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

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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