netdev - Re: [PATCH net-next V2] net: ks8851: Fix mixed module/builtin build

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Date:   Sat, 16 Jan 2021 22:41:37 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Marek Vasut <marex@...x.de>, Lukas Wunner <lukas@...ner.de>,
        Arnd Bergmann <arnd@...nel.org>
Cc:     Networking <netdev@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next V2] net: ks8851: Fix mixed module/builtin build

On 16.01.2021 22:25, Marek Vasut wrote:
> On 1/16/21 9:39 PM, Lukas Wunner wrote:
>> On Sat, Jan 16, 2021 at 08:26:22PM +0100, Arnd Bergmann wrote:
>>> On Sat, Jan 16, 2021 at 6:56 PM Marek Vasut <marex@...x.de> wrote:
>>>> On 1/16/21 6:04 PM, Arnd Bergmann wrote:
>>>>> On Sat, Jan 16, 2021 at 5:48 PM Marek Vasut <marex@...x.de> wrote:
>>>>
>>>>> I don't really like this version, as it does not actually solve the problem of
>>>>> linking the same object file into both vmlinux and a loadable module, which
>>>>> can have all kinds of side-effects besides that link failure you saw.
>>>>>
>>>>> If you want to avoid exporting all those symbols, a simpler hack would
>>>>> be to '#include "ks8851_common.c" from each of the two files, which
>>>>> then always duplicates the contents (even when both are built-in), but
>>>>> at least builds the file the correct way.
>>>>
>>>> That's the same as V1, isn't it ?
>>>
>>> Ah, I had not actually looked at the original submission, but yes, that
>>> was slightly better than v2, provided you make all symbols static to
>>> avoid the new link error.
>>>
>>> I still think that having three modules and exporting the symbols from
>>> the common part as Heiner Kallweit suggested would be the best
>>> way to do it.
>>
>> FWIW I'd prefer V1 (the #include approach) as it allows going back to
>> using static inlines for register access.  That's what we had before
>> 7a552c850c45.
>>
>> It seems unlikely that a system uses both, the parallel *and* the SPI
>> variant of the ks8851.  So the additional memory necessary because of
>> code duplication wouldn't matter in practice.
> 
> I have a board with both options populated on my desk, sorry.

Making the common part a separate module shouldn't be that hard.
AFAICS it would just take:
- export 4 functions from common
- extend Kconfig
- extend Makefile
One similar configuration that comes to my mind and could be used as
template is SPI_FSL_LIB.