[edk2-devel] VirtIO Sound Driver (GSoC 2021)
Michael Brown
mcb30 at ipxe.org
Thu Apr 15 12:07:06 UTC 2021
On 15/04/2021 06:28, Ethin Probst wrote:
> - I hoped to add recording in case we in future want to add
> accessibility aids like speech recognition (that was one of the todo
> tasks on the EDK2 tasks list)
Is there any necessity for audio input and output to be implemented
within the same protocol? Unlike a network device (which is
intrinsically bidirectional), it seems natural to conceptually separate
audio input from audio output.
> - Muting and volume control could easily be added by just replacing
> the sample buffer with silence and by multiplying all the samples by a
> percentage.
The code controlling volume/mute may not have any access to the sample
buffer. The most natural implementation would seem to allow for a
platform to notice volume up/down keypresses and use those to control
the overall system volume, without any knowledge of which samples (if
any) are currently being played by other code in the system.
> - Finally, the reason I used enumerations for specifying parameters
> like sample rate and stuff was that I was looking at this protocol
> from a general UEFI applications point of view. VirtIO supports all of
> the sample configurations listed in my gist, and it seems reasonable
> to allow the application to control those parameters instead of
> forcing a particular parameter configuration onto the developer.
Consider also the point of view of the developer implementing a driver
for some other piece of audio hardware that happens not to support
precisely the same sample rates etc as VirtIO. It would be extremely
ugly to force all future hardware to pretend to have the same
capabilities as VirtIO just because the API was initially designed with
VirtIO in mind.
As a developer on the other side of the API, writing code to play sound
files on an arbitrary unknown platform, I would prefer to simply consume
as simple as possible an abstraction of an audio output protocol and not
have to care about what hardware is actually implementing it.
Both of these argue in favour of defining a very simple API that
expresses only a common baseline capability that is plausibly
implementable for every piece of audio hardware ever made.
Coupled with the relatively minimalistic requirements for boot-time
audio, I'd probably suggest supporting only a single format for audio
data, with a fixed sample rate (and possibly only mono output).
As always: perfection is achieved, not when there is nothing more to
add, but when there is nothing left to take away. :)
Thanks,
Michael
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