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Message-ID: <CAMRc=MeoeOgZaz6xT+ScVjOemVovrEHvQDBvqsN1pD9U3haE_A@mail.gmail.com>
Date: Thu, 14 Dec 2023 15:29:28 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Kent Gibson <warthog618@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
linus.walleij@...aro.org, andy@...nel.org
Subject: Re: [PATCH v2 2/5] gpiolib: cdev: relocate debounce_period_us from
struct gpio_desc
On Thu, Dec 14, 2023 at 10:58 AM Kent Gibson <warthog618@...il.com> wrote:
>
> Store the debounce period for a requested line locally, rather than in
> the debounce_period_us field in the gpiolib struct gpio_desc.
>
> Add a global tree of lines containing supplemental line information
> to make the debounce period available to be reported by the
> GPIO_V2_GET_LINEINFO_IOCTL and the line change notifier.
>
> Signed-off-by: Kent Gibson <warthog618@...il.com>
> ---
> drivers/gpio/gpiolib-cdev.c | 167 +++++++++++++++++++++++++++++++-----
> 1 file changed, 145 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index d03698812f61..7da3b3706547 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -21,6 +21,7 @@
> #include <linux/mutex.h>
> #include <linux/pinctrl/consumer.h>
> #include <linux/poll.h>
> +#include <linux/rbtree.h>
> #include <linux/seq_file.h>
> #include <linux/spinlock.h>
> #include <linux/timekeeping.h>
> @@ -461,6 +462,7 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
>
> /**
> * struct line - contains the state of a requested line
> + * @node: to store the object in supinfo if supplemental
> * @desc: the GPIO descriptor for this line.
> * @req: the corresponding line request
> * @irq: the interrupt triggered in response to events on this GPIO
> @@ -473,6 +475,7 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
> * @line_seqno: the seqno for the current edge event in the sequence of
> * events for this line.
> * @work: the worker that implements software debouncing
> + * @debounce_period_us: the debounce period in microseconds
> * @sw_debounced: flag indicating if the software debouncer is active
> * @level: the current debounced physical level of the line
> * @hdesc: the Hardware Timestamp Engine (HTE) descriptor
> @@ -481,6 +484,7 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
> * @last_seqno: the last sequence number before debounce period expires
> */
> struct line {
> + struct rb_node node;
> struct gpio_desc *desc;
> /*
> * -- edge detector specific fields --
> @@ -514,6 +518,15 @@ struct line {
> * -- debouncer specific fields --
> */
> struct delayed_work work;
> + /*
> + * debounce_period_us is accessed by debounce_irq_handler() and
> + * process_hw_ts() which are disabled when modified by
> + * debounce_setup(), edge_detector_setup() or edge_detector_stop()
> + * or can live with a stale version when updated by
> + * edge_detector_update().
> + * The modifying functions are themselves mutually exclusive.
> + */
> + unsigned int debounce_period_us;
> /*
> * sw_debounce is accessed by linereq_set_config(), which is the
> * only setter, and linereq_get_values(), which can live with a
> @@ -546,6 +559,19 @@ struct line {
> #endif /* CONFIG_HTE */
> };
>
> +/*
> + * Used to populate gpio_v2_line_info with cdev specific fields not contained
> + * in the struct gpio_desc.
> + * A line is determined to contain supplemental information by
> + * line_is_supplemental().
> + */
> +static struct {
> + /* a rbtree of the struct lines containing the supplemental info */
> + struct rb_root tree;
> + /* covers tree */
> + spinlock_t lock;
Looks like this is never taken from atomic context? Can this be a mutex instead?
