linux-kernel - Re: [PATCH 2/2] media: pwm-ir-tx: trigger edges from hrtimer interrupt context

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Date:   Mon, 2 Oct 2023 08:49:47 +0300
From:   Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
To:     Sean Young <sean@...s.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org
Subject: Re: [PATCH 2/2] media: pwm-ir-tx: trigger edges from hrtimer
 interrupt context

Hi,

On 1.10.23 г. 13:40 ч., Sean Young wrote:
> The pwm-ir-tx driver has to turn the pwm signal on and off, and suffers
> from delays as this is done in process context. Make this work in atomic
> context.
> 
> This makes the driver much more precise.
> 
> Signed-off-by: Sean Young <sean@...s.org>
> Cc: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
> ---
>   drivers/media/rc/pwm-ir-tx.c | 79 ++++++++++++++++++++++++++++--------
>   1 file changed, 63 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/media/rc/pwm-ir-tx.c b/drivers/media/rc/pwm-ir-tx.c
> index c5f37c03af9c..557725a07a67 100644
> --- a/drivers/media/rc/pwm-ir-tx.c
> +++ b/drivers/media/rc/pwm-ir-tx.c
> @@ -10,6 +10,8 @@
>   #include <linux/slab.h>
>   #include <linux/of.h>
>   #include <linux/platform_device.h>
> +#include <linux/hrtimer.h>
> +#include <linux/completion.h>
>   #include <media/rc-core.h>
>   
>   #define DRIVER_NAME	"pwm-ir-tx"
> @@ -17,8 +19,13 @@
>   
>   struct pwm_ir {
>   	struct pwm_device *pwm;
> -	unsigned int carrier;
> -	unsigned int duty_cycle;
> +	struct hrtimer timer;
> +	struct completion completion;
> +	uint carrier;
> +	uint duty_cycle;
> +	uint *txbuf;
> +	uint txbuf_len;
> +	uint txbuf_index;
>   };
>   
>   static const struct of_device_id pwm_ir_of_match[] = {
> @@ -55,33 +62,65 @@ static int pwm_ir_tx(struct rc_dev *dev, unsigned int *txbuf,
>   	struct pwm_ir *pwm_ir = dev->priv;
>   	struct pwm_device *pwm = pwm_ir->pwm;
>   	struct pwm_state state;
> -	int i;
> -	ktime_t edge;
> -	long delta;
> +
> +	reinit_completion(&pwm_ir->completion);

You should not need that.

>   
>   	pwm_init_state(pwm, &state);
>   
>   	state.period = DIV_ROUND_CLOSEST(NSEC_PER_SEC, pwm_ir->carrier);
>   	pwm_set_relative_duty_cycle(&state, pwm_ir->duty_cycle, 100);
> +	state.enabled = false;
>   
> -	edge = ktime_get();
> +	pwm_ir->txbuf = txbuf;
> +	pwm_ir->txbuf_len = count;
> +	pwm_ir->txbuf_index = 0;
>   
> -	for (i = 0; i < count; i++) {
> -		state.enabled = !(i % 2);
> -		pwm_apply_state(pwm, &state);
> +	pwm_apply_state(pwm, &state);
>   

ditto, first pwm control should be in the timer function

> -		edge = ktime_add_us(edge, txbuf[i]);
> -		delta = ktime_us_delta(edge, ktime_get());
> -		if (delta > 0)
> -			usleep_range(delta, delta + 10);
> -	}
> +	hrtimer_start(&pwm_ir->timer, 1000, HRTIMER_MODE_REL);
>   

why not just call it with 0 time?

> -	state.enabled = false;
> -	pwm_apply_state(pwm, &state);
> +	wait_for_completion(&pwm_ir->completion);
>   
>   	return count;
>   }
>   
> +static enum hrtimer_restart pwm_ir_timer(struct hrtimer *timer)
> +{
> +	struct pwm_ir *pwm_ir = container_of(timer, struct pwm_ir, timer);
> +	ktime_t now;
> +
> +	/*
> +	 * If we happen to hit an odd latency spike, loop through the
> +	 * pulses until we catch up.
> +	 */
> +	do {
> +		u64 ns;
> +
> +		if (pwm_ir->txbuf_index >= pwm_ir->txbuf_len) {
> +			/* Stop TX here */
> +			pwm_disable(pwm_ir->pwm);
> +
> +			complete(&pwm_ir->completion);
> +
> +			return HRTIMER_NORESTART;
> +		}
> +
> +		if (pwm_ir->txbuf_index % 2)
> +			pwm_disable(pwm_ir->pwm);
> +		else
> +			pwm_enable(pwm_ir->pwm);
> +

pwm_ir->pwm->state.enabled = !(pwm_ir->txbuf_index % 2);
pwm_apply_state(pwm_ir->pwm, pwm_ir->state);

> +		ns = US_TO_NS(pwm_ir->txbuf[pwm_ir->txbuf_index]);
> +		hrtimer_add_expires_ns(timer, ns);
> +
> +		pwm_ir->txbuf_index++;
> +
> +		now = timer->base->get_time();
> +	} while (hrtimer_get_expires_tv64(timer) < now);
> +
> +	return HRTIMER_RESTART;
> +}
> +
>   static int pwm_ir_probe(struct platform_device *pdev)
>   {
>   	struct pwm_ir *pwm_ir;
> @@ -96,8 +135,16 @@ static int pwm_ir_probe(struct platform_device *pdev)
>   	if (IS_ERR(pwm_ir->pwm))
>   		return PTR_ERR(pwm_ir->pwm);
>   
> +	if (pwm_can_sleep(pwm_ir->pwm)) {
> +		dev_err(&pdev->dev, "unsupported pwm device: driver can sleep\n");
> +		return -ENODEV;
> +	}
> +

I think we shall not limit, but use high priority thread to support 
those drivers. I have that working on n900 with current (sleeping) pwm, 
see my reply on the other mail. Maybe we can combine both patches in a 
way to support both atomic and sleeping pwm drivers.

>   	pwm_ir->carrier = 38000;
>   	pwm_ir->duty_cycle = 50;
> +	init_completion(&pwm_ir->completion);
> +	hrtimer_init(&pwm_ir->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	pwm_ir->timer.function = pwm_ir_timer;
>   
>   	rcdev = devm_rc_allocate_device(&pdev->dev, RC_DRIVER_IR_RAW_TX);
>   	if (!rcdev)
> 

Regards,
Ivo