Hi Greg,
On 2/27/2023 11:30 PM, Greg KH wrote:
On Mon, Feb 27, 2023 at 06:59:32PM -0800, Wesley Cheng wrote:
Hi Greg,
On 2/10/2023 2:49 PM, Wesley Cheng wrote:
Hi Greg,
On 1/28/2023 5:28 AM, Greg KH wrote:
On Wed, Jan 25, 2023 at 07:14:14PM -0800, Wesley Cheng wrote:
Allow for different platforms to be notified on USB SND
connect/disconnect
seqeunces. This allows for platform USB SND modules to properly
initialize
and populate internal structures with references to the USB SND chip
device.
Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
---
sound/usb/card.c | 28 ++++++++++++++++++++++++++++
sound/usb/card.h | 20 ++++++++++++++++++++
2 files changed, 48 insertions(+)
diff --git a/sound/usb/card.c b/sound/usb/card.c
index 26268ffb8274..803230343c16 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -117,6 +117,24 @@ MODULE_PARM_DESC(skip_validation, "Skip
unit descriptor validation (default: no)
static DEFINE_MUTEX(register_mutex);
static struct snd_usb_audio *usb_chip[SNDRV_CARDS];
static struct usb_driver usb_audio_driver;
+static struct snd_usb_platform_ops *platform_ops;
You can not have a single "platform_ops" pointer, this HAS to be
per-bus.
Agreed.
I looked at seeing how we could implement this at a per bus level, but the
USB class driver model doesn't exactly have a good framework for supporting
this. Reason being is because, at the time of the USB SND class driver
initialization, there is a big chance that there isn't a USB bus registered
in the system, so the point of adding the operations is not clear. However,
we need to ensure that we've added the platform/driver operations before any
USB SND devices are detected.
But the offload "engine" is associated with the specific USB bus
controller instance in the system, so perhaps you are just not adding
this to the correct location?
There are several parts to the offload logic:
1. XHCI interrupter/resource components - fetching addresses to the
proper event ring and transfer rings for the audio DSP. This is the
part which is specific to the controller instance, and APIs are being
directly exported from the XHCI HCD, as the offloading features utilized
are only specific for XHCI based controllers. This is handled in
patches 1-6 in this series. Each XHCI instance will have its own set of
interrupters, and transfer resources.
2. USB offload class driver - driver which interacts with USB SND for
operations like UAC descriptor parsing, USB audio device support params,
and USB endpoint setup (ie issuing SET_INTERFACE to enable the device to
start playback this is a SETUP transaction). It will interact with the
USB backend and items in #1, to set up the audio playback.
The sound core shouldn't care about this at all, add the logic to the
USB host controller driver instead, why isn't this just another USB bus
function?
The intention of the platform ops here is to mainly keep track of USB
SND card/pcm device creation, and access to the main "struct
snd_usb_audio". This structure carries all the information about the
different substreams allocated, as well as the formats supported by the
audio device. This is passed onto the USB backend, which will be
utilized in my next revision to allow userspace to specifically select
the proper card/PCM device to enable offload on.
To add to the above, in case of OTG/DRD (dual role) designs, the USB HCD/bus
isn't created until we move into the host role. At that time, using DWC3 as
an example, we will create the XHCI platform device, and probe the USB HCD,
where a USB bus is created.
Great, again, tie it to the specific xhci host controler instance.
In general, we currently think this USB offload driver should co-exist with
the USB SND class driver, which handles all devices connected across every
bus.
And that is incorrect, please do not do that.
To clarify, I think we can summarize that the qc_audio_offload driver
(the one that registers the platform operations) is mainly responsible
for USB SND card management, and communicating that to the USB backend.
We can add a check to the platform connect routine to ensure that
there is a reference to the USB backend. If so, then that particular USB
bus/sysdev can be supported by the audio DSP. That way, we do not falsely
populate USB SND cards which are present on another USB bus/controller.
You should NEVER be able to populate a USB card unless the USB bus
controller has given you the USB interface structure to control, so I do
not understand how this is an issue.
This might not be so clear with the current revision. In the next
revision I have prepared, as I mentioned, we are proposing using the
platform connect/disconnect ops here to build a reference to all USB SND
card and PCM devices available in the system.
For example, if you have an external hub connected to the root hub, and
each port on that hub has an audio device connected. We want to allow
userspace to select which card# and pcm# to start offload on. (versus
userspace having to rely on trail and error, which Pierre touched on on
why that is not desired)
Since the USB SND driver is based on udevs (not bus specific), if there
are multiple roothubs (correlates to usb buses), then we only want to
notify the USB backend of the USB SND cards on the controller which has
offloading enabled. Otherwise, if userspace selects a device on an
unsupported controller, then that path would obviously fail.
I hope that clarifies some things.
Thanks
Wesley Cheng