> +} supinfo;
> +
> /**
> * struct linereq - contains the state of a userspace line request
> * @gdev: the GPIO device the line request pertains to
> @@ -575,6 +601,100 @@ struct linereq {
> struct line lines[] __counted_by(num_lines);
> };
>
> +static void supinfo_init(void)
> +{
> + supinfo.tree = RB_ROOT;
> + spin_lock_init(&supinfo.lock);
> +}
> +
> +static void supinfo_insert(struct line *line)
> +{
> + struct rb_node **new = &(supinfo.tree.rb_node), *parent = NULL;
> + struct line *entry;
> +
> + scoped_guard(spinlock, &supinfo.lock) {
> + while (*new) {
> + entry = container_of(*new, struct line, node);
> +
> + parent = *new;
> + if (line->desc < entry->desc) {
> + new = &((*new)->rb_left);
> + } else if (line->desc > entry->desc) {
> + new = &((*new)->rb_right);
> + } else {
> + /* this should never happen */
> + WARN(1, "duplicate line inserted");
> + return;
> + }
> + }
> +
> + rb_link_node(&line->node, parent, new);
> + rb_insert_color(&line->node, &supinfo.tree);
> + }
> +}
> +
> +static void supinfo_erase(struct line *line)
> +{
> + scoped_guard(spinlock, &supinfo.lock)
> + rb_erase(&line->node, &supinfo.tree);
> +}
> +
> +static struct line *supinfo_find(struct gpio_desc *desc)
> +{
> + struct rb_node *node = supinfo.tree.rb_node;
> + struct line *line;
> +
> + while (node) {
> + line = container_of(node, struct line, node);
> + if (desc < line->desc)
> + node = node->rb_left;
> + else if (desc > line->desc)
> + node = node->rb_right;
> + else
> + return line;
> + }
> + return NULL;
> +}
> +
> +static void supinfo_to_lineinfo(struct gpio_desc *desc,
> + struct gpio_v2_line_info *info)
> +{
> + struct gpio_v2_line_attribute *attr;
> + struct line *line;
> +
> + scoped_guard(spinlock, &supinfo.lock) {
> + line = supinfo_find(desc);
> + if (line) {
> + attr = &info->attrs[info->num_attrs];
> + attr->id = GPIO_V2_LINE_ATTR_ID_DEBOUNCE;
> + attr->debounce_period_us =
> + READ_ONCE(line->debounce_period_us);
> + info->num_attrs++;
> + }
> + }
> +}
> +
> +static inline bool line_is_supplemental(struct line *line)
I would call this function line_has_suppinfo().
> +{
> + return READ_ONCE(line->debounce_period_us);
> +}
> +
> +static void line_set_debounce_period(struct line *line,
> + unsigned int debounce_period_us)
> +{
> + bool was_suppl = line_is_supplemental(line);
This logic could use some comments, it took me a while to figure out
what it's doing.
> +
> + WRITE_ONCE(line->debounce_period_us, debounce_period_us);
> +
> + if (line_is_supplemental(line) == was_suppl)
> + return;
> +
> + if (was_suppl)
> + supinfo_erase(line);
> + else
> + supinfo_insert(line);
> +}
> +
> #define GPIO_V2_LINE_BIAS_FLAGS \
> (GPIO_V2_LINE_FLAG_BIAS_PULL_UP | \
> GPIO_V2_LINE_FLAG_BIAS_PULL_DOWN | \
> @@ -723,7 +843,7 @@ static enum hte_return process_hw_ts(struct hte_ts_data *ts, void *p)
> line->total_discard_seq++;
> line->last_seqno = ts->seq;
> mod_delayed_work(system_wq, &line->work,
> - usecs_to_jiffies(READ_ONCE(line->desc->debounce_period_us)));
> + usecs_to_jiffies(READ_ONCE(line->debounce_period_us)));
> } else {
> if (unlikely(ts->seq < line->line_seqno))
> return HTE_CB_HANDLED;
> @@ -864,7 +984,7 @@ static irqreturn_t debounce_irq_handler(int irq, void *p)
> struct line *line = p;
>
> mod_delayed_work(system_wq, &line->work,
> - usecs_to_jiffies(READ_ONCE(line->desc->debounce_period_us)));
> + usecs_to_jiffies(READ_ONCE(line->debounce_period_us)));
>
> return IRQ_HANDLED;
> }
> @@ -946,7 +1066,7 @@ static int debounce_setup(struct line *line, unsigned int debounce_period_us)
> /* try hardware */
> ret = gpiod_set_debounce(line->desc, debounce_period_us);
> if (!ret) {
> - WRITE_ONCE(line->desc->debounce_period_us, debounce_period_us);
> + line_set_debounce_period(line, debounce_period_us);
> return ret;
> }
> if (ret != -ENOTSUPP)
