Provide userland notification of gpio pin changes ("userland gpio interrupts").

This is an import of the Google Summer of Code 2018 project completed by
Christian Kramer (and, sadly, ignored by us for two years now).  The goals
stated for that project were:

    FreeBSD already has support for interrupts implemented in the GPIO
    controller drivers of several SoCs, but there are no interfaces to take
    advantage of them out of user space yet. The goal of this work is to
    implement such an interface by providing descriptors which integrate
    with the common I/O system calls and multiplexing mechanisms.

The initial imported code supports the following functionality:

 -  A kernel driver that provides an interface to the user space; the
    existing gpioc(4) driver was enhanced with this functionality.
 -  Implement support for the most common I/O system calls / multiplexing
    mechanisms:
     -  read() Places the pin number on which the interrupt occurred in the
        buffer. Blocking and non-blocking behaviour supported.
     -	poll()/select()
     -	kqueue()
     -	signal driven I/O. Posting SIGIO when the O_ASYNC was set.
 -  Many-to-many relationship between pins and file descriptors.
     -  A file descriptor can monitor several GPIO pins.
     -  A GPIO pin can be monitored by multiple file descriptors.
 -  Integration with gpioctl and libgpio.

I added some fixes (mostly to locking) and feature enhancements on top of
the original gsoc code.  The feature ehancements allow the user to choose
between detailed and summary event reporting.  Detailed reporting provides
a record describing each pin change event.  Summary reporting provides the
time of the first and last change of each pin, and a count of how many times
it changed state since the last read(2) call.  Another enhancement allows
the recording of multiple state change events on multiple pins between each
call to read(2) (the original code would track only a single event at a time).

The phabricator review for these changes timed out without approval, but I
cite it below anyway, because the review contains a series of diffs that
show how I evolved the code from its original state in Christian's github
repo for the gsoc project to what is being commited here.  (In effect,
the phab review extends the VC history back to the original code.)

Submitted by:	Christian Kramer
Obtained from:	https://github.com/ckraemer/freebsd/tree/gsoc2018
Differential Revision:	https://reviews.freebsd.org/D27398

1 files changed, 60 insertions, 4 deletions

diff --git a/sys/sys/gpio.h b/sys/sys/gpio.h
index 2505269de64d..50b9b9dbb0e5 100644
--- a/sys/sys/gpio.h
+++ b/sys/sys/gpio.h
@@ -53,6 +53,9 @@
 #define __GPIO_H__
 
 #include <sys/ioccom.h>
+#ifndef _KERNEL
+#include <stdbool.h>
+#endif
 
 /* GPIO pin states */
 #define GPIO_PIN_LOW		0x00	/* low level (logical 0) */
@@ -81,9 +84,11 @@
 #define GPIO_INTR_EDGE_RISING	0x00040000	/* edge trigger, rising */
 #define GPIO_INTR_EDGE_FALLING	0x00080000	/* edge trigger, falling */
 #define GPIO_INTR_EDGE_BOTH	0x00100000	/* edge trigger, both */
-#define GPIO_INTR_MASK		(GPIO_INTR_LEVEL_LOW | GPIO_INTR_LEVEL_HIGH | \
-				GPIO_INTR_EDGE_RISING |			      \
-				GPIO_INTR_EDGE_FALLING | GPIO_INTR_EDGE_BOTH)
+#define GPIO_INTR_ATTACHED	0x00200000	/* interrupt attached to file */
+#define GPIO_INTR_MASK		(GPIO_INTR_LEVEL_LOW | GPIO_INTR_LEVEL_HIGH |  \
+				GPIO_INTR_EDGE_RISING |			       \
+				GPIO_INTR_EDGE_FALLING | GPIO_INTR_EDGE_BOTH | \
+				GPIO_INTR_ATTACHED)
 
 struct gpio_pin {
 	uint32_t gp_pin;			/* pin number */
@@ -99,6 +104,53 @@ struct gpio_req {
 };
 
 /*
+ * Reporting gpio pin-change per-event details to userland.
+ *
+ * When configured for detail reporting, each call to read(2) will return one or
+ * more of these structures (or will return EWOULDBLOCK in non-blocking IO mode
+ * when there are no new events to report).
+ */
+struct gpio_event_detail {
+	sbintime_t	gp_time;	/* Time of event */
+	uint16_t	gp_pin;		/* Pin number */
+	bool		gp_pinstate;	/* Pin state at time of event */
+};
+
+/*
+ * Reporting gpio pin-change summary data to userland.
+ *
+ * When configured for summary reporting, each call to read(2) will return one
+ * or more of these structures (or will return EWOULDBLOCK in non-blocking IO
+ * mode when there are no new events to report).
+ */
+struct gpio_event_summary {
+	sbintime_t	gp_first_time;	/* Time of first event */
+	sbintime_t	gp_last_time;	/* Time of last event */
+	uint16_t	gp_pin;		/* Pin number */
+	uint16_t	gp_count;	/* Event count */
+	bool		gp_first_state;	/* Pin state at first event */
+	bool		gp_last_state;	/* Pin state at last event */
+};
+
+/*
+ * Configuring event reporting to userland.
+ *
+ * The default is to deliver gpio_event_detail reporting, with a default fifo
+ * size of 2 * number of pins belonging to the gpioc device instance.  To change
+ * it, you must use the GPIOCONFIGEVENTS ioctl before using GPIOSETCONFIG to
+ * configure reporting interrupt events on any pins.  This config is tracked on
+ * a per-open-descriptor basis.
+ */
+enum {
+	GPIO_EVENT_REPORT_DETAIL,	/* Report detail on each event */
+	GPIO_EVENT_REPORT_SUMMARY,	/* Report summary of events */
+};
+struct gpio_event_config {
+	uint32_t	gp_report_type; /* Detail or summary reporting */
+	uint32_t	gp_fifo_size;	/* FIFO size (used for detail only) */
+};
+
+/*
  * gpio_access_32 / GPIOACCESS32
  *
  * Simultaneously read and/or change up to 32 adjacent pins.
@@ -147,7 +199,7 @@ struct gpio_access_32 {
  * contains any GPIO_PIN_OUTPUT flags, the driver will manipulate the hardware
  * such that all output pins become driven with the proper initial values
  * simultaneously if it can.  The elements in the array map to pins in the same
- * way that bits are mapped by pin_acces_32(), and the same restrictions may
+ * way that bits are mapped by pin_access_32(), and the same restrictions may
  * apply.  For example, to configure pins 2 and 3 it may be necessary to set
  * first_pin to zero and only populate pin_flags[2] and pin_flags[3].  If a
  * given array entry doesn't contain GPIO_PIN_INPUT or GPIO_PIN_OUTPUT then no
@@ -156,6 +208,9 @@ struct gpio_access_32 {
  * Some devices may limit the value of first_pin to 0, or to multiples of 16 or
  * 32 or some other hardware-specific number.  Invalid values in first_pin or
  * num_pins result in an error return with errno set to EINVAL.
+ *
+ * You cannot configure interrupts (userland pin-change notifications) with
+ * this function; each interrupt pin must be individually configured.
  */
 struct gpio_config_32 {
 	uint32_t first_pin;
@@ -175,5 +230,6 @@ struct gpio_config_32 {
 #define	GPIOSETNAME		_IOW('G', 6, struct gpio_pin)
 #define	GPIOACCESS32		_IOWR('G', 7, struct gpio_access_32)
 #define	GPIOCONFIG32		_IOW('G', 8, struct gpio_config_32)
+#define	GPIOCONFIGEVENTS	_IOW('G', 9, struct gpio_event_config)
 
 #endif /* __GPIO_H__ */