linux-kernel - Re: [PATCH] input: goodix: Poll the 'buffer status' bit before reading data

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Message-ID: <b6ecb1aaa46370727a565e76c6d5925c@crapouillou.net>
Date:   Fri, 31 Mar 2017 12:18:47 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Bastien Nocera <hadess@...ess.net>, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] input: goodix: Poll the 'buffer status' bit before
 reading data

Hi,

Le 2017-03-31 00:48, Dmitry Torokhov a écrit :
> On Thu, Mar 30, 2017 at 03:33:49PM +0200, Paul Cercueil wrote:
>> The Goodix panel triggers an interrupt on touch events. However, its
>> registers will contain the valid values a short time after the
>> interrupt, and not when it's raised. At that moment, the 'buffer 
>> status'
>> bit is set.
> 
> Yay for awesome hardware.
> 
>> 
>> Previously, if the 'buffer status' bit was not set when the registers
>> were read, the data was discarded and no input event was emitted,
>> causing "finger down" or "finger up" events to be missed sometimes.
>> 
>> This went unnoticed until v4.9, as the DesignWare I2C driver commonly
>> used with this driver had enough latency for that bug to never 
>> trigger.
>> 
>> Now, in the IRQ handler we will poll (with a timeout) the 'buffer 
>> status'
>> bit and process the data of the panel as soon as this bit gets set.
>> 
>> Note that the Goodix panel will send a few spurious interrupts after 
>> the
>> 'finger up' event, in which the 'buffer status' bit will never be set.
>> 
>> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>> ---
>>  drivers/input/touchscreen/goodix.c | 30 
>> +++++++++++++++++++++++-------
>>  1 file changed, 23 insertions(+), 7 deletions(-)
>> 
>> diff --git a/drivers/input/touchscreen/goodix.c 
>> b/drivers/input/touchscreen/goodix.c
>> index 240b16f3ee97..7a8b89b87c2f 100644
>> --- a/drivers/input/touchscreen/goodix.c
>> +++ b/drivers/input/touchscreen/goodix.c
>> @@ -195,18 +195,34 @@ static int goodix_get_cfg_len(u16 id)
>> 
>>  static int goodix_ts_read_input_report(struct goodix_ts_data *ts, u8 
>> *data)
>>  {
>> +	unsigned int timeout = 100;
>>  	int touch_num;
>>  	int error;
>> 
>> -	error = goodix_i2c_read(ts->client, GOODIX_READ_COOR_ADDR, data,
>> +	/* The 'buffer status' bit, which indicates that the data is valid, 
>> is
>> +	 * not set as soon as the interrupt is raised, but slightly after.
>> +	 */
>> +	do {
>> +		error = goodix_i2c_read(ts->client, GOODIX_READ_COOR_ADDR, data,
>>  				GOODIX_CONTACT_SIZE + 1);
>> -	if (error) {
>> -		dev_err(&ts->client->dev, "I2C transfer error: %d\n", error);
>> -		return error;
>> -	}
>> +		if (error) {
>> +			dev_err(&ts->client->dev, "I2C transfer error: %d\n",
>> +					error);
>> +			return error;
>> +		}
>> 
>> -	if (!(data[0] & 0x80))
>> -		return -EAGAIN;
>> +		if (data[0] & 0x80)
>> +			break;
>> +
>> +		usleep_range(100, 200);
> 
> What is the typical delay between IRQ and data being ready? 100 repeats
> suggest that poll interval is too small.
> 

On my panel it seems to be about 10ms - which sounds like a *huge* lot 
of time...

>> +	} while (--timeout);
>> +
>> +	if (!timeout) {
>> +		/* The Goodix panel will send spurious interrupts after a
>> +		 * 'finger up' event, which will always cause a timeout.
>> +		 */
>> +		return 0;
>> +	}
>> 
>>  	touch_num = data[0] & 0x0f;
>>  	if (touch_num > ts->max_touch_num)
>> --
>> 2.11.0
>> 
> 
> Thanks.