nvmem: disallow modular CONFIG_NVMEM

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 <[email protected]>
Cc: Florian Fainelli <[email protected]>
Cc: Andrew Lunn <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: [email protected]
Signed-off-by: Arnd Bergmann <[email protected]>
Acked-by: Mike Looijmans
Signed-off-by: David S. Miller <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index ff505af064ba..55cf64ee7f7b 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...