linux-kernel - Re: [PATCH] clk: ralink: mtmips: quiet unused variable warning

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Message-Id: <b0e203e7-3b3c-40ad-8d99-e43415c0d3c5@app.fastmail.com>
Date:   Thu, 03 Aug 2023 09:58:34 +0200
From:   "Arnd Bergmann" <arnd@...nel.org>
To:     "Sergio Paracuellos" <sergio.paracuellos@...il.com>
Cc:     "Michael Turquette" <mturquette@...libre.com>,
        "Nathan Chancellor" <nathan@...nel.org>,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Stephen Boyd" <sboyd@...nel.org>,
        "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
        clang-built-linux <llvm@...ts.linux.dev>,
        "kernel test robot" <lkp@...el.com>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: ralink: mtmips: quiet unused variable warning

On Thu, Aug 3, 2023, at 00:35, Sergio Paracuellos wrote:
> Hi Arnd. 
>
> El El jue, 3 ago 2023 a las 0:02, Arnd Bergmann <arnd@...nel.org> escribió:
>> On Wed, Aug 2, 2023, at 23:26, Nick Desaulniers wrote:
>> > On Wed, Aug 2, 2023 at 2:26 AM Sergio Paracuellos <sergio.paracuellos@...il.com> wrote:
>> >>
>> >> When CONFIG_OF is disabled then the matching table is not referenced and
>> >> the following warning appears:
>> >>
>> >> drivers/clk/ralink/clk-mtmips.c:821:34: warning: unused variable 'mtmips_of_match' [-Wunused-const-variable]
>> >> 821 |   static const struct of_device_id mtmips_of_match[] = {
>> >>     |                          ^
>> >>
>> >> Silence it declaring 'mtmips_of_match' with '__maybe_unused'.
>> >>
>> >> Fixes: 6f3b15586eef ("clk: ralink: add clock and reset driver for MTMIPS SoCs")
>> >> Reported-by: kernel test robot <lkp@...el.com>
>> >> Closes: https://lore.kernel.org/oe-kbuild-all/202307242310.CdOnd2py-lkp@intel.com/
>> >> Signed-off-by: Sergio Paracuellos <sergio.paracuellos@...il.com>
>> >
>> > I think this is fine; Arnd or Nathan do you have a preference? or thoughts here?
>> >
>> > If not, thanks for the patch.
>> > Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
>> >
>> > (I have a slight preference for wrapping the use in `#ifdef CONFIG_OF`
>> > since with the approach used by this patch, if all users are removed
>> > we will never get a warning for this var. But it's a weak preference;
>> > it's more important to me that we don't have -Werror promote this
>> > warning to a build breakage)
>> 
>> I don't understand why there are two match tables in the same
>> driver, with almost the same contents. I have not looked very
>> closely here, but why can't we just drop the mtmips_clk_of_match[]
>> table (the one without the .data fields) and use the same
>> table for both? Is this because of the ralink,rt2880-reset entry
>> that is missing in mtmips_of_match, or is that another bug?
>
> ralink,rt2880-reset is for old dts compatibility and only applies to 
> reset driver. The one with data fields apply for clocks and is needed.

Ok, I see. It still looks like the two tables can simply be
merged by adding the ralink,rt2880-reset entry to mtmips_of_match[],
which will allow it to be used for mtmips_clk_driver (which doesn't
use the data) as well as for mtmips_clk_init() (which doesn't
need get called for ralink,rt2880-reset).

>> I also see that there is both a platform_driver instance for
>> late probing and a list of CLK_OF_DECLARE_DRIVER() entries.
>> Do we need both here?
>
> This system controller driver provide clock and reset controllers. 
> Clock cannot be a platform driver since we need to set 
> mips_hpr_frequency at a very early sargento. Reset stuff can be a 
> platform driver so both of them are needed.

     Arnd