Eric Lee / linux-smarc-t335x-v3.2

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Commit c956126c137d97acb6f4d56fa9572d0bcc84e4ed

Authored by David Brownell
Committed by Linus Torvalds
1 parent 5affb60772
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

gpio: doc updates 

There's been some recent confusion about error checking GPIO numbers.
briefly, it should be handled mostly during setup, when gpio_request() is
called, and NEVER by expectig gpio_is_valid to report more than
never-usable GPIO numbers.

[akpm@linux-foundation.org: terminate unterminated comment]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Eric Miao" <eric.y.miao@gmail.com>
Cc: "Ryan Mallon" <ryan@bluewatersys.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 2 changed files with 27 additions and 9 deletions Side-by-side Diff

Documentation/gpio.txt
Diff comments   View file @ c956126
... ... @@ -109,18 +109,20 @@
109 109  
110 110 If you want to initialize a structure with an invalid GPIO number, use
111 111 some negative number (perhaps "-EINVAL"); that will never be valid. To
112   -test if a number could reference a GPIO, you may use this predicate:
  112 +test if such number from such a structure could reference a GPIO, you
  113 +may use this predicate:
113 114  
114 115 int gpio_is_valid(int number);
115 116  
116 117 A number that's not valid will be rejected by calls which may request
117 118 or free GPIOs (see below). Other numbers may also be rejected; for
118   -example, a number might be valid but unused on a given board.
  119 +example, a number might be valid but temporarily unused on a given board.
119 120  
120   -Whether a platform supports multiple GPIO controllers is currently a
121   -platform-specific implementation issue.
  121 +Whether a platform supports multiple GPIO controllers is a platform-specific
  122 +implementation issue, as are whether that support can leave "holes" in the space
  123 +of GPIO numbers, and whether new controllers can be added at runtime. Such issues
  124 +can affect things including whether adjacent GPIO numbers are both valid.
122 125  
123   -
124 126 Using GPIOs
125 127 -----------
126 128 The first thing a system should do with a GPIO is allocate it, using
127 129  
128 130  
... ... @@ -480,12 +482,16 @@
480 482 ARCH_REQUIRE_GPIOLIB or ARCH_WANT_OPTIONAL_GPIOLIB
481 483 and arrange that its <asm/gpio.h> includes <asm-generic/gpio.h> and defines
482 484 three functions: gpio_get_value(), gpio_set_value(), and gpio_cansleep().
483   -They may also want to provide a custom value for ARCH_NR_GPIOS.
484 485  
485   -ARCH_REQUIRE_GPIOLIB means that the gpio-lib code will always get compiled
  486 +It may also provide a custom value for ARCH_NR_GPIOS, so that it better
  487 +reflects the number of GPIOs in actual use on that platform, without
  488 +wasting static table space. (It should count both built-in/SoC GPIOs and
  489 +also ones on GPIO expanders.
  490 +
  491 +ARCH_REQUIRE_GPIOLIB means that the gpiolib code will always get compiled
486 492 into the kernel on that architecture.
487 493  
488   -ARCH_WANT_OPTIONAL_GPIOLIB means the gpio-lib code defaults to off and the user
  494 +ARCH_WANT_OPTIONAL_GPIOLIB means the gpiolib code defaults to off and the user
489 495 can enable it and build it into the kernel optionally.
490 496  
491 497 If neither of these options are selected, the platform does not support
include/asm-generic/gpio.h
Diff comments   View file @ c956126
... ... @@ -16,15 +16,27 @@
16 16 * While the GPIO programming interface defines valid GPIO numbers
17 17 * to be in the range 0..MAX_INT, this library restricts them to the
18 18 * smaller range 0..ARCH_NR_GPIOS-1.
  19 + *
  20 + * ARCH_NR_GPIOS is somewhat arbitrary; it usually reflects the sum of
  21 + * builtin/SoC GPIOs plus a number of GPIOs on expanders; the latter is
  22 + * actually an estimate of a board-specific value.
19 23 */
20 24  
21 25 #ifndef ARCH_NR_GPIOS
22 26 #define ARCH_NR_GPIOS 256
23 27 #endif
24 28  
  29 +/*
  30 + * "valid" GPIO numbers are nonnegative and may be passed to
  31 + * setup routines like gpio_request(). only some valid numbers
  32 + * can successfully be requested and used.
  33 + *
  34 + * Invalid GPIO numbers are useful for indicating no-such-GPIO in
  35 + * platform data and other tables.
  36 + */
  37 +
25 38 static inline int gpio_is_valid(int number)
26 39 {
27   - /* only some non-negative numbers are valid */
28 40 return ((unsigned)number) < ARCH_NR_GPIOS;
29 41 }
30 42