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SubjectRe: [PATCH] of: net: support NVMEM cells with MAC in text format
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@milecki.pl>
>> > ---
>> > 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@walle.cc/
>>
>> 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

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