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Date:   Mon, 7 Mar 2022 08:55:18 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Oh Eomji <eomji.oh@samsung.com>
Cc:     Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
        open list <linux-kernel@vger.kernel.org>,
        alsa-devel@alsa-project.org, Leon Romanovsky <leon@kernel.org>,
        Pavel Skripkin <paskripkin@gmail.com>,
        JaeHun Jung <jh0801.jung@samsung.com>
Subject: Re: [PATCH 1/2] sound: usb: Add vendor's hooking interface
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References: <CGME20220307022409epcas2p4a2955a746c87d66564556e18ab94845f@epcas2p4.samsung.com>
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On Mon, Mar 07, 2022 at 11:21:59AM +0900, Oh Eomji wrote:
> In mobile, a co-processor can be used with USB audio to improve power
> consumption.  To support this type of hardware, hooks need to be added
> to the USB audio subsystem to be able to call into the hardware when
> needed.
> 
> The main operation of the call-backs are:
>   - Initialize the co-processor by transmitting data when initializing.
>   - Change the co-processor setting value through the interface
>     function.
>   - Configure sampling rate
>   - pcm open/close
>   - other housekeeping
> 
> Known issues:
>   - This only supports one set of callback hooks, meaning that this only
>     works if there is one type of USB controller in the system.  This
>     should be changed to be a per-host-controller interface instead of
>     one global set of callbacks.

Also, this is a non-starter, and not going to work at all, sorry.  Most
devices have more than one USB controller in the system, and we can
never accept changes that break that model.

Nor would you want us to, as it would break many Samsung devices...

thanks,

greg k-h