linux-kernel - Re: [RFC PATCH 04/14] sound: usb: card: Introduce USB SND vendor op callbacks

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Date:   Tue, 3 Jan 2023 13:20:48 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Wesley Cheng <quic_wcheng@...cinc.com>,
        Takashi Iwai <tiwai@...e.de>, Oliver Neukum <oneukum@...e.com>
Cc:     srinivas.kandagatla@...aro.org, mathias.nyman@...el.com,
        perex@...ex.cz, broonie@...nel.org, lgirdwood@...il.com,
        andersson@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        gregkh@...uxfoundation.org, Thinh.Nguyen@...opsys.com,
        bgoswami@...cinc.com, tiwai@...e.com, robh+dt@...nel.org,
        agross@...nel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
        quic_jackp@...cinc.com, quic_plai@...cinc.com
Subject: Re: [RFC PATCH 04/14] sound: usb: card: Introduce USB SND vendor op
 callbacks



On 30.12.22 08:10, Wesley Cheng wrote:

> 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.

You would presumably output garbage, if the UDEV is asleep but the backend is not.

  
> 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.

How? If we go the reset_resume() code path, we find that usb-audio does not make
a difference between regular resume() and reset_resume()

	Regards
		Oliver