netdev - Re: [PATCH 4/5] net: add support for nvmem to eth_platform_get_mac

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Message-ID: <20180719152222.GD9119@lunn.ch>
Date:   Thu, 19 Jul 2018 17:22:22 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Sekhar Nori <nsekhar@...com>, Kevin Hilman <khilman@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Lukas Wunner <lukas@...ner.de>, Rob Herring <robh@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        David Lechner <david@...hnology.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, netdev@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 4/5] net: add support for nvmem to
 eth_platform_get_mac_address()

On Wed, Jul 18, 2018 at 06:10:34PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> Many non-DT platforms read the MAC address from EEPROM. Usually it's
> either done with callbacks defined in board files or from SoC-specific
> ethernet drivers.
> 
> In order to generalize this, try to read the MAC from nvmem in
> eth_platform_get_mac_address() using a standard lookup name:
> "mac-address".
> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> ---
>  net/ethernet/eth.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
> index 6b64586fd2af..adf5bd03851f 100644
> --- a/net/ethernet/eth.c
> +++ b/net/ethernet/eth.c
> @@ -54,6 +54,7 @@
>  #include <linux/if_ether.h>
>  #include <linux/of_net.h>
>  #include <linux/pci.h>
> +#include <linux/nvmem-consumer.h>
>  #include <net/dst.h>
>  #include <net/arp.h>
>  #include <net/sock.h>
> @@ -530,7 +531,10 @@ int eth_platform_get_mac_address(struct device *dev, u8 *mac_addr)
>  	struct device_node *dp = dev_is_pci(dev) ?
>  			pci_device_to_OF_node(to_pci_dev(dev)) : dev->of_node;
>  	const unsigned char *addr = NULL;
> +	unsigned char addrbuf[ETH_ALEN];
> +	struct nvmem_cell *nvmem;
>  	const char *from = NULL;
> +	size_t alen;
>  
>  	if (dp) {
>  		addr = of_get_mac_address(dp);
> @@ -544,6 +548,31 @@ int eth_platform_get_mac_address(struct device *dev, u8 *mac_addr)
>  			from = "arch callback";
>  	}
>  
> +	if (!addr) {
> +		nvmem = nvmem_cell_get(dev, "mac-address");
> +		if (IS_ERR(nvmem) && PTR_ERR(nvmem) == -EPROBE_DEFER)

How does EPROBE_DEFER work here? You say the use case is
Non-DT. Without having DT, how do you know the cell should exist, but
does not yet exist? I might be looking at old code, but i only see
-EPROBE_DEFER inside the if (np) case.

> +			/* We may have a lookup registered for MAC address but
> +			 * the corresponding nvmem provider hasn't been
> +			 * registered yet.
> +			 */
> +			return -EPROBE_DEFER;

You really should return real errors. If i'm reading
__nvmem_device_get() right, it will return a NULL pointer when the
cell does not exist. NULL is not an error, so IS_ERR() will return
false. So you should return all errors from nvmem_cell_get().

       Andrew