> @@ -1025,8 +1145,7 @@ static void edge_detector_stop(struct line *line)
> cancel_delayed_work_sync(&line->work);
> WRITE_ONCE(line->sw_debounced, 0);
> WRITE_ONCE(line->edflags, 0);
> - if (line->desc)
> - WRITE_ONCE(line->desc->debounce_period_us, 0);
> + line_set_debounce_period(line, 0);
> /* do not change line->level - see comment in debounced_value() */
> }
>
> @@ -1051,7 +1170,7 @@ static int edge_detector_setup(struct line *line,
> ret = debounce_setup(line, debounce_period_us);
> if (ret)
> return ret;
> - WRITE_ONCE(line->desc->debounce_period_us, debounce_period_us);
> + line_set_debounce_period(line, debounce_period_us);
> }
>
> /* detection disabled or sw debouncer will provide edge detection */
> @@ -1093,12 +1212,12 @@ static int edge_detector_update(struct line *line,
> gpio_v2_line_config_debounce_period(lc, line_idx);
>
> if ((active_edflags == edflags) &&
> - (READ_ONCE(line->desc->debounce_period_us) == debounce_period_us))
> + (READ_ONCE(line->debounce_period_us) == debounce_period_us))
> return 0;
>
> /* sw debounced and still will be...*/
> if (debounce_period_us && READ_ONCE(line->sw_debounced)) {
> - WRITE_ONCE(line->desc->debounce_period_us, debounce_period_us);
> + line_set_debounce_period(line, debounce_period_us);
> return 0;
> }
>
> @@ -1561,6 +1680,7 @@ static ssize_t linereq_read(struct file *file, char __user *buf,
>
> static void linereq_free(struct linereq *lr)
> {
> + struct line *line;
> unsigned int i;
>
> if (lr->device_unregistered_nb.notifier_call)
> @@ -1568,10 +1688,14 @@ static void linereq_free(struct linereq *lr)
> &lr->device_unregistered_nb);
>
> for (i = 0; i < lr->num_lines; i++) {
> - if (lr->lines[i].desc) {
> - edge_detector_stop(&lr->lines[i]);
> - gpiod_free(lr->lines[i].desc);
> - }
> + line = &lr->lines[i];
> + if (!line->desc)
> + continue;
> +
> + edge_detector_stop(line);
> + if (line_is_supplemental(line))
> + supinfo_erase(line);
> + gpiod_free(line->desc);
> }
> kfifo_free(&lr->events);
> kfree(lr->label);
> @@ -2256,8 +2380,6 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
> struct gpio_chip *gc = desc->gdev->chip;
> bool ok_for_pinctrl;
> unsigned long flags;
> - u32 debounce_period_us;
> - unsigned int num_attrs = 0;
>
> memset(info, 0, sizeof(*info));
> info->offset = gpio_chip_hwgpio(desc);
> @@ -2323,14 +2445,6 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
> else if (test_bit(FLAG_EVENT_CLOCK_HTE, &desc->flags))
> info->flags |= GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE;
>
> - debounce_period_us = READ_ONCE(desc->debounce_period_us);
> - if (debounce_period_us) {
> - info->attrs[num_attrs].id = GPIO_V2_LINE_ATTR_ID_DEBOUNCE;
> - info->attrs[num_attrs].debounce_period_us = debounce_period_us;
> - num_attrs++;
> - }
> - info->num_attrs = num_attrs;
> -
> spin_unlock_irqrestore(&gpio_lock, flags);
> }
>
> @@ -2437,6 +2551,7 @@ static int lineinfo_get(struct gpio_chardev_data *cdev, void __user *ip,
> return -EBUSY;
> }
> gpio_desc_to_lineinfo(desc, &lineinfo);
> + supinfo_to_lineinfo(desc, &lineinfo);
>
> if (copy_to_user(ip, &lineinfo, sizeof(lineinfo))) {
> if (watch)
> @@ -2527,6 +2642,7 @@ static int lineinfo_changed_notify(struct notifier_block *nb,
> chg.event_type = action;
> chg.timestamp_ns = ktime_get_ns();
> gpio_desc_to_lineinfo(desc, &chg.info);
> + supinfo_to_lineinfo(desc, &chg.info);
>
> ret = kfifo_in_spinlocked(&cdev->events, &chg, 1, &cdev->wait.lock);
> if (ret)
> @@ -2786,3 +2902,10 @@ void gpiolib_cdev_unregister(struct gpio_device *gdev)
> cdev_device_del(&gdev->chrdev, &gdev->dev);
> blocking_notifier_call_chain(&gdev->device_notifier, 0, NULL);
> }
> +
> +static int __init gpiolib_cdev_init(void)
> +{
> + supinfo_init();
> + return 0;
> +}
> +postcore_initcall(gpiolib_cdev_init);
> --
> 2.39.2
>
Bart
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