gpiolib: Identify arrays matching GPIO hardware

Certain GPIO array lookup results may map directly to GPIO pins of a
single GPIO chip in hardware order.  If that condition is recognized
and handled efficiently, significant performance gain of get/set array
functions may be possible.

While processing a request for an array of GPIO descriptors, identify
those which represent corresponding pins of a single GPIO chip.  Skip
over pins which require open source or open drain special processing.
Moreover, identify pins which require inversion.  Pass a pointer to
that information with the array to the caller so it can benefit from
enhanced performance as soon as get/set array functions can accept and
make efficient use of it.

Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/consumer.h

@@ -17,11 +17,20 @@ struct device;
  */
 struct gpio_desc;
 
+/**
+ * Opaque descriptor for a structure of GPIO array attributes.  This structure
+ * is attached to struct gpiod_descs obtained from gpiod_get_array() and can be
+ * passed back to get/set array functions in order to activate fast processing
+ * path if applicable.
+ */
+struct gpio_array;
+
 /**
  * Struct containing an array of descriptors that can be obtained using
  * gpiod_get_array().
  */
 struct gpio_descs {
+	struct gpio_array *info;
 	unsigned int ndescs;
 	struct gpio_desc *desc[];
 };