Commit 3ffb7c45 authored by Kent Gibson's avatar Kent Gibson Committed by Bartosz Golaszewski
Browse files

gpiolib: cdev: document that line eflags are shared 



The line.eflags field is shared so document this fact and highlight it
throughout using READ_ONCE() and WRITE_ONCE() accessors.

Also use a local copy of the eflags in edge_irq_thread() to ensure
consistent control flow even if eflags changes.  This is only a defensive
measure as edge_irq_thread() is currently disabled when the eflags are
changed.

Signed-off-by: default avatarKent Gibson <warthog618@gmail.com>
Signed-off-by: default avatarBartosz Golaszewski <bgolaszewski@baylibre.com>
parent 7b58696d

drivers/gpio/gpiolib-cdev.c

+21 −11
Original line number Diff line number Diff line
@@ -428,6 +428,12 @@ struct line { 
	 */

	struct linereq *req;

	unsigned int irq;

	/*

	 * eflags is set by edge_detector_setup(), edge_detector_stop() and

	 * edge_detector_update(), which are themselves mutually exclusive,

	 * and is accessed by edge_irq_thread() and debounce_work_func(),

	 * which can both live with a slightly stale value.

	 */

	u64 eflags;

	/*

	 * timestamp_ns and req_seqno are accessed only by
@@ -534,6 +540,7 @@ static irqreturn_t edge_irq_thread(int irq, void *p) 
	struct line *line = p;

	struct linereq *lr = line->req;

	struct gpio_v2_line_event le;

	u64 eflags;



	/* Do not leak kernel stack to userspace */

	memset(&le, 0, sizeof(le));
@@ -552,7 +559,8 @@ static irqreturn_t edge_irq_thread(int irq, void *p) 
	}

	line->timestamp_ns = 0;



	if (line->eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING |

	eflags = READ_ONCE(line->eflags);

	if (eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING |

		       GPIO_V2_LINE_FLAG_EDGE_FALLING)) {

		int level = gpiod_get_value_cansleep(line->desc);
@@ -562,10 +570,10 @@ static irqreturn_t edge_irq_thread(int irq, void *p) 
		else

			/* Emit high-to-low event */

			le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;

	} else if (line->eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) {

	} else if (eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) {

		/* Emit low-to-high event */

		le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;

	} else if (line->eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) {

	} else if (eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) {

		/* Emit high-to-low event */

		le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;

	} else {
@@ -634,6 +642,7 @@ static void debounce_work_func(struct work_struct *work) 
	struct line *line = container_of(work, struct line, work.work);

	struct linereq *lr;

	int level;

	u64 eflags;



	level = gpiod_get_raw_value_cansleep(line->desc);

	if (level < 0) {
@@ -647,7 +656,8 @@ static void debounce_work_func(struct work_struct *work) 
	WRITE_ONCE(line->level, level);



	/* -- edge detection -- */

	if (!line->eflags)

	eflags = READ_ONCE(line->eflags);

	if (!eflags)

		return;



	/* switch from physical level to logical - if they differ */
@@ -655,8 +665,8 @@ static void debounce_work_func(struct work_struct *work) 
		level = !level;



	/* ignore edges that are not being monitored */

	if (((line->eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) && !level) ||

	    ((line->eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) && level))

	if (((eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) && !level) ||

	    ((eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) && level))

		return;



	/* Do not leak kernel stack to userspace */
@@ -755,7 +765,7 @@ static void edge_detector_stop(struct line *line) 


	cancel_delayed_work_sync(&line->work);

	WRITE_ONCE(line->sw_debounced, 0);

	line->eflags = 0;

	WRITE_ONCE(line->eflags, 0);

	/* do not change line->level - see comment in debounced_value() */

}
@@ -774,7 +784,7 @@ static int edge_detector_setup(struct line *line, 
		if (ret)

			return ret;

	}

	line->eflags = eflags;

	WRITE_ONCE(line->eflags, eflags);

	if (gpio_v2_line_config_debounced(lc, line_idx)) {

		debounce_period_us = gpio_v2_line_config_debounce_period(lc, line_idx);

		ret = debounce_setup(line, debounce_period_us);
@@ -817,13 +827,13 @@ static int edge_detector_update(struct line *line, 
	unsigned int debounce_period_us =

		gpio_v2_line_config_debounce_period(lc, line_idx);



	if ((line->eflags == eflags) && !polarity_change &&

	if ((READ_ONCE(line->eflags) == eflags) && !polarity_change &&

	    (READ_ONCE(line->desc->debounce_period_us) == debounce_period_us))

		return 0;



	/* sw debounced and still will be...*/

	if (debounce_period_us && READ_ONCE(line->sw_debounced)) {

		line->eflags = eflags;

		WRITE_ONCE(line->eflags, eflags);

		WRITE_ONCE(line->desc->debounce_period_us, debounce_period_us);

		return 0;

	}

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