linux-kernel - Re: [PATCH v4 19/32] sound: usb: card: Check for support for requested audio format

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Message-ID: <87cz0gv5pd.wl-tiwai@suse.de>
Date:   Tue, 25 Jul 2023 08:57:34 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Wesley Cheng <quic_wcheng@...cinc.com>
Cc:     <agross@...nel.org>, <andersson@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <catalin.marinas@....com>, <will@...nel.org>,
        <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>,
        <lgirdwood@...il.com>, <broonie@...nel.org>, <perex@...ex.cz>,
        <tiwai@...e.com>, <srinivas.kandagatla@...aro.org>,
        <bgoswami@...cinc.com>, <Thinh.Nguyen@...opsys.com>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-usb@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <quic_jackp@...cinc.com>, <pierre-louis.bossart@...ux.intel.com>,
        <oneukum@...e.com>, <albertccwang@...gle.com>,
        <o-takashi@...amocchi.jp>
Subject: Re: [PATCH v4 19/32] sound: usb: card: Check for support for requested audio format

On Tue, 25 Jul 2023 04:34:03 +0200,
Wesley Cheng wrote:
> 
> Allow for checks on a specific USB audio device to see if a requested PCM
> format is supported.  This is needed for support for when playback is
> initiated by the ASoC USB backend path.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
> ---
>  sound/usb/card.c | 28 ++++++++++++++++++++++++++++
>  sound/usb/card.h |  8 ++++++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index a3fad66a3337..365f6d978608 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -142,6 +142,34 @@ int snd_usb_unregister_platform_ops(void)
>  }
>  EXPORT_SYMBOL_GPL(snd_usb_unregister_platform_ops);
>  
> +struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
> +			struct snd_pcm_hw_params *params, int direction)
> +{

Please add a comment what this function does.


> +	struct snd_usb_audio *chip = usb_chip[card_idx];

Is the dereference safe without locking?
If the call is supposed to be allowed only in a safe situation, it
should be mentioned in the function description.


thanks,

Takashi