Hi,
On 12/29/2022 6:20 AM, Takashi Iwai wrote:
On Thu, 29 Dec 2022 14:49:21 +0100, Oliver Neukum wrote:
On 24.12.22 00:31, Wesley Cheng wrote:
Allow for different vendors to be notified on USB SND connect/disconnect seqeunces. This allows for vendor USB SND modules to properly initialize and populate internal structures with references to the USB SND chip device.
Hi,
this raises a design question. If the system is suspending or, worse, hibernating, how do you make sure the offloader and the device are suspended in the correct order? And what happens if you need to go into reset_resume() when resuming?
It may depend on how the offloading is implemented, but we do have a mechanism to force the audio stream off from the qc_usb_audio_offload. Regardless of if the UDEV is suspended first, or the USB backend, as long as we ensure that the offloading is disabled before entering suspend, I think that should be sufficient. I would need to add some suspend handling in the offload driver to issue the command to stop the offloading.
As for the resume path, is there a concern if either device is resumed first? The only scenario where maybe it could cause some mishandling is if the USB backend is resumed before the offload driver is connected/resumed. This means that the userspace ALSA would have access to the platform sound card, and could potentially attempt to route audio streams to it. I think in worst case, if we were going through a reset_resume() we would end up rejecting that request coming from the audio DSP to enable the stream. However, userspace entities would be resumed/unfrozen last, so not sure if that would ever be a problem.
The reset_resume() path is fine. Bus reset is going to cause a disconnect() callback in the offload driver, in which we already have the proper handling for ensuring the offload path is halted, and we reject any incoming stream start requests.
Thanks Wesley Cheng