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gpiolib: cdev: document that line eflags are shared

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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: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
This commit is contained in:
Kent Gibson 2020-10-14 14:29:21 +08:00 committed by Bartosz Golaszewski
parent 7b58696d9a
commit 3ffb7c45d1
1 changed files with 21 additions and 11 deletions
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32
drivers/gpio/gpiolib-cdev.c
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@ -428,6 +428,12 @@ struct line {
*/ */
struct linereq *req; struct linereq *req;
unsigned int irq; 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; u64 eflags;
/* /*
* timestamp_ns and req_seqno are accessed only by * 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 line *line = p;
struct linereq *lr = line->req; struct linereq *lr = line->req;
struct gpio_v2_line_event le; struct gpio_v2_line_event le;
u64 eflags;
/* Do not leak kernel stack to userspace */ /* Do not leak kernel stack to userspace */
memset(&le, 0, sizeof(le)); memset(&le, 0, sizeof(le));
@ -552,8 +559,9 @@ static irqreturn_t edge_irq_thread(int irq, void *p)
} }
line->timestamp_ns = 0; line->timestamp_ns = 0;
if (line->eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING | eflags = READ_ONCE(line->eflags);
GPIO_V2_LINE_FLAG_EDGE_FALLING)) { if (eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING |
GPIO_V2_LINE_FLAG_EDGE_FALLING)) {
int level = gpiod_get_value_cansleep(line->desc); int level = gpiod_get_value_cansleep(line->desc);
if (level) if (level)
@ -562,10 +570,10 @@ static irqreturn_t edge_irq_thread(int irq, void *p)
else else
/* Emit high-to-low event */ /* Emit high-to-low event */
le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE; 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 */ /* Emit low-to-high event */
le.id = GPIO_V2_LINE_EVENT_RISING_EDGE; 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 */ /* Emit high-to-low event */
le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE; le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE;
} else { } 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 line *line = container_of(work, struct line, work.work);
struct linereq *lr; struct linereq *lr;
int level; int level;
u64 eflags;
level = gpiod_get_raw_value_cansleep(line->desc); level = gpiod_get_raw_value_cansleep(line->desc);
if (level < 0) { if (level < 0) {
@ -647,7 +656,8 @@ static void debounce_work_func(struct work_struct *work)
WRITE_ONCE(line->level, level); WRITE_ONCE(line->level, level);
/* -- edge detection -- */ /* -- edge detection -- */
if (!line->eflags) eflags = READ_ONCE(line->eflags);
if (!eflags)
return; return;
/* switch from physical level to logical - if they differ */ /* switch from physical level to logical - if they differ */
@ -655,8 +665,8 @@ static void debounce_work_func(struct work_struct *work)
level = !level; level = !level;
/* ignore edges that are not being monitored */ /* ignore edges that are not being monitored */
if (((line->eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) && !level) || if (((eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) && !level) ||
((line->eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) && level)) ((eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) && level))
return; return;
/* Do not leak kernel stack to userspace */ /* 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); cancel_delayed_work_sync(&line->work);
WRITE_ONCE(line->sw_debounced, 0); WRITE_ONCE(line->sw_debounced, 0);
line->eflags = 0; WRITE_ONCE(line->eflags, 0);
/* do not change line->level - see comment in debounced_value() */ /* do not change line->level - see comment in debounced_value() */
} }
@ -774,7 +784,7 @@ static int edge_detector_setup(struct line *line,
if (ret) if (ret)
return ret; return ret;
} }
line->eflags = eflags; WRITE_ONCE(line->eflags, eflags);
if (gpio_v2_line_config_debounced(lc, line_idx)) { if (gpio_v2_line_config_debounced(lc, line_idx)) {
debounce_period_us = gpio_v2_line_config_debounce_period(lc, line_idx); debounce_period_us = gpio_v2_line_config_debounce_period(lc, line_idx);
ret = debounce_setup(line, debounce_period_us); ret = debounce_setup(line, debounce_period_us);
@ -817,13 +827,13 @@ static int edge_detector_update(struct line *line,
unsigned int debounce_period_us = unsigned int debounce_period_us =
gpio_v2_line_config_debounce_period(lc, line_idx); 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)) (READ_ONCE(line->desc->debounce_period_us) == debounce_period_us))
return 0; return 0;
/* sw debounced and still will be...*/ /* sw debounced and still will be...*/
if (debounce_period_us && READ_ONCE(line->sw_debounced)) { 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); WRITE_ONCE(line->desc->debounce_period_us, debounce_period_us);
return 0; return 0;
} }