linux-kernel - Re: [PATCH v2 1/2] mips: cm: Convert __mips_cm_l2sync_phys

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Message-Id: <cc9e02b3-57df-4a7d-bd21-2d574bf4b878@app.fastmail.com>
Date: Mon, 26 Feb 2024 13:04:33 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Serge Semin" <fancer.lancer@...il.com>
Cc: "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "Jiaxun Yang" <jiaxun.yang@...goat.com>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Alexey Malahov" <Alexey.Malahov@...kalelectronics.ru>,
 linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mips: cm: Convert __mips_cm_l2sync_phys_base() to weak
 function

On Mon, Feb 26, 2024, at 12:27, Serge Semin wrote:
> On Mon, Feb 26, 2024 at 12:04:06PM +0100, Arnd Bergmann wrote:
>> On Mon, Feb 26, 2024, at 11:54, Serge Semin wrote:
s to.
>> 
>> Since the resolution of the alias is all done at link time
>> anyway, could you just convert these to an #ifdef check
>> that documents exactly when each of the versions is used?
>
> Not sure I've completely understood what you meant. Do you suggest to
> add a mips_cm_l2sync_phys_base macro which would be defined if a
> "strong" version of the method is defined (and surround the
> underscored function by it)?
>
> Please note after this patch is applied no aliases will
> be left, but only a single weakly defined method:
> mips_cm_l2sync_phys_base()
> This is what we agreed to do with Thomas:
> https://lore.kernel.org/linux-mips/pf6cvzper4g5364nqhd4wd2pmlkyygoymobeqduulpslcjhyy6@kf66z7chjbl3
> Thus there will be no need in the macro you suggest since the
> weak-version of the method will be discarded by the linker as it will
> have been replaced with the "strong" one. 

I meant that instead of having both a weak and an optional strong
version that get linked together, always define exactly one of the
two, such as:

#ifndef CONFIG_MIPS_CM_xxx
static phys_addr_t mips_cm_l2sync_phys_base(void)
{
       /* current implementation ... */
}
#endif

where CONFIG_MIPS_CM_xxx is the Kconfig symbol that decides
whether the file with the strong version is built or not.

This way you always get exactly one of the two versions
of the function built, the local version can be inlined
if the compiler thinks that is better, and the #ifdef
documents exactly whether the function is used or not
for a given configuration, rather than a reader having
to track down how many other definitions exist and whether
a config includes them.

       Arnd