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SubjectRe: [PATCH] input: goodix: Poll the 'buffer status' bit before reading data
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@crapouillou.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.

> + } 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.

--
Dmitry

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