, Roger Quadros wrote:
>>>> Hi Dmitry,
>>>>
>>>> On 07/07/15 03:27, Dmitry Torokhov wrote:
>>>>> The binding specification says that "touchscreen-size-x" and "-y" specify
>>>>> horizontal and vertical resolution of the touchscreen and therefore maximum
>>>>> absolute coordinates should be reduced by 1 since we are starting with 0.
>>>>>
>>>>> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
>>>>> ---
>>>>>  drivers/input/touchscreen/of_touchscreen.c | 10 ++++++----
>>>>>  1 file changed, 6 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/drivers/input/touchscreen/of_touchscreen.c b/drivers/input/touchscreen/of_touchscreen.c
>>>>> index 759cf4b..50bc0f2 100644
>>>>> --- a/drivers/input/touchscreen/of_touchscreen.c
>>>>> +++ b/drivers/input/touchscreen/of_touchscreen.c
>>>>> @@ -71,23 +71,25 @@ void touchscreen_parse_of_params(struct input_dev *dev, bool multitouch)
>>>>>
>>>>>  	axis = multitouch ? ABS_MT_POSITION_X : ABS_X;
>>>>>  	data_present = touchscreen_get_prop_u32(np, "touchscreen-size-x",
>>>>> -						input_abs_get_max(dev, axis),
>>>>> +						input_abs_get_max(dev,
>>>>> +								  axis) + 1,
>>>>
>>>> Why do we need to pass default_value to touchscreen_get_prop_u32()?
>>>> If the property doesn't exist we are not updating the parameter
>>>> anyway right?
>>>
>>> The binding can specify max, fuzz, both, or neither. If only one is
>>> specified we do not want to "undo" whatever the driver did (for example
>>
>> why not? At least that is not what touchscreen_parse_properties() does.
>> It will update the touchscreen params if any one of the DT property
>> is present.
> 
> Yes, but while keeping the old properties (max, fuzz) intact if they
> have not been specified in dts. That is why we are passing default value
> to touchscreen_get_prop_u32.
> 
>>
>>> tsc2005 sets up the default maximums before trying to parse OF), so we
>>> fetch the current value and pass it on as default one.
>>
>> This is what would happen in tsc2005 case
>>
>> -driver first sets ABS_X_max to 0xfff and ABS_Y_max to 0xfff.
>> -calls touchscreen_parse_properties()
>> -which calls touchscreen_get_prop_u32(dev, "touchscreen-size-x",
>> 0xfff+1, &maximum)
>> -if DT properties are missing, touchscreen_get_prop_u32() changes
>> ABS_X_max to 0x1000 and returns false.
>> - as data_present is false we don't do a -1 and so we have ABS_X_max
>> changed to 0x1000.
> 
> If data_present is false we do not call input_set_abs_params() at all
> ans so nothing changes in input device settings.  Now, if fuzz would be

You are right. I missed the fact that we don't call input_set_abs_params()
in data_present is false case hence my confusion.

> set up (but size was not) we would be calling input_set_abs_params(),
> but given that we subtract 1 from maximum returned by
> touchscreen_get_prop_u32() we'd be setting input_set_abs_params(input,
> ABS_X, 0, 0x1000 - 1, fuzz) thus preserving 0xfff value set by the
> driver.
> 
>>
>> This doesn't look right.
>>
>> So IMO default_value parameter can be removed from
>> touchscreen_get_prop_u32() to make things simpler.
>>
>> If the property doesn't exist it will not change *value and return false.
> 
> But it will change if one of the properties set. For example, if you set
> fuzz but not size.

Yes. Thanks for explaining :).

cheers,
-roger
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