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pwm: atmel: Rework tracking updates pending in hardware

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This improves the driver's behavior in several ways:

 - The lock is held for shorter periods and so a channel that is currently
   waited for doesn't block disabling another channel.

 - It's easier to understand because the procedure is split into more
   semantic units and documentation is improved

 - A channel is only set to pending when such an event is actually
   scheduled in hardware (by writing the CUPD register).

 - Also wait in .get_state() to report the last configured state instead
   of (maybe) the previous one. This fixes the read back duty cycle and so
   prevents a warning being emitted when PWM_DEBUG is on.

Tested on an AriettaG25.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
This commit is contained in:
Uwe Kleine-König 2021-04-21 11:26:08 +02:00 committed by Thierry Reding
parent 2734d6c1b1
commit 52eaba4ced
1 changed files with 79 additions and 23 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

102
drivers/pwm/pwm-atmel.c
View file

@ -84,9 +84,19 @@ struct atmel_pwm_chip {
void __iomem *base;
const struct atmel_pwm_data *data;
unsigned int updated_pwms;
/* ISR is cleared when read, ensure only one thread does that */
struct mutex isr_lock;
/*
* The hardware supports a mechanism to update a channel's duty cycle at
* the end of the currently running period. When such an update is
* pending we delay disabling the PWM until the new configuration is
* active because otherwise pmw_config(duty_cycle=0); pwm_disable();
* might not result in an inactive output.
* This bitmask tracks for which channels an update is pending in
* hardware.
*/
u32 update_pending;
/* Protects .update_pending */
spinlock_t lock;
};
static inline struct atmel_pwm_chip *to_atmel_pwm_chip(struct pwm_chip *chip)
@ -123,6 +133,64 @@ static inline void atmel_pwm_ch_writel(struct atmel_pwm_chip *chip,
atmel_pwm_writel(chip, base + offset, val);
}
static void atmel_pwm_update_pending(struct atmel_pwm_chip *chip)
{
/*
* Each channel that has its bit in ISR set started a new period since
* ISR was cleared and so there is no more update pending. Note that
* reading ISR clears it, so this needs to handle all channels to not
* loose information.
*/
u32 isr = atmel_pwm_readl(chip, PWM_ISR);
chip->update_pending &= ~isr;
}
static void atmel_pwm_set_pending(struct atmel_pwm_chip *chip, unsigned int ch)
{
spin_lock(&chip->lock);
/*
* Clear pending flags in hardware because otherwise there might still
* be a stale flag in ISR.
*/
atmel_pwm_update_pending(chip);
chip->update_pending |= (1 << ch);
spin_unlock(&chip->lock);
}
static int atmel_pwm_test_pending(struct atmel_pwm_chip *chip, unsigned int ch)
{
int ret = 0;
spin_lock(&chip->lock);
if (chip->update_pending & (1 << ch)) {
atmel_pwm_update_pending(chip);
if (chip->update_pending & (1 << ch))
ret = 1;
}
spin_unlock(&chip->lock);
return ret;
}
static int atmel_pwm_wait_nonpending(struct atmel_pwm_chip *chip, unsigned int ch)
{
unsigned long timeout = jiffies + 2 * HZ;
int ret;
while ((ret = atmel_pwm_test_pending(chip, ch)) &&
time_before(jiffies, timeout))
usleep_range(10, 100);
return ret ? -ETIMEDOUT : 0;
}
static int atmel_pwm_calculate_cprd_and_pres(struct pwm_chip *chip,
unsigned long clkrate,
const struct pwm_state *state,
@ -185,6 +253,7 @@ static void atmel_pwm_update_cdty(struct pwm_chip *chip, struct pwm_device *pwm,
atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm,
atmel_pwm->data->regs.duty_upd, cdty);
atmel_pwm_set_pending(atmel_pwm, pwm->hwpwm);
}
static void atmel_pwm_set_cprd_cdty(struct pwm_chip *chip,
@ -205,20 +274,8 @@ static void atmel_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm,
struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
unsigned long timeout = jiffies + 2 * HZ;
/*
* Wait for at least a complete period to have passed before disabling a
* channel to be sure that CDTY has been updated
*/
mutex_lock(&atmel_pwm->isr_lock);
atmel_pwm->updated_pwms |= atmel_pwm_readl(atmel_pwm, PWM_ISR);
atmel_pwm_wait_nonpending(atmel_pwm, pwm->hwpwm);
while (!(atmel_pwm->updated_pwms & (1 << pwm->hwpwm)) &&
time_before(jiffies, timeout)) {
usleep_range(10, 100);
atmel_pwm->updated_pwms |= atmel_pwm_readl(atmel_pwm, PWM_ISR);
}
mutex_unlock(&atmel_pwm->isr_lock);
atmel_pwm_writel(atmel_pwm, PWM_DIS, 1 << pwm->hwpwm);
/*
@ -292,10 +349,6 @@ static int atmel_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
val |= PWM_CMR_CPOL;
atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, val);
atmel_pwm_set_cprd_cdty(chip, pwm, cprd, cdty);
mutex_lock(&atmel_pwm->isr_lock);
atmel_pwm->updated_pwms |= atmel_pwm_readl(atmel_pwm, PWM_ISR);
atmel_pwm->updated_pwms &= ~(1 << pwm->hwpwm);
mutex_unlock(&atmel_pwm->isr_lock);
atmel_pwm_writel(atmel_pwm, PWM_ENA, 1 << pwm->hwpwm);
} else if (cstate.enabled) {
atmel_pwm_disable(chip, pwm, true);
@ -326,6 +379,9 @@ static void atmel_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
tmp <<= pres;
state->period = DIV64_U64_ROUND_UP(tmp, rate);
/* Wait for an updated duty_cycle queued in hardware */
atmel_pwm_wait_nonpending(atmel_pwm, pwm->hwpwm);
cdty = atmel_pwm_ch_readl(atmel_pwm, pwm->hwpwm,
atmel_pwm->data->regs.duty);
tmp = (u64)(cprd - cdty) * NSEC_PER_SEC;
@ -416,9 +472,10 @@ static int atmel_pwm_probe(struct platform_device *pdev)
if (!atmel_pwm)
return -ENOMEM;
mutex_init(&atmel_pwm->isr_lock);
atmel_pwm->data = of_device_get_match_data(&pdev->dev);
atmel_pwm->updated_pwms = 0;
atmel_pwm->update_pending = 0;
spin_lock_init(&atmel_pwm->lock);
atmel_pwm->base = devm_platform_ioremap_resource(pdev, 0);
if (IS_ERR(atmel_pwm->base))
@ -460,7 +517,6 @@ static int atmel_pwm_remove(struct platform_device *pdev)
pwmchip_remove(&atmel_pwm->chip);
clk_unprepare(atmel_pwm->clk);
mutex_destroy(&atmel_pwm->isr_lock);
return 0;
}