Re: [PATCH net-next v4 2/2] of: net: fix of_get_mac_addr_nvmem() for non-platform devices

[Michael Walle]

Am 2021-04-16 05:24, schrieb Benjamin Herrenschmidt:
> On Mon, 2021-04-12 at 19:47 +0200, Michael Walle wrote:
> >  /**
> >   * of_get_phy_mode - Get phy mode for given device_node
> > @@ -59,15 +60,39 @@ static int of_get_mac_addr(struct device_node *np, 
> > const char *name, 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;
> > +       }
> > +
>
> This smells like the wrong band aid :)
>
> Any struct device can contain an OF node pointer these days.

But not all nodes might have an associated device, see DSA for example.
And as the name suggests of_get_mac_address() operates on a node. So
if a driver calls of_get_mac_address() it should work on the node. What
is wrong IMHO, is that the ethernet drivers where the corresponding 
board
has a nvmem_cell_lookup registered is calling of_get_mac_address(node).
It should rather call eth_get_mac_address(dev) in the first place.

One would need to figure out if there is an actual device (with an
assiciated of_node), then call eth_get_mac_address(dev) and if there
isn't a device call of_get_mac_address(node).

But I don't know if that is easy to figure out. Well, one could start
with just the device where nvmem_cell_lookup is used. Then we could
drop the workaround above.

> This seems all backwards. I think we are dealing with bad evolution.
>
> We need to do a lookup for the device because we get passed an of_node.
> We should just get passed a device here... or rather stop calling
> of_get_mac_addr() from all those drivers and instead call
> eth_platform_get_mac_address() which in turns calls of_get_mac_addr().
>
> Then the nvmem stuff gets put in eth_platform_get_mac_address().
>
> of_get_mac_addr() becomes a low-level thingy that most drivers don't
> care about.

The NVMEM thing is just another (optional) way how the MAC address
is fetched from the device tree. Thus, if the drivers have the
of_get_mac_address() call they should automatically get the NVMEM
method, too.

-michael