Constructor

1) Check and increment the device index.
2) Create a card instance
3) Create a main component
4) Set the driver ID and name strings.
5) Create other components, such as mixer, MIDI, etc.
6) Register the card instance.
7) Set the PCI driver data and return zero.

The real constructor of PCI drivers is the probe callback. The probe callback and other component-constructors which are called from the probe callback should be defined with the __devinit prefix. You cannot use the __init prefix for them, because any PCI device could be a hotplug device.

In the probe callback, the following scheme is often used.

1) Check and increment the device index.


  static int dev;
  ....
  if (dev >= SNDRV_CARDS)
          return -ENODEV;
  if (!enable[dev]) {
          dev++;
          return -ENOENT;
  }

            

Each time the probe callback is called, check the availability of the device. If not available, simply increment the device index and returns. dev will be incremented also later (step 7).

2) Create a card instance


  struct snd_card *card;
  int err;
  ....
  err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card);

            

The details will be explained in the section Management of Cards and Components.

3) Create a main component

In this part, the PCI resources are allocated.


  struct mychip *chip;
  ....
  err = snd_mychip_create(card, pci, &chip);
  if (err < 0) {
          snd_card_free(card);
          return err;
  }

            

4) Set the driver ID and name strings.


  strcpy(card->driver, "My Chip");
  strcpy(card->shortname, "My Own Chip 123");
  sprintf(card->longname, "%s at 0x%lx irq %i",
          card->shortname, chip->ioport, chip->irq);

            

The shortname field is a string shown as more verbose name. The longname field contains the information shown in /proc/asound/cards.

5) Create other components, such as mixer, MIDI, etc.

Here you define the basic components such as PCM, mixer (e.g. AC97), MIDI (e.g. MPU-401), and other interfaces. Also, if you want a proc file, define it here, too.

6) Register the card instance.


  err = snd_card_register(card);
  if (err < 0) {
          snd_card_free(card);
          return err;
  }

            

Will be explained in the section Management of Cards and Components, too.

7) Set the PCI driver data and return zero.


        pci_set_drvdata(pci, card);
        dev++;
        return 0;