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Message-ID: <ZRp9RE2jOZdL0+1/@gofer.mess.org>
Date: Mon, 2 Oct 2023 09:20:20 +0100
From: Sean Young <sean@...s.org>
To: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
Thierry Reding <thierry.reding@...il.com>,
Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>, 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 Mon, Oct 02, 2023 at 08:49:47AM +0300, Ivaylo Dimitrov wrote:
> 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.
It does not work without it - the process doing the 2nd tx hangs indefinitely.
> > 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
This requires keeping a copy of pwm_state in pwm_ir but does avoid the extra
call to pwm_apply_state() here.
Having said that, the extra call to pwm_apply_state() may have benefits,
see this comment in the pwm-sifive driver:
* - When changing both duty cycle and period, we cannot prevent in
* software that the output might produce a period with mixed
* settings (new period length and old duty cycle).
So setting the duty cycle and period once with enabled = false prevents a
first period with mixed settings (i.e. bogus).
> > - 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?
Otherwise the timings are a little off for the first edge - hrtimer setup
time, I think. I can experiment again.
> > - 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);
Requires a copy of pwm_state in pwm_ir, not a huge difference (copy of 28
bytes vs keeping it around).
> > + 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.
If the ir-rx51 driver uses a sleeping pwm then that's broken and only works
by accident - the current driver is broken then.
Spinning for longer periods (e.g. 100us) does not play well with RT. Would
make more sense to fix the pwm driver to non-sleeping when a pwm driver
is used for pwm-ir-tx?
Thanks
Sean
>
> > 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
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