Re: [PATCH v6 4/4] media: pwm-ir-tx: trigger edges from hrtimer interrupt context

Thierry Reding
2023-12-08T16:30:04Z

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On Wed, Nov 29, 2023 at 09:13:37AM +0000, Sean Young wrote:
> This makes the generated IR much more precise. Before this change, the
> driver is unreliable and many users opted to use gpio-ir-tx instead.
>
> Signed-off-by: Sean Young <sean@mess.org>
> ---
> drivers/media/rc/pwm-ir-tx.c | 79 ++++++++++++++++++++++++++++++++++--
> 1 file changed, 76 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/rc/pwm-ir-tx.c b/drivers/media/rc/pwm-ir-tx.c
> index cf51e2760975..8575c4596d7b 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 +19,14 @@
>
> struct pwm_ir {
> struct pwm_device *pwm;
> - unsigned int carrier;
> - unsigned int duty_cycle;
> + struct hrtimer timer;
> + struct completion tx_done;
> + struct pwm_state *state;
> + u32 carrier;
> + u32 duty_cycle;
> + uint *txbuf;

Maybe mark this as const to signal that it's not going to get modified?

> + uint txbuf_len;
> + uint txbuf_index;

uint is rather rare. Or so I thought. There seem to be quite a few
occurrences throughout the kernel. I'd still prefer unsigned int over
this abbreviated form, but ultimately up to you and Mauro to decide.

> };
>
> static const struct of_device_id pwm_ir_of_match[] = {
> @@ -82,6 +90,62 @@ static int pwm_ir_tx(struct rc_dev *dev, unsigned int *txbuf,
> return count;
> }
>
> +static int pwm_ir_tx_atomic(struct rc_dev *dev, unsigned int *txbuf,
> + unsigned int count)
> +{
> + struct pwm_ir *pwm_ir = dev->priv;
> + struct pwm_device *pwm = pwm_ir->pwm;
> + struct pwm_state state;
> +
> + 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);
> +
> + pwm_ir->txbuf = txbuf;
> + pwm_ir->txbuf_len = count;
> + pwm_ir->txbuf_index = 0;
> + pwm_ir->state = &state;
> +
> + hrtimer_start(&pwm_ir->timer, 0, HRTIMER_MODE_REL);
> +
> + wait_for_completion(&pwm_ir->tx_done);
> +
> + 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;
> +
> + pwm_ir->state->enabled = !(pwm_ir->txbuf_index % 2);
> + pwm_apply_atomic(pwm_ir->pwm, pwm_ir->state);
> +
> + if (pwm_ir->txbuf_index >= pwm_ir->txbuf_len) {
> + complete(&pwm_ir->tx_done);
> +
> + return HRTIMER_NORESTART;
> + }
> +
> + 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;
> @@ -103,10 +167,19 @@ static int pwm_ir_probe(struct platform_device *pdev)
> if (!rcdev)
> return -ENOMEM;
>
> + if (pwm_is_atomic(pwm_ir->pwm)) {
> + init_completion(&pwm_ir->tx_done);
> + hrtimer_init(&pwm_ir->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + pwm_ir->timer.function = pwm_ir_timer;
> + rcdev->tx_ir = pwm_ir_tx_atomic;
> + } else {
> + dev_info(&pdev->dev, "tx will not be accurate as pwm device does not support atomic mode");

s/tx/TX and s/pwm/PWM/? Also, I'm a bit unhappy about "atomic mode" here
because the term is overloaded in PWM. If you call pwm_appy_*() then by
definition it's going to be "atomic" in the "atomic state" sense. So
maybe switch to something like:

"TX will not be accurate as PWM device might sleep"

?

Thierry

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