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: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index e9faeaf..519ecfa 100644 (file)
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -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));
@@ -552,8 +559,9 @@ static irqreturn_t edge_irq_thread(int irq, void *p)
        }
        line->timestamp_ns = 0;
 
-       if (line->eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING |
-                            GPIO_V2_LINE_FLAG_EDGE_FALLING)) {
+       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);
 
                if (level)
@@ -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;
        }