[edk2-devel] VirtIO Sound Driver (GSoC 2021)

Fri Apr 16 17:03:51 UTC 2021

> On Apr 16, 2021, at 4:34 AM, Leif Lindholm <leif at nuviainc.com> wrote:
> 
> Hi Ethin,
> 
> I think we also want to have a SetMode function, even if we don't get
> around to implement proper support for it as part of GSoC (although I
> expect at least for virtio, that should be pretty straightforward).
> 

Leif,

I’m think if we have an API to load the buffer and a 2nd API to play the buffer an optional 3rd API could configure the streams. 

> It's quite likely that speech for UI would be stored as 8kHz (or
> 20kHz) in some systems, whereas the example for playing a tune in GRUB
> would more likely be a 44.1 kHz mp3/wav/ogg/flac.
> 
> For the GSoC project, I think it would be quite reasonable to
> pre-generate pure PCM streams for testing rather than decoding
> anything on the fly.
> 
> Porting/writing decoders is really a separate task from enabling the
> output. I would much rather see USB *and* HDA support able to play pcm
> streams before worrying about decoding.
> 

I agree it might turn out it is easier to have the text to speech code just encode a PCM directly. 

Thanks,

Andrew Fish

> /
>    Leif
> 
> On Fri, Apr 16, 2021 at 00:33:06 -0500, Ethin Probst wrote:
>> Thanks for that explanation (I missed Mike's message). Earlier I sent
>> a summary of those things that we can agree on: mainly, that we have
>> mute, volume control, a load buffer, (maybe) an unload buffer, and a
>> start/stop stream function. Now that I fully understand the
>> ramifications of this I don't mind settling for a specific format and
>> sample rate, and signed 16-bit PCM audio is, I think, the most widely
>> used one out there, besides 64-bit floating point samples, which I've
>> only seen used in DAWs, and that's something we don't need.
>> Are you sure you want the firmware itself to handle the decoding of
>> WAV audio? I can make a library class for that, but I'll definitely
>> need help with the security aspect.
>> 
>> On 4/16/21, Andrew Fish via groups.io <afish=apple.com at groups.io> wrote:
>>> 
>>> 
>>>> On Apr 15, 2021, at 5:59 PM, Michael Brown <mcb30 at ipxe.org> wrote:
>>>> 
>>>> On 16/04/2021 00:42, Ethin Probst wrote:
>>>>> Forcing a particular channel mapping, sample rate and sample format on
>>>>> everyone would complicate application code. From an application point
>>>>> of view, one would, with that type of protocol, need to do the
>>>>> following:
>>>>> 1) Load an audio file in any audio file format from any storage
>>>>> mechanism.
>>>>> 2) Decode the audio file format to extract the samples and audio
>>>>> metadata.
>>>>> 3) Resample the (now decoded) audio samples and convert (quantize) the
>>>>> audio samples into signed 16-bit PCM audio.
>>>>> 4) forward the samples onto the EFI audio protocol.
>>>> 
>>>> You have made an incorrect assumption that there exists a requirement to
>>>> be able to play audio files in arbitrary formats.  This requirement does
>>>> not exist.
>>>> 
>>>> With a protocol-mandated fixed baseline set of audio parameters (sample
>>>> rate etc), what would happen in practice is that the audio files would be
>>>> encoded in that format at *build* time, using tools entirely external to
>>>> UEFI.  The application code is then trivially simple: it just does "load
>>>> blob, pass blob to audio protocol".
>>>> 
>>> 
>>> 
>>> Ethin,
>>> 
>>> Given the goal is an industry standard we value interoperability more that
>>> flexibility.
>>> 
>>> How about another use case. Lets say the Linux OS loader (Grub) wants to
>>> have an accessible UI so it decides to sore sound files on the EFI System
>>> Partition and use our new fancy UEFI Audio Protocol to add audio to the OS
>>> loader GUI. So that version of Grub needs to work on 1,000 of different PCs
>>> and a wide range of UEFI Audio driver implementations. It is a much easier
>>> world if Wave PCM 16 bit just works every place. You could add a lot of
>>> complexity and try to encode the audio on the fly, maybe even in Linux
>>> proper but that falls down if you are booting from read only media like a
>>> DVD or backup tape (yes people still do that in server land).
>>> 
>>> The other problem with flexibility is you just made the test matrix very
>>> large for every driver that needs to get implemented. For something as
>>> complex as Intel HDA how you hook up the hardware and what CODECs you use
>>> may impact the quality of the playback for a given board. Your EFI is likely
>>> going to pick a single encoding at that will get tested all the time if your
>>> system has audio, but all 50 other things you support not so much. So that
>>> will required testing, and some one with audiophile ears (or an AI program)
>>> to test all the combinations. I’m not kidding I get BZs on the quality of
>>> the boot bong on our systems.
>>> 
>>> 
>>>>> typedef struct EFI_SIMPLE_AUDIO_PROTOCOL {
>>>>>  EFI_SIMPLE_AUDIO_PROTOCOL_RESET Reset;
>>>>>  EFI_SIMPLE_AUDIO_PROTOCOL_START Start;
>>>>>  EFI_SIMPLE_AUDIO_PROTOCOL_STOP Stop;
>>>>> } EFI_SIMPLE_AUDIO_PROTOCOL;
>>>> 
>>>> This is now starting to look like something that belongs in boot-time
>>>> firmware.  :)
>>>> 
>>> 
>>> I think that got a little too simple I’d go back and look at the example I
>>> posted to the thread but add an API to load the buffer, and then play the
>>> buffer (that way we can an API in the future to twiddle knobs). That API
>>> also implements the async EFI interface. Trust me the 1st thing that is
>>> going to happen when we add audio is some one is going to complain in xyz
>>> state we should mute audio, or we should honer audio volume and mute
>>> settings from setup, or from values set in the OS. Or some one is going to
>>> want the volume keys on the keyboard to work in EFI.
>>> 
>>> Also if you need to pick apart the Wave PCM 16 byte file to feed it into the
>>> audio hardware that probably means we should have a library that does that
>>> work, so other Audio drivers can share that code. Also having a library
>>> makes it easier to write a unit test. We need to be security conscious as we
>>> need to treat the Audo file as attacker controlled data.
>>> 
>>> Thanks,
>>> 
>>> Andrew Fish
>>> 
>>>> Michael
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>> 
>> 
>> -- 
>> Signed,
>> Ethin D. Probst
> 
> 
> 
> 
> 

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