Re: [PATCH v2 net-next] net: Allow SF devices to be used for ZC DMA

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 11 Jul 2025 09:26:34 +0000 Dragos Tatulea wrote:
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 5847c20994d3..53aa63d6e5a3 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -5560,4 +5560,25 @@ extern struct net_device *blackhole_netdev;
>  		atomic_long_add((VAL), &(DEV)->stats.__##FIELD)
>  #define DEV_STATS_READ(DEV, FIELD) atomic_long_read(&(DEV)->stats.__##FIELD)
>  
> +static inline struct device *netdev_get_dma_dev(const struct net_device *dev)
> +{
> +	struct device *dma_dev = dev->dev.parent;
> +
> +	if (!dma_dev)
> +		return NULL;
> +
> +	/* Common case: dma device is parent device of netdev. */
> +	if (dma_dev->dma_mask)
> +		return dma_dev;
> +
> +	/* SF netdevs have an auxdev device as parent, the dma device being the
> +	 * grandparent.
> +	 */
> +	dma_dev = dma_dev->parent;
> +	if (dma_dev && dma_dev->dma_mask)
> +		return dma_dev;
> +
> +	return NULL;
> +}

LGTM, but we need a better place for this function. netdevice.h is
included directly by 1.5k files, and indirectly by probably another 5k.
It's not a great place to put random helpers with 2 callers. 
Maybe net/netdev_rx_queue.h and net/core/netdev_rx_queue.c?
I don't think it needs to be a static inline either.
-- 
pw-bot: cr