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SubjectRe: [PATCH] [net] nvmem: disallow modular CONFIG_NVMEM
For making things build again:

Acked-by: Mike Looijmans

I'd be interested in use-cases for having nvmem as a module, I cannot think of

I am working on splitting of_get_nvmem_mac_address(), by moving most of its
burden to the nvmem interface. Intend to create this "just give me my bytes"
function in nvmem:

int of_nvmem_cell_read(struct device_node *np, const char *name,
void *buf, size_t bytes);

With that in place, of_get_nvmem_mac_address becomes a one-liner:

return of_nvmem_cell_read(np, "mac-address", addr, ETH_ALEN);

That would allow of_get_nvmem_mac_address to be inlined, and this would move
the link issues into modules that actually use that function.

Which may still be very confusing, since it means that CONFIG_MACB=y with
CONFIG_NVMEM=m will fail, but setting both to "y" or both to "m" will work. So
that would introduce more build failures again, right?


On 04-04-18 12:38, Arnd Bergmann wrote:
> The new of_get_nvmem_mac_address() helper function causes a link error
> with CONFIG_NVMEM=m:
> drivers/of/of_net.o: In function `of_get_nvmem_mac_address':
> of_net.c:(.text+0x168): undefined reference to `of_nvmem_cell_get'
> of_net.c:(.text+0x19c): undefined reference to `nvmem_cell_read'
> of_net.c:(.text+0x1a8): undefined reference to `nvmem_cell_put'
> I could not come up with a good solution for this, as the code is always
> built-in. Using an #if IS_REACHABLE() check around it would solve the
> link time issue but then stop it from working in that configuration.
> Making of_nvmem_cell_get() an inline function could also solve that, but
> seems a bit ugly since it's somewhat larger than most inline functions,
> and it would just bring that problem into the callers. Splitting the
> function into a separate file might be an alternative.
> This uses the big hammer by making CONFIG_NVMEM itself a 'bool' symbol,
> which avoids the problem entirely but makes the vmlinux larger for anyone
> that might use NVMEM support but doesn't need it built-in otherwise.
> Fixes: 9217e566bdee ("of_net: Implement of_get_nvmem_mac_address helper")
> Cc: Mike Looijmans <>
> Cc: Florian Fainelli <>
> Cc: Andrew Lunn <>
> Cc: David S. Miller <>
> Cc:
> Signed-off-by: Arnd Bergmann <>
> ---
> The problem arrived through the networking tree, but it's now in
> mainline, so the fix could go through either tree
> ---
> drivers/nvmem/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
> index 5f9bc787d634..1090924efdb1 100644
> --- a/drivers/nvmem/Kconfig
> +++ b/drivers/nvmem/Kconfig
> @@ -1,5 +1,5 @@
> menuconfig NVMEM
> - tristate "NVMEM Support"
> + bool "NVMEM Support"
> help
> Support for NVMEM(Non Volatile Memory) devices like EEPROM, EFUSES...

Kind regards,

Mike Looijmans
System Expert

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