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

[Paul Cercueil <paul@xxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxx>
> > ---
> >  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.

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