linux-kernel - Re: [PATCH] of_net: Implement of_get_nvmem_mac

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Date:   Fri, 23 Mar 2018 16:11:01 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Mike Looijmans <mike.looijmans@...ic.nl>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, f.fainelli@...il.com,
        robh+dt@...nel.org, frowand.list@...il.com
Subject: Re: [PATCH] of_net: Implement of_get_nvmem_mac_address helper

On Fri, Mar 23, 2018 at 03:24:34PM +0100, Mike Looijmans wrote:
> It's common practice to store MAC addresses for network interfaces into
> nvmem devices. However the code to actually do this in the kernel lacks,
> so this patch adds of_get_nvmem_mac_address() for drivers to obtain the
> address from an nvmem cell provider.
> 
> This is particulary useful on devices where the ethernet interface cannot
> be configured by the bootloader, for example because it's in an FPGA.
> 
> Tested by adapting the cadence macb driver to call this instead of
> of_get_mac_address().

Hi Mike

Please can you document the device tree binding. I assume you are
adding a nvmen-cells and nvmem-cell-names to the Ethernet node in
device tree.

> +/**
> + * Search the device tree for a MAC address, by calling of_get_mac_address
> + * and if that doesn't provide an address, fetch it from an nvmem provider
> + * using the name 'mac-address'.
> + * On success, copies the new address is into memory pointed to by addr and
> + * returns 0. Returns a negative error code otherwise.
> + * @dev:	Pointer to the device containing the device_node
> + * @addr:	Pointer to receive the MAC address using ether_addr_copy()
> + */
> +int of_get_nvmem_mac_address(struct device *dev, char *addr)
> +{
> +	const char *mac;
> +	struct nvmem_cell *cell;
> +	size_t len;
> +	int ret;
> +
> +	mac = of_get_mac_address(dev->of_node);
> +	if (mac) {
> +		ether_addr_copy(addr, mac);
> +		return 0;
> +	}

Is there a need to add a new API? Could of_get_mac_address() be
extended to look in NVMEM? The MAC driver does not care. It is saying,
using OF get me a MAC address. One API seems sufficient, and would
mean you don't need to change the MAC drivers.

     Andrew