Re: [PATCH] Input: ili210x - Improve polled sample spacing

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Hi Marek,

On Mon, Nov 08, 2021 at 01:52:16AM +0100, Marek Vasut wrote:
> Currently the ili210x driver implements a threaded interrupt handler which
> starts upon edge on the interrupt line, and then polls the touch controller
> for samples. Every time a sample is obtained from the controller, the thread
> function checks whether further polling is required, and if so, waits fixed
> amount of time before polling for next sample.
> 
> The delay between consecutive samples can thus vary greatly, because the
> I2C transfer required to retrieve the sample from the controller takes
> different amount of time on different platforms. Furthermore, different
> models of the touch controllers supported by this driver require different
> delays during retrieval of samples too.
> 
> Instead of waiting fixed amount of time before polling for next sample,
> determine how much time passed since the beginning of sampling cycle and
> then wait only the remaining amount of time within the sampling cycle.
> This makes the driver deliver samples with equal spacing between them.
> 
> Signed-off-by: Marek Vasut <marex@denx.de>
> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> Cc: Joe Hung <joe_hung@ilitek.com>
> Cc: Luca Hsu <luca_hsu@ilitek.com>
> ---
>  drivers/input/touchscreen/ili210x.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/ili210x.c b/drivers/input/touchscreen/ili210x.c
> index a3b71a9511eb3..b2d9fe1e1c707 100644
> --- a/drivers/input/touchscreen/ili210x.c
> +++ b/drivers/input/touchscreen/ili210x.c
> @@ -328,10 +328,13 @@ static irqreturn_t ili210x_irq(int irq, void *irq_data)
>  	const struct ili2xxx_chip *chip = priv->chip;
>  	u8 touchdata[ILI210X_DATA_SIZE] = { 0 };
>  	bool keep_polling;
> +	ktime_t time_next;
> +	s64 time_delta;
>  	bool touch;
>  	int error;
>  
>  	do {
> +		time_next = ktime_add_ms(ktime_get(), ILI2XXX_POLL_PERIOD);
>  		error = chip->get_touch_data(client, touchdata);
>  		if (error) {
>  			dev_err(&client->dev,
> @@ -341,8 +344,11 @@ static irqreturn_t ili210x_irq(int irq, void *irq_data)
>  
>  		touch = ili210x_report_events(priv, touchdata);
>  		keep_polling = chip->continue_polling(touchdata, touch);
> -		if (keep_polling)
> -			msleep(ILI2XXX_POLL_PERIOD);
> +		if (keep_polling) {
> +			time_delta = ktime_us_delta(time_next, ktime_get());

Do we really need to use exact time, or ktime_get_coarse() is good
enough, as it is cheaper?

> +			if (time_delta > 0)
> +				usleep_range(time_delta, time_delta + 1000);
> +		}
>  	} while (!priv->stop && keep_polling);
>  
>  	return IRQ_HANDLED;
> -- 
> 2.33.0
> 

Thanks.

-- 
Dmitry