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.
static int dev;
....
if (dev >= SNDRV_CARDS)
return -ENODEV;
if (!enable[dev]) {
dev++;
return -ENOENT;
}
where enable[dev] is the module option.
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).
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.
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;
}
The details will be explained in the section PCI Resource Management.
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 driver field holds the minimal ID string of the chip. This is used by alsa-lib's configurator, so keep it simple but unique. Even the same driver can have different driver IDs to distinguish the functionality of each chip type.
The shortname field is a string shown as more verbose
name. The longname field contains the information
shown in /proc/asound/cards.
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.
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.