Re: [PATCH] of: net: support NVMEM cells with MAC in text format

[Michael Walle]

Am 2021-12-29 19:18, schrieb Jakub Kicinski:
> On Wed, 29 Dec 2021 13:40:47 +0100 Michael Walle wrote:
> > > Some NVMEM devices have text based cells. In such cases MAC is stored in
> > > a XX:XX:XX:XX:XX:XX format. Use mac_pton() to parse such data and
> > > support those NVMEM cells. This is required to support e.g. a very
> > > popular U-Boot and its environment variables.
> > >
> > > Signed-off-by: Rafał Miłecki <rafal@xxxxxxxxxx>
> > > ---
> > > Please let me know if checking NVMEM cell length (6 B vs. 17 B) can be
> > > considered a good enough solution. Alternatively we could use some DT
> > > property to make it explicity, e.g. something like:
> > >
> > > ethernet@18024000 {
> > > 	compatible = "brcm,amac";
> > > 	reg = <0x18024000 0x800>;
> > >
> > > 	nvmem-cells = <&mac_addr>;
> > > 	nvmem-cell-names = "mac-address";
> > > 	nvmem-mac-format = "text";
> > > };
> >
> > Please note, that there is also this proposal, which had such a 
> > conversion
> > in mind:
> > https://lore.kernel.org/linux-devicetree/20211228142549.1275412-1-michael@xxxxxxxx/
> >
> > With this patch, there are now two different places where a mac 
> > address
> > format is converted. In of_get_mac_addr_nvmem() and in the imx otp 
> > driver.
> > And both have their shortcomings and aren't really flexible. Eg. this 
> > one
> > magically detects the format by comparing the length, but can't be 
> > used for
> > to swap bytes (because the length is also ETH_ALEN), which apparently 
> > is a
> > use case in the imx otp driver. And having the conversion in an nvmem
> > provider device driver is still a bad thing IMHO.
> >
> > I'd really like to see all these kind of transformations in one place.
>
> FWIW offsetting from a common base address is relatively common, that's
> why we have:
>
> /**
>  * eth_hw_addr_gen - Generate and assign Ethernet address to a port
>  * @dev: pointer to port's net_device structure
>  * @base_addr: base Ethernet address
>  * @id: offset to add to the base address
>  *
>  * Generate a MAC address using a base address and an offset and assign 
> it
>  * to a net_device. Commonly used by switch drivers which need to 
> compute
>  * addresses for all their ports. addr_assign_type is not changed.
>  */
> static inline void eth_hw_addr_gen(struct net_device *dev, const u8 
> *base_addr,
> 				   unsigned int id)

I didn't know that. But it doesn't help me that much because it mostly
used for switches, but in my case, I also have up to four network
cards (enetc) on the SoC; besides a network switch (felix). But
only one source for the base mac address.

-michael