Re: [PATCH] [net] nvmem: disallow modular CONFIG_NVMEM

[David Miller]

From: Arnd Bergmann 
Date: Wed,  4 Apr 2018 12:38:40 +0200

> 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: netdev@vger.kernel.org
> 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

Ok, applied, thanks Arnd.

Re: [PATCH] [net] nvmem: disallow modular CONFIG_NVMEM

[Arnd Bergmann]

On Wed, Apr 4, 2018 at 3:32 PM, Mike Looijmans  wrote:

>
> 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?

Right, it would require having a

  depends on NVMEM || !NVMEM

line in Kconfig for each such driver, or a

  depends on NVMEM != m

for drivers that cannot be modules themselves.

  Arnd

Re: [PATCH] [net] nvmem: disallow modular CONFIG_NVMEM

[Mike Looijmans]

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 
any.



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?


--
Mike.


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: netdev@vger.kernel.org
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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