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ALSA: usb-audio: Update the documentation for the new delayed_register option

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Just adding a brief explanation to alsa-configuration.rst.

Link: https://lore.kernel.org/r/20200325103322.2508-5-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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Takashi Iwai 2020-03-25 11:33:22 +01:00
parent a4aad5636c
commit 2ceb65cd04
1 changed files with 13 additions and 0 deletions
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Documentation/sound/alsa-configuration.rst
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@ -2234,6 +2234,19 @@ use_vmalloc
buffers. If mmap is used on such architectures, turn off this
option, so that the DMA-coherent buffers are allocated and used
instead.
delayed_register
The option is needed for devices that have multiple streams
defined in multiple USB interfaces. The driver may invoke
registrations multiple times (once per interface) and this may
lead to the insufficient device enumeration.
This option receives an array of strings, and you can pass
ID:INTERFACE like ``0123abcd:4`` for performing the delayed
registration to the given device. In this example, when a USB
device 0123:abcd is probed, the driver waits the registration
until the USB interface 4 gets probed.
The driver prints a message like "Found post-registration device
assignment: 1234abcd:04" for such a device, so that user can
notice the need.
This module supports multiple devices, autoprobe and hotplugging.