gpio: userspace ABI for reading/writing GPIO lines

This adds a userspace ABI for reading and writing GPIO lines.
The mechanism returns an anonymous file handle to a request
to read/write n offsets from a gpiochip. This file handle
in turn accepts two ioctl()s: one that reads and one that
writes values to the selected lines.

- Handles can be requested as input/output, active low,
  open drain, open source, however when you issue a request
  for n lines with GPIO_GET_LINEHANDLE_IOCTL, they must all
  have the same flags, i.e. all inputs or all outputs, all
  open drain etc. If a granular control of the flags for
  each line is desired, they need to be requested
  individually, not in a batch.

- The GPIOHANDLE_GET_LINE_VALUES_IOCTL read ioctl() can be
  issued also to output lines to verify that the hardware
  is in the expected state.

- It reads and writes up to GPIOHANDLES_MAX lines at once,
  utilizing the .set_multiple() call in the driver if
  possible, making the call efficient if several lines
  can be written with a single register update.

The limitation of GPIOHANDLES_MAX to 64 lines is done under
the assumption that we may expect hardware that can issue a
transaction updating 64 bits at an instant but unlikely
anything larger than that.

ChangeLog v2->v3:
- Use gpiod_get_value_cansleep() so we support also slowpath
  GPIO drivers.
- Fix up the UAPI docs kerneldoc.
- Allocate the anonymous fd last, so that the release
  function don't get called until that point of something
  fails. After this point, skip the errorpath.
ChangeLog v1->v2:
- Handle ioctl_compat() properly based on a similar patch
  to the other ioctl() handling code.
- Use _IOWR() as we pass pointers both in and out of the
  ioctl()
- Use kmalloc() and kfree() for the linehandled, do not
  try to be fancy with devm_* it doesn't work the way I
  thought.
- Fix const-correctness on the linehandle name field.

Acked-by: Michael Welling <mwelling@ieee.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 58 insertions, 3 deletions

diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
index d0a3cac72250..21905531dcf4 100644
--- a/include/uapi/linux/gpio.h
+++ b/include/uapi/linux/gpio.h
@@ -1,7 +1,7 @@
 /*
  * <linux/gpio.h> - userspace ABI for the GPIO character devices
  *
- * Copyright (C) 2015 Linus Walleij
+ * Copyright (C) 2016 Linus Walleij
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 as published by
@@ -26,8 +26,8 @@ struct gpiochip_info {
 	__u32 lines;
 };
 
-/* Line is in use by the kernel */
-#define GPIOLINE_FLAG_KERNEL		(1UL << 0)
+/* Informational flags */
+#define GPIOLINE_FLAG_KERNEL		(1UL << 0) /* Line used by the kernel */
 #define GPIOLINE_FLAG_IS_OUT		(1UL << 1)
 #define GPIOLINE_FLAG_ACTIVE_LOW	(1UL << 2)
 #define GPIOLINE_FLAG_OPEN_DRAIN	(1UL << 3)
@@ -52,7 +52,62 @@ struct gpioline_info {
 	char consumer[32];
 };
 
+/* Maximum number of requested handles */
+#define GPIOHANDLES_MAX 64
+
+/* Request flags */
+#define GPIOHANDLE_REQUEST_INPUT	(1UL << 0)
+#define GPIOHANDLE_REQUEST_OUTPUT	(1UL << 1)
+#define GPIOHANDLE_REQUEST_ACTIVE_LOW	(1UL << 2)
+#define GPIOHANDLE_REQUEST_OPEN_DRAIN	(1UL << 3)
+#define GPIOHANDLE_REQUEST_OPEN_SOURCE	(1UL << 4)
+
+/**
+ * struct gpiohandle_request - Information about a GPIO handle request
+ * @lineoffsets: an array desired lines, specified by offset index for the
+ * associated GPIO device
+ * @flags: desired flags for the desired GPIO lines, such as
+ * GPIOHANDLE_REQUEST_OUTPUT, GPIOHANDLE_REQUEST_ACTIVE_LOW etc, OR:ed
+ * together. Note that even if multiple lines are requested, the same flags
+ * must be applicable to all of them, if you want lines with individual
+ * flags set, request them one by one. It is possible to select
+ * a batch of input or output lines, but they must all have the same
+ * characteristics, i.e. all inputs or all outputs, all active low etc
+ * @default_values: if the GPIOHANDLE_REQUEST_OUTPUT is set for a requested
+ * line, this specifies the default output value, should be 0 (low) or
+ * 1 (high), anything else than 0 or 1 will be interpreted as 1 (high)
+ * @consumer_label: a desired consumer label for the selected GPIO line(s)
+ * such as "my-bitbanged-relay"
+ * @lines: number of lines requested in this request, i.e. the number of
+ * valid fields in the above arrays, set to 1 to request a single line
+ * @fd: if successful this field will contain a valid anonymous file handle
+ * after a GPIO_GET_LINEHANDLE_IOCTL operation, zero or negative value
+ * means error
+ */
+struct gpiohandle_request {
+	__u32 lineoffsets[GPIOHANDLES_MAX];
+	__u32 flags;
+	__u8 default_values[GPIOHANDLES_MAX];
+	char consumer_label[32];
+	__u32 lines;
+	int fd;
+};
+
 #define GPIO_GET_CHIPINFO_IOCTL _IOR(0xB4, 0x01, struct gpiochip_info)
 #define GPIO_GET_LINEINFO_IOCTL _IOWR(0xB4, 0x02, struct gpioline_info)
+#define GPIO_GET_LINEHANDLE_IOCTL _IOWR(0xB4, 0x03, struct gpiohandle_request)
+
+/**
+ * struct gpiohandle_data - Information of values on a GPIO handle
+ * @values: when getting the state of lines this contains the current
+ * state of a line, when setting the state of lines these should contain
+ * the desired target state
+ */
+struct gpiohandle_data {
+	__u8 values[GPIOHANDLES_MAX];
+};
+
+#define GPIOHANDLE_GET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x08, struct gpiohandle_data)
+#define GPIOHANDLE_SET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x09, struct gpiohandle_data)
 
 #endif /* _UAPI_GPIO_H_ */