Subject: Re: [PATCH v2] iio: trigger: stm32-timer: enable clock when in master mode

From: Jonathan Cameron <[email-masked]>
Date: Fri, 14 Feb 2020 15:14:08 +0000

On Fri, 14 Feb 2020 15:50:57 +0100
Fabrice Gasnier <[email-masked]> wrote:

> On 2/14/20 3:20 PM, Jonathan Cameron wrote:
> > On Fri, 7 Feb 2020 17:30:31 +0100
> > Fabrice Gasnier <[email-masked]> wrote:
> >   
> >> Clock should be enabled as soon as using master modes, even before
> >> enabling timer. Or, this may provoke bad behavior on the other end
> >> (slave timer). Then, introduce 'clk_enabled' flag, instead of relying
> >> on CR1 EN bit, to keep track of clock being enabled (balanced refcount).
> >> Propagate this anywhere else in the driver.
> >>
> >> Also add 'remove' routine to stop timer and disable clock in case it
> >> has been left enabled. Enforce the user interface has been unregistered
> >> in the remove routine, before disabling the hardware to avoid possible
> >> race. So, remove use of devm_ variant to register triggers and unregister
> >> them before the hardware gets disabled [1].
> >> [1] https://patchwork.kernel.org/patch/9956247/
> >>
> >> Signed-off-by: Fabrice Gasnier <[email-masked]>  
> > Patch looks fine. So is this a fix for a known issue or a theoretical one?
> > Just a question of whether to line it up for an rc, or wait for next
> > merge window.  Ideally please give me a fixes tag as well if this
> > fixes a problem that is being seen in the wild.  
> 
> Hi Jonathan,
> 
> I got no complain for now. So I think this is fine to wait for the next
> merge window.
Hi Fabrice,

Great.  Unfortunately this has crossed with other changes on the driver.
Would you mind doing a rebase on my testing branch?  It looked fairly
simple but I wasn't totally confident to do it without being able
to test!

