linux-kernel - Re: [PATCH v7 06/33] ASoC: Add SOC USB APIs for adding an USB backend

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Message-ID: <ZRRAxSlk8uvsfMcx@finisterre.sirena.org.uk>
Date:   Wed, 27 Sep 2023 16:48:37 +0200
From:   Mark Brown <broonie@...nel.org>
To:     Wesley Cheng <quic_wcheng@...cinc.com>
Cc:     mathias.nyman@...el.com, gregkh@...uxfoundation.org,
        lgirdwood@...il.com, perex@...ex.cz, tiwai@...e.com,
        agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, srinivas.kandagatla@...aro.org,
        bgoswami@...cinc.com, Thinh.Nguyen@...opsys.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        alsa-devel@...a-project.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v7 06/33] ASoC: Add SOC USB APIs for adding an USB backend

On Thu, Sep 21, 2023 at 02:48:16PM -0700, Wesley Cheng wrote:

> +static struct device_node *snd_soc_find_phandle(struct device *dev)
> +{
> +	struct device_node *node;
> +
> +	node = of_parse_phandle(dev->of_node, "usb-soc-be", 0);

Very nitpicky but this function possibly wants a _usb_ in the name, not
that it *super* matters with it being static.  Or it could just be
inlined into the only user and not worry about the naming at all.

> +/**
> + * snd_soc_usb_get_priv_data() - Retrieve private data stored
> + * @dev: device reference
> + *
> + * Fetch the private data stored in the USB SND SOC structure.
> + *
> + */
> +void *snd_soc_usb_get_priv_data(struct device *dev)
> +{
> +	struct snd_soc_usb *ctx;
> +
> +	ctx = snd_soc_find_usb_ctx(dev);
> +	if (!ctx) {
> +		/* Check if backend device */
> +		mutex_lock(&ctx_mutex);
> +		list_for_each_entry(ctx, &usb_ctx_list, list) {
> +			if (dev->of_node == ctx->dev->of_node) {
> +				mutex_unlock(&ctx_mutex);
> +				goto out;
> +			}
> +		}
> +		mutex_unlock(&ctx_mutex);
> +		ctx = NULL;
> +	}

This seems a lot more expensive than I'd expect for a get_priv_data
operation, usually it's just a container_of() or other constant time
pulling out of a pointer rather than a linked list walk - the sort of
thing that people put at the start of functions and do all the time.
If we need this I think it needs a name that's more clearly tied to the
use case.

I didn't actually find the user of this though?

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