This commit uses the ack() callback to determine when a buffer has been
updated, then exposes it to guest.
The current mechanism splits a dma buffer into descriptors that are
exposed to the device. This dma buffer is shared with the user
application. When the device consumes a buffer, the driver moves the
request from the used ring to available ring.
The driver exposes the buffer to the device without knowing if the
content has been updated from the user. The section 2.8.21.1 of the
virtio spec states that: "The device MAY access the descriptor chains
the driver created and the memory they refer to immediately". If the
device picks up buffers from the available ring just after it is
notified, it happens that the content may be old.
When the ack() callback is invoked, the driver exposes only the buffers
that have already been updated, i.e., enqueued in the available ring.
Thus, the device always picks up a buffer that is updated.
For capturing, the driver starts by exposing all the available buffers
to device. After device updates the content of a buffer, it enqueues it
in the used ring. It is only after the ack() for capturing is issued
that the driver re-enqueues the buffer in the available ring.
Co-developed-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
Link: https://lore.kernel.org/r/ZTjkn1YAFz67yfqx@fedora
Signed-off-by: Takashi Iwai <tiwai@suse.de>
The driver implements a message-based transport for I/O substream
operations. Before the start of the substream, the hardware buffer is
sliced into I/O messages, the number of which is equal to the current
number of periods. The size of each message is equal to the current
size of one period.
I/O messages are organized in an ordered queue. The completion of the
I/O message indicates an elapsed period (the only exception is the end
of the stream for the capture substream). Upon completion, the message
is automatically re-added to the end of the queue.
Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
Link: https://lore.kernel.org/r/20210302164709.3142702-6-anton.yakovlev@opensynergy.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Like the HDA specification, the virtio sound device specification links
PCM substreams, jacks and PCM channel maps into functional groups. For
each discovered group, a PCM device is created, the number of which
coincides with the group number.
Introduce the module parameters for setting the hardware buffer
parameters:
pcm_buffer_ms [=160]
pcm_periods_min [=2]
pcm_periods_max [=16]
pcm_period_ms_min [=10]
pcm_period_ms_max [=80]
Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
Link: https://lore.kernel.org/r/20210302164709.3142702-5-anton.yakovlev@opensynergy.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
