linux-kernel - Re: [PATCH v2 4/8] Input: pixcir_i2c_ts: Use Type-B Multi-Touch protocol

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Date:	Mon, 10 Mar 2014 10:57:10 +0200
From:	Roger Quadros <rogerq@...com>
To:	Henrik Rydberg <rydberg@...omail.se>, <dmitry.torokhov@...il.com>
CC:	<jcbian@...cir.com.cn>, <balbi@...com>, <dmurphy@...com>,
	<mugunthanvnm@...com>, <linux-input@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 4/8] Input: pixcir_i2c_ts: Use Type-B Multi-Touch protocol

Hi Henrik,

On 03/08/2014 05:11 PM, Henrik Rydberg wrote:
> Hi Roger,
> 
> the MT implementation seems mostly fine, just one curiosity:
> 
>>  static irqreturn_t pixcir_ts_isr(int irq, void *dev_id)
>>  {
>>  	struct pixcir_i2c_ts_data *tsdata = dev_id;
>>  	const struct pixcir_ts_platform_data *pdata = tsdata->chip;
>> +	struct pixcir_report_data report;
>>  
>>  	while (!tsdata->exiting) {
>> -		pixcir_ts_poscheck(tsdata);
>> -
>> -		if (gpio_get_value(pdata->gpio_attb))
>> +		/* parse packet */
>> +		pixcir_ts_parse(tsdata, &report);
>> +
>> +		/* report it */
>> +		pixcir_ts_report(tsdata, &report);
>> +
>> +		if (gpio_get_value(pdata->gpio_attb)) {
>> +			if (report.num_touches) {
>> +				/*
>> +				 * Last report with no finger up?
>> +				 * Do it now then.
>> +				 */
>> +				input_mt_sync_frame(tsdata->input);
>> +				input_sync(tsdata->input);
> 
> Why is this special handling needed?

This is needed because the controller doesn't always report when all fingers
have left the screen. e.g. report might contain 3 fingers touched and then
gpio_attb line is de-asserted. There's no report with 0 fingers touched even
if the user's fingers have left the screen. So we never detect a BUTTON_UP.

Without this s/w workaround we observe side effects like buttons being pressed
but not released. To me it looks like a bug in the controller.

cheers,
-roger
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