target/linux/generic-2.6/patches-2.6.25/962-backport_gpiolib_dynamic_gpio_number_allocation.patch

   1 From: Anton Vorontsov <avorontsov@ru.mvista.com>
   2 Date: Mon, 28 Apr 2008 09:14:46 +0000 (-0700)
   3 Subject: gpiolib: dynamic gpio number allocation
   4 X-Git-Tag: v2.6.26-rc1~848
   5 X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=8d0aab2f16c4fa170f32e7a74a52cd0122bbafef
   6
   7 gpiolib: dynamic gpio number allocation
   8
   9 If gpio_chip->base is negative during registration, gpiolib performs dynamic
  10 base allocation.  This is useful for devices that aren't always present, such
  11 as GPIOs on hotplugged devices rather than mainboards.  (This behavior was
  12 previously specified but not implemented.)
  13
  14 To avoid using any numbers that may have been explicitly assigned but not yet
  15 registered, this dynamic allocation assigns GPIO numbers from the biggest
  16 number on down, instead of from the smallest on up.
  17
  18 Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
  19 Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
  20 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  21 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  22 ---
  23
  24 --- a/drivers/gpio/gpiolib.c
  25 +++ b/drivers/gpio/gpiolib.c
  26 @@ -80,6 +80,33 @@
  27         return gpio_desc[gpio].chip;
  28  }
  29
  30 +/* dynamic allocation of GPIOs, e.g. on a hotplugged device */
  31 +static int gpiochip_find_base(int ngpio)
  32 +{
  33 +       int i;
  34 +       int spare = 0;
  35 +       int base = -ENOSPC;
  36 +
  37 +       for (i = ARCH_NR_GPIOS - 1; i >= 0 ; i--) {
  38 +               struct gpio_chip *chip = gpio_desc[i].chip;
  39 +
  40 +               if (!chip) {
  41 +                       spare++;
  42 +                       if (spare == ngpio) {
  43 +                               base = i;
  44 +                               break;
  45 +                       }
  46 +               } else {
  47 +                       spare = 0;
  48 +                       i -= chip->ngpio - 1;
  49 +               }
  50 +       }
  51 +
  52 +       if (gpio_is_valid(base))
  53 +               pr_debug("%s: found new base at %d\n", __func__, base);
  54 +       return base;
  55 +}
  56 +
  57  /**
  58   * gpiochip_add() - register a gpio_chip
  59   * @chip: the chip to register, with chip->base initialized
  60 @@ -88,38 +115,49 @@
  61   * Returns a negative errno if the chip can't be registered, such as
  62   * because the chip->base is invalid or already associated with a
  63   * different chip.  Otherwise it returns zero as a success code.
  64 + *
  65 + * If chip->base is negative, this requests dynamic assignment of
  66 + * a range of valid GPIOs.
  67   */
  68  int gpiochip_add(struct gpio_chip *chip)
  69  {
  70         unsigned long   flags;
  71         int             status = 0;
  72         unsigned        id;
  73 +       int             base = chip->base;
  74
  75 -       /* NOTE chip->base negative is reserved to mean a request for
  76 -        * dynamic allocation.  We don't currently support that.
  77 -        */
  78 -
  79 -       if (chip->base < 0 || !gpio_is_valid(chip->base  + chip->ngpio)) {
  80 +       if ((!gpio_is_valid(base) || !gpio_is_valid(base + chip->ngpio))
  81 +                       && base >= 0) {
  82                 status = -EINVAL;
  83                 goto fail;
  84         }
  85
  86         spin_lock_irqsave(&gpio_lock, flags);
  87
  88 +       if (base < 0) {
  89 +               base = gpiochip_find_base(chip->ngpio);
  90 +               if (base < 0) {
  91 +                       status = base;
  92 +                       goto fail_unlock;
  93 +               }
  94 +               chip->base = base;
  95 +       }
  96 +
  97         /* these GPIO numbers must not be managed by another gpio_chip */
  98 -       for (id = chip->base; id < chip->base + chip->ngpio; id++) {
  99 +       for (id = base; id < base + chip->ngpio; id++) {
 100                 if (gpio_desc[id].chip != NULL) {
 101                         status = -EBUSY;
 102                         break;
 103                 }
 104         }
 105         if (status == 0) {
 106 -               for (id = chip->base; id < chip->base + chip->ngpio; id++) {
 107 +               for (id = base; id < base + chip->ngpio; id++) {
 108                         gpio_desc[id].chip = chip;
 109                         gpio_desc[id].flags = 0;
 110                 }
 111         }
 112
 113 +fail_unlock:
 114         spin_unlock_irqrestore(&gpio_lock, flags);
 115  fail:
 116         /* failures here can mean systems won't boot... */