Thanks,

Jonathan

> 
> Thanks,
> Fabrice
> 
> > 
> > Thanks,
> > 
> > Jonathan
> >   
> >> ---
> >> Changes in v2:
> >> - enforce the user interface has been unregistered in the remove routine,
> >>   before disabling the hardware to avoid possible race.
> >> ---
> >>  drivers/iio/trigger/stm32-timer-trigger.c | 98 ++++++++++++++++++++++++-------
> >>  1 file changed, 76 insertions(+), 22 deletions(-)
> >>
> >> diff --git a/drivers/iio/trigger/stm32-timer-trigger.c b/drivers/iio/trigger/stm32-timer-trigger.c
> >> index a5dfe65..473853e 100644
> >> --- a/drivers/iio/trigger/stm32-timer-trigger.c
> >> +++ b/drivers/iio/trigger/stm32-timer-trigger.c
> >> @@ -79,10 +79,13 @@ struct stm32_timer_trigger {
> >>  	struct device *dev;
> >>  	struct regmap *regmap;
> >>  	struct clk *clk;
> >> +	bool clk_enabled;
> >>  	u32 max_arr;
> >>  	const void *triggers;
> >>  	const void *valids;
> >>  	bool has_trgo2;
> >> +	struct mutex lock; /* concurrent sysfs configuration */
> >> +	struct list_head tr_list;
> >>  };
> >>  
> >>  struct stm32_timer_trigger_cfg {
> >> @@ -106,7 +109,7 @@ static int stm32_timer_start(struct stm32_timer_trigger *priv,
> >>  {
> >>  	unsigned long long prd, div;
> >>  	int prescaler = 0;
> >> -	u32 ccer, cr1;
> >> +	u32 ccer;
> >>  
> >>  	/* Period and prescaler values depends of clock rate */
> >>  	div = (unsigned long long)clk_get_rate(priv->clk);
> >> @@ -136,9 +139,11 @@ static int stm32_timer_start(struct stm32_timer_trigger *priv,
> >>  	if (ccer & TIM_CCER_CCXE)
> >>  		return -EBUSY;
> >>  
> >> -	regmap_read(priv->regmap, TIM_CR1, &cr1);
> >> -	if (!(cr1 & TIM_CR1_CEN))
> >> +	mutex_lock(&priv->lock);
> >> +	if (!priv->clk_enabled) {
> >> +		priv->clk_enabled = true;
> >>  		clk_enable(priv->clk);
> >> +	}
> >>  
> >>  	regmap_write(priv->regmap, TIM_PSC, prescaler);
> >>  	regmap_write(priv->regmap, TIM_ARR, prd - 1);
> >> @@ -157,22 +162,20 @@ static int stm32_timer_start(struct stm32_timer_trigger *priv,
> >>  
> >>  	/* Enable controller */
> >>  	regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN, TIM_CR1_CEN);
> >> +	mutex_unlock(&priv->lock);
> >>  
> >>  	return 0;
> >>  }
> >>  
> >>  static void stm32_timer_stop(struct stm32_timer_trigger *priv)
> >>  {
> >> -	u32 ccer, cr1;
> >> +	u32 ccer;
> >>  
> >>  	regmap_read(priv->regmap, TIM_CCER, &ccer);
> >>  	if (ccer & TIM_CCER_CCXE)
> >>  		return;
> >>  
> >> -	regmap_read(priv->regmap, TIM_CR1, &cr1);
> >> -	if (cr1 & TIM_CR1_CEN)
> >> -		clk_disable(priv->clk);
> >> -
> >> +	mutex_lock(&priv->lock);
> >>  	/* Stop timer */
> >>  	regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_ARPE, 0);
> >>  	regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN, 0);
> >> @@ -181,6 +184,12 @@ static void stm32_timer_stop(struct stm32_timer_trigger *priv)
> >>  
> >>  	/* Make sure that registers are updated */
> >>  	regmap_update_bits(priv->regmap, TIM_EGR, TIM_EGR_UG, TIM_EGR_UG);
> >> +
> >> +	if (priv->clk_enabled) {
> >> +		priv->clk_enabled = false;
> >> +		clk_disable(priv->clk);
> >> +	}
> >> +	mutex_unlock(&priv->lock);
> >>  }
> >>  
> >>  static ssize_t stm32_tt_store_frequency(struct device *dev,
> >> @@ -295,11 +304,18 @@ static ssize_t stm32_tt_store_master_mode(struct device *dev,
> >>  	for (i = 0; i <= master_mode_max; i++) {
> >>  		if (!strncmp(master_mode_table[i], buf,
> >>  			     strlen(master_mode_table[i]))) {
> >> +			mutex_lock(&priv->lock);
> >> +			if (!priv->clk_enabled) {
> >> +				/* Clock should be enabled first */
> >> +				priv->clk_enabled = true;
> >> +				clk_enable(priv->clk);
> >> +			}
> >>  			regmap_update_bits(priv->regmap, TIM_CR2, mask,
> >>  					   i << shift);
> >>  			/* Make sure that registers are updated */
> >>  			regmap_update_bits(priv->regmap, TIM_EGR,
> >>  					   TIM_EGR_UG, TIM_EGR_UG);
> >> +			mutex_unlock(&priv->lock);
> >>  			return len;
> >>  		}
> >>  	}
> >> @@ -357,11 +373,21 @@ static const struct attribute_group *stm32_trigger_attr_groups[] = {
> >>  static const struct iio_trigger_ops timer_trigger_ops = {
> >>  };
> >>  
> >> -static int stm32_setup_iio_triggers(struct stm32_timer_trigger *priv)
> >> +static void stm32_unregister_iio_triggers(struct stm32_timer_trigger *priv)
> >> +{
> >> +	struct iio_trigger *tr;
> >> +
> >> +	list_for_each_entry(tr, &priv->tr_list, alloc_list)
> >> +		iio_trigger_unregister(tr);
> >> +}
> >> +
> >> +static int stm32_register_iio_triggers(struct stm32_timer_trigger *priv)
> >>  {
> >>  	int ret;
