These changes are the raw update to linux-4.4.6-rt14. Kernel sources

[kvmfornfv.git] / kernel / Documentation / gpio / consumer.txt

diff --git a/kernel/Documentation/gpio/consumer.txt b/kernel/Documentation/gpio/consumer.txt
index c21c131..e000502 100644 (file)
--- a/kernel/Documentation/gpio/consumer.txt
+++ b/kernel/Documentation/gpio/consumer.txt
@@ -39,6 +39,9 @@ device that displays digits), an additional index argument can be specified:
                                          const char *con_id, unsigned int idx,
                                          enum gpiod_flags flags)
 
+For a more detailed description of the con_id parameter in the DeviceTree case
+see Documentation/gpio/board.txt
+
 The flags parameter is used to optionally specify a direction and initial value
 for the GPIO. Values can be:
 
@@ -237,22 +240,55 @@ Note that these functions should only be used with great moderation ; a driver
 should not have to care about the physical line level.
 
 
+The active-low property
+-----------------------
+
+As a driver should not have to care about the physical line level, all of the
+gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
+the *logical* value. With this they take the active-low property into account.
+This means that they check whether the GPIO is configured to be active-low,
+and if so, they manipulate the passed value before the physical line level is
+driven.
+
+With this, all the gpiod_set_(array)_value_xxx() functions interpret the
+parameter "value" as "active" ("1") or "inactive" ("0"). The physical line
+level will be driven accordingly.
+
+As an example, if the active-low property for a dedicated GPIO is set, and the
+gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level
+will be driven low.
+
+To summarize:
+
+Function (example)               active-low proporty  physical line
+gpiod_set_raw_value(desc, 0);        don't care           low
+gpiod_set_raw_value(desc, 1);        don't care           high
+gpiod_set_value(desc, 0);       default (active-high)     low
+gpiod_set_value(desc, 1);       default (active-high)     high
+gpiod_set_value(desc, 0);             active-low          high
+gpiod_set_value(desc, 1);             active-low          low
+
+Please note again that the set_raw/get_raw functions should be avoided as much
+as possible, especially by drivers which should not care about the actual
+physical line level and worry about the logical value instead.
+
+
 Set multiple GPIO outputs with a single function call
 -----------------------------------------------------
 The following functions set the output values of an array of GPIOs:
 
-       void gpiod_set_array(unsigned int array_size,
-                            struct gpio_desc **desc_array,
-                            int *value_array)
-       void gpiod_set_raw_array(unsigned int array_size,
-                                struct gpio_desc **desc_array,
-                                int *value_array)
-       void gpiod_set_array_cansleep(unsigned int array_size,
-                                     struct gpio_desc **desc_array,
-                                     int *value_array)
-       void gpiod_set_raw_array_cansleep(unsigned int array_size,
-                                         struct gpio_desc **desc_array,
-                                         int *value_array)
+       void gpiod_set_array_value(unsigned int array_size,
+                                  struct gpio_desc **desc_array,
+                                  int *value_array)
+       void gpiod_set_raw_array_value(unsigned int array_size,
+                                      struct gpio_desc **desc_array,
+                                      int *value_array)
+       void gpiod_set_array_value_cansleep(unsigned int array_size,
+                                           struct gpio_desc **desc_array,
+                                           int *value_array)
+       void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
+                                               struct gpio_desc **desc_array,
+                                               int *value_array)
 
 The array can be an arbitrary set of GPIOs. The functions will try to set
 GPIOs belonging to the same bank or chip simultaneously if supported by the
@@ -271,8 +307,8 @@ matches the desired group of GPIOs, those GPIOs can be set by simply using
 the struct gpio_descs returned by gpiod_get_array():
 
        struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
-       gpiod_set_array(my_gpio_descs->ndescs, my_gpio_descs->desc,
-                       my_gpio_values);
+       gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
+                             my_gpio_values);
 
 It is also possible to set a completely arbitrary array of descriptors. The
 descriptors may be obtained using any combination of gpiod_get() and
@@ -290,7 +326,7 @@ corresponding to a given GPIO using the following call:
 
        int gpiod_to_irq(const struct gpio_desc *desc)
 
-It will return an IRQ number, or an negative errno code if the mapping can't be
+It will return an IRQ number, or a negative errno code if the mapping can't be
 done (most likely because that particular GPIO cannot be used as IRQ). It is an
 unchecked error to use a GPIO that wasn't set up as an input using
 gpiod_direction_input(), or to use an IRQ number that didn't originally come