Re: [PATCH 2/2] of: net: fix of_get_mac_addr_nvmem() for PCI and DSA nodes

[Andrew Lunn <andrew@lunn.ch>]

On Mon, Apr 05, 2021 at 11:46:04PM +0200, Michael Walle wrote:
> Hi Andrew,
> 
> Am 2021-04-05 23:34, schrieb Andrew Lunn:
> > > -static int of_get_mac_addr_nvmem(struct device_node *np, u8 addr)
> > > +static int of_get_mac_addr_nvmem(struct device_node *np, u8 *addr)
> > >  {
> > >  	struct platform_device *pdev = of_find_device_by_node(np);
> > > +	struct nvmem_cell *cell;
> > > +	const void *mac;
> > > +	size_t len;
> > >  	int ret;
> > > 
> > > -	if (!pdev)
> > > -		return -ENODEV;
> > > +	/* Try lookup by device first, there might be a nvmem_cell_lookup
> > > +	 * associated with a given device.
> > > +	 */
> > > +	if (pdev) {
> > > +		ret = nvmem_get_mac_address(&pdev->dev, addr);
> > > +		put_device(&pdev->dev);
> > > +		return ret;
> > > +	}
> > 
> > Can you think of any odd corner case where nvmem_get_mac_address()
> > would fail, but of_nvmem_cell_get(np, "mac-address") would work?
> 
> You mean, it might make sense to just return here when
> nvmem_get_mac_address() will succeed and fall back to the
> of_nvmem_cell_get() in case of an error?

I've not read the documentation for nvmem_get_mac_address(). I was
thinking we might want to return real errors, and -EPROBE_DEFER. But
maybe with -ENODEV we should try of_nvmem_cell_get()?

But i'm not sure if there are any real use cases? The only thing i can
think of is if np points to something deeper inside the device tree
than what pdev does?

     Andrew