linux-kernel - Re: [PATCH net-next v4 1/7] queue_api: add support for fetching per queue DMA dev

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Message-ID: <20250820180100.7085a7d3@kernel.org>
Date: Wed, 20 Aug 2025 18:01:00 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: <almasrymina@...gle.com>, <asml.silence@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, <cratiu@...dia.com>,
 <parav@...dia.com>, <netdev@...r.kernel.org>, <sdf@...a.com>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v4 1/7] queue_api: add support for fetching per
 queue DMA dev

On Wed, 20 Aug 2025 20:11:52 +0300 Dragos Tatulea wrote:
> + * @ndo_queue_get_dma_dev: Get dma device for zero-copy operations to be used
> + *			   for this queue. When such device is not available,
> + *			   the function will return NULL.

nit: I think you're using a different tense/grammar than the doc for
other callbacks (which is admittedly somewhat unusual :$) 
Also should we indicate that "not available" is an error? Maybe just:

	Get dma device for zero-copy operations to be used
	for this queue. Return NULL on error.

>   * Note that @ndo_queue_mem_alloc and @ndo_queue_mem_free may be called while
>   * the interface is closed. @ndo_queue_start and @ndo_queue_stop will only
>   * be called for an interface which is open.

> +/**
> + * netdev_queue_get_dma_dev() - get dma device for zero-copy operations
> + * @dev:	net_device
> + * @idx:	queue index
> + *
> + * Get dma device for zero-copy operations to be used for this queue.
> + * When such device is not available or valid, the function will return NULL.

Unfortunately kdoc really wants us to add Return: statements to all
functions...

> + */
> +struct device *netdev_queue_get_dma_dev(struct net_device *dev, int idx)
> +{
> +	const struct netdev_queue_mgmt_ops *queue_ops = dev->queue_mgmt_ops;
> +	struct device *dma_dev;
> +
> +	if (queue_ops && queue_ops->ndo_queue_get_dma_dev)
> +		dma_dev = queue_ops->ndo_queue_get_dma_dev(dev, idx);
> +	else
> +		dma_dev = dev->dev.parent;
> +
> +	return dma_dev && dma_dev->dma_mask ? dma_dev : NULL;
> +}
> +EXPORT_SYMBOL(netdev_queue_get_dma_dev);
> \ No newline at end of file

This is in desperate need of a terminating new line.

But also -- why the export? iouring and devmem can't be modules.