linux-kernel - Re: [PATCH] [net] nvmem: disallow modular CONFIG

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Date:   Wed, 4 Apr 2018 15:32:43 +0200
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     Arnd Bergmann <arnd@...db.de>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
CC:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [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 
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 <mike.looijmans@...ic.nl>
> Cc: Florian Fainelli <f.fainelli@...il.com>
> Cc: Andrew Lunn <andrew@...n.ch>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> 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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