> >>  	const char * const *cur = priv->triggers;
> >>  
> >> +	INIT_LIST_HEAD(&priv->tr_list);
> >> +
> >>  	while (cur && *cur) {
> >>  		struct iio_trigger *trig;
> >>  		bool cur_is_trgo = stm32_timer_is_trgo_name(*cur);
> >> @@ -388,9 +414,13 @@ static int stm32_setup_iio_triggers(struct stm32_timer_trigger *priv)
> >>  
> >>  		iio_trigger_set_drvdata(trig, priv);
> >>  
> >> -		ret = devm_iio_trigger_register(priv->dev, trig);
> >> -		if (ret)
> >> +		ret = iio_trigger_register(trig);
> >> +		if (ret) {
> >> +			stm32_unregister_iio_triggers(priv);
> >>  			return ret;
> >> +		}
> >> +
> >> +		list_add_tail(&trig->alloc_list, &priv->tr_list);
> >>  		cur++;
> >>  	}
> >>  
> >> @@ -437,7 +467,6 @@ static int stm32_counter_write_raw(struct iio_dev *indio_dev,
> >>  				   int val, int val2, long mask)
> >>  {
> >>  	struct stm32_timer_trigger *priv = iio_priv(indio_dev);
> >> -	u32 dat;
> >>  
> >>  	switch (mask) {
> >>  	case IIO_CHAN_INFO_RAW:
> >> @@ -448,19 +477,23 @@ static int stm32_counter_write_raw(struct iio_dev *indio_dev,
> >>  		return -EINVAL;
> >>  
> >>  	case IIO_CHAN_INFO_ENABLE:
> >> +		mutex_lock(&priv->lock);
> >>  		if (val) {
> >> -			regmap_read(priv->regmap, TIM_CR1, &dat);
> >> -			if (!(dat & TIM_CR1_CEN))
> >> +			if (!priv->clk_enabled) {
> >> +				priv->clk_enabled = true;
> >>  				clk_enable(priv->clk);
> >> +			}
> >>  			regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN,
> >>  					   TIM_CR1_CEN);
> >>  		} else {
> >> -			regmap_read(priv->regmap, TIM_CR1, &dat);
> >>  			regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN,
> >>  					   0);
> >> -			if (dat & TIM_CR1_CEN)
> >> +			if (priv->clk_enabled) {
> >> +				priv->clk_enabled = false;
> >>  				clk_disable(priv->clk);
> >> +			}
> >>  		}
> >> +		mutex_unlock(&priv->lock);
> >>  		return 0;
> >>  	}
> >>  
> >> @@ -556,7 +589,6 @@ static int stm32_set_enable_mode(struct iio_dev *indio_dev,
> >>  {
> >>  	struct stm32_timer_trigger *priv = iio_priv(indio_dev);
> >>  	int sms = stm32_enable_mode2sms(mode);
> >> -	u32 val;
> >>  
> >>  	if (sms < 0)
> >>  		return sms;
> >> @@ -564,11 +596,12 @@ static int stm32_set_enable_mode(struct iio_dev *indio_dev,
> >>  	 * Triggered mode sets CEN bit automatically by hardware. So, first
> >>  	 * enable counter clock, so it can use it. Keeps it in sync with CEN.
> >>  	 */
> >> -	if (sms == 6) {
> >> -		regmap_read(priv->regmap, TIM_CR1, &val);
> >> -		if (!(val & TIM_CR1_CEN))
> >> -			clk_enable(priv->clk);
> >> +	mutex_lock(&priv->lock);
> >> +	if (sms == 6 && !priv->clk_enabled) {
> >> +		clk_enable(priv->clk);
> >> +		priv->clk_enabled = true;
> >>  	}
> >> +	mutex_unlock(&priv->lock);
> >>  
> >>  	regmap_update_bits(priv->regmap, TIM_SMCR, TIM_SMCR_SMS, sms);
> >>  
> >> @@ -752,8 +785,9 @@ static int stm32_timer_trigger_probe(struct platform_device *pdev)
> >>  	priv->triggers = triggers_table[index];
> >>  	priv->valids = cfg->valids_table[index];
> >>  	stm32_timer_detect_trgo2(priv);
> >> +	mutex_init(&priv->lock);
> >>  
> >> -	ret = stm32_setup_iio_triggers(priv);
> >> +	ret = stm32_register_iio_triggers(priv);
> >>  	if (ret)
> >>  		return ret;
> >>  
> >> @@ -762,6 +796,25 @@ static int stm32_timer_trigger_probe(struct platform_device *pdev)
> >>  	return 0;
> >>  }
> >>  
> >> +static int stm32_timer_trigger_remove(struct platform_device *pdev)
> >> +{
> >> +	struct stm32_timer_trigger *priv = platform_get_drvdata(pdev);
> >> +	u32 val;
> >> +
> >> +	/* Unregister triggers before everything can be safely turned off */
> >> +	stm32_unregister_iio_triggers(priv);
> >> +
> >> +	/* Check if nobody else use the timer, then disable it */
> >> +	regmap_read(priv->regmap, TIM_CCER, &val);
> >> +	if (!(val & TIM_CCER_CCXE))
> >> +		regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN, 0);
> >> +
> >> +	if (priv->clk_enabled)
> >> +		clk_disable(priv->clk);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >>  static const struct stm32_timer_trigger_cfg stm32_timer_trg_cfg = {
> >>  	.valids_table = valids_table,
> >>  	.num_valids_table = ARRAY_SIZE(valids_table),
> >> @@ -786,6 +839,7 @@ MODULE_DEVICE_TABLE(of, stm32_trig_of_match);
> >>  
> >>  static struct platform_driver stm32_timer_trigger_driver = {
> >>  	.probe = stm32_timer_trigger_probe,
> >> +	.remove = stm32_timer_trigger_remove,
> >>  	.driver = {
> >>  		.name = "stm32-timer-trigger",
> >>  		.of_match_table = stm32_trig_of_match,  
> >   

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