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Subject: Re: [PATCH v2] iio: trigger: stm32-timer: enable clock when in master
 mode
To:     Jonathan Cameron <jic23@kernel.org>
CC:     <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <mcoquelin.stm32@gmail.com>,
        <benjamin.gaignard@st.com>, <alexandre.torgue@st.com>,
        <olivier.moysan@st.com>, <linux-iio@vger.kernel.org>,
        <lars@metafoo.de>, <knaack.h@gmx.de>, <pmeerw@pmeerw.net>,
        <linux-stm32@st-md-mailman.stormreply.com>
References: <1581093031-9871-1-git-send-email-fabrice.gasnier@st.com>
 <20200214142035.576e11e1@archlinux>
From:   Fabrice Gasnier <fabrice.gasnier@st.com>
Message-ID: <3a9dfc05-f6c3-a283-5791-5d9b72bb44f7@st.com>
Date:   Fri, 14 Feb 2020 15:50:57 +0100
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On 2/14/20 3:20 PM, Jonathan Cameron wrote:
> On Fri, 7 Feb 2020 17:30:31 +0100
> Fabrice Gasnier <fabrice.gasnier@st.com> 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 <fabrice.gasnier@st.com>
> 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.

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,
>