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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>
 <3a9dfc05-f6c3-a283-5791-5d9b72bb44f7@st.com>
 <20200214151408.570c1658@archlinux>
From:   Fabrice Gasnier <fabrice.gasnier@st.com>
Message-ID: <bc6cc13a-5ac5-f9cc-5b22-55ca1cfc9bd9@st.com>
Date:   Fri, 14 Feb 2020 17:18:35 +0100
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On 2/14/20 4:14 PM, Jonathan Cameron wrote:
> On Fri, 14 Feb 2020 15:50:57 +0100
> Fabrice Gasnier <fabrice.gasnier@st.com> wrote:
> 
>> 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.
> 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!

Yes, I'll do this shortly ;-)

Thanks,
Fabrice
> 
> 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,  
>>>   
>