From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Lee Jones <lee.jones@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
Dominik Brodowski <linux@brodo.de>
Subject: Re: [PATCH 09/13] cpufreq: acpi-cpufreq: Remove unused ID structs
Date: Wed, 15 Jul 2020 14:11:24 +0200 [thread overview]
Message-ID: <CAJZ5v0jVvzCuxOa=xDXWw4Js0J5PfKb6aM4W-g=bAPz43JNqQg@mail.gmail.com> (raw)
In-Reply-To: <20200715120742.GD3165313@dell>
On Wed, Jul 15, 2020 at 2:07 PM Lee Jones <lee.jones@linaro.org> wrote:
>
> On Wed, 15 Jul 2020, Lee Jones wrote:
>
> > On Wed, 15 Jul 2020, Rafael J. Wysocki wrote:
> >
> > > On Wed, Jul 15, 2020 at 1:34 PM Lee Jones <lee.jones@linaro.org> wrote:
> > > >
> > > > On Wed, 15 Jul 2020, Rafael J. Wysocki wrote:
> > > >
> > > > > On Wed, Jul 15, 2020 at 5:27 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > > > > >
> > > > > > On 15-07-20, 08:54, Viresh Kumar wrote:
> > > > > > > On 14-07-20, 22:03, Lee Jones wrote:
> > > > > > > > On Tue, 14 Jul 2020, Rafael J. Wysocki wrote:
> > > > > > > >
> > > > > > > > > On Tue, Jul 14, 2020 at 4:51 PM Lee Jones <lee.jones@linaro.org> wrote:
> > > > > > > > > >
> > > > > > > > > > Can't see them being used anywhere and the compiler doesn't complain
> > > > > > > > > > that they're missing, so ...
> > > > > > > > >
> > > > > > > > > Aren't they needed for automatic module loading in certain configurations?
> > > > > > > >
> > > > > > > > Any idea how that works, or where the code is for that?
> > > > > > >
> > > > > > > The MODULE_DEVICE_TABLE() thingy creates a map of vendor-id,
> > > > > > > product-id that the kernel keeps after boot (and so there is no static
> > > > > > > reference of it for the compiler), later when a device is hotplugged
> > > > > > > into the kernel it refers to the map to find the related driver for it
> > > > > > > and loads it if it isn't already loaded.
> > > > > > >
> > > > > > > This has some of it, search for MODULE_DEVICE_TABLE() in it.
> > > > > > > Documentation/driver-api/usb/hotplug.rst
> > > > > >
> > > > > > And you just need to add __maybe_unused to them to suppress the
> > > > > > warning.
> > > > >
> > > > > Wouldn't that cause the compiler to optimize them away if it doesn't
> > > > > see any users?
> > > >
> > > > It looks like they're only unused when !MODULE,
> > >
> > > OK
> > >
> > > > in which case optimising them away would be the correct thing to do, no?
> >
> > It would be good if someone with a little more knowledge could provide
> > a second opinion though. I would think (hope) that the compiler would
> > be smart enough to see when its actually in use. After all, it is the
> > compiler that places the information into the device table.
> >
> > If that is not the case, then the MODULE_DEVICE_TABLE() magic is
> > broken and will need fixing. Removing boiler-plate is good, but not
> > at the expense of obfuscation.
>
> Okay, I'm satisfied. This test build is without __maybe_unused:
>
> # All configs built as modules (MODULE) - the compiler knows to use the tables
>
> $ ccache make -f Makefile -j24 KBUILD_OUTPUT=../builds/build-x86 allmodconfig
> $ ccache make -f Makefile -j24 KBUILD_OUTPUT=../builds/build-x86 W=1 drivers/cpufreq/
> [...]
> CC [M] drivers/cpufreq/pcc-cpufreq.o
>
> # All configs built-in (!MODULE) - the compiler sees that they are unused
>
> $ ccache make -f Makefile -j24 KBUILD_OUTPUT=../builds/build-x86 allyesconfig
> $ ccache make -f Makefile -j24 KBUILD_OUTPUT=../builds/build-x86 W=1 drivers/cpufreq/
> CC drivers/cpufreq/pcc-cpufreq.o
> drivers/cpufreq/pcc-cpufreq.c:619:36: warning: ‘processor_device_ids’ defined but not used [-Wunused-const-variable=]
> 619 | static const struct acpi_device_id processor_device_ids[] = {
> | ^~~~~~~~~~~~~~~~~~~~
>
OK
I thought that this would be the case. :-)
next prev parent reply other threads:[~2020-07-15 12:11 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-14 14:50 [PATCH 00/13] Rid W=1 warnings in CPUFreq Lee Jones
2020-07-14 14:50 ` [PATCH 01/13] cpufreq: freq_table: Demote obvious misuse of kerneldoc to standard comment blocks Lee Jones
2020-07-15 2:44 ` Viresh Kumar
2020-07-14 14:50 ` [PATCH 02/13] cpufreq: cpufreq: Demote lots of function headers unworthy of kerneldoc status Lee Jones
2020-07-15 2:49 ` Viresh Kumar
2020-07-15 6:47 ` Lee Jones
2020-07-15 7:09 ` Viresh Kumar
2020-07-14 14:50 ` [PATCH 03/13] cpufreq: cpufreq_governor: Demote store_sampling_rate() header to standard comment block Lee Jones
2020-07-15 2:52 ` Viresh Kumar
2020-07-15 6:45 ` Lee Jones
2020-07-15 7:08 ` Viresh Kumar
2020-07-15 7:31 ` Lee Jones
2020-07-15 8:02 ` Viresh Kumar
2020-07-15 8:15 ` Lee Jones
2020-07-14 14:50 ` [PATCH 04/13] cpufreq: sti-cpufreq: Fix some formatting and misspelling issues Lee Jones
2020-07-15 2:58 ` Viresh Kumar
2020-07-14 14:50 ` [PATCH 05/13] cpufreq/arch: powerpc: pasemi: Move prototypes to shared header Lee Jones
2020-07-15 3:07 ` Viresh Kumar
2020-07-15 3:49 ` Olof Johansson
2020-07-15 3:51 ` Viresh Kumar
2020-07-15 6:36 ` Lee Jones
2020-07-15 6:39 ` Viresh Kumar
2020-07-15 3:26 ` Olof Johansson
2020-07-15 6:33 ` Lee Jones
2020-07-15 6:46 ` Olof Johansson
2020-07-15 7:33 ` Lee Jones
2020-07-14 14:50 ` [PATCH 06/13] cpufreq: powernv-cpufreq: Functions only used in call-backs should be static Lee Jones
2020-07-15 3:07 ` Viresh Kumar
2020-07-14 14:50 ` [PATCH 07/13] cpufreq: powernv-cpufreq: Fix a bunch of kerneldoc related issues Lee Jones
2020-07-15 3:09 ` Viresh Kumar
2020-07-14 14:50 ` [PATCH 08/13] cpufreq: acpi-cpufreq: Take 'dummy' principle one stage further Lee Jones
2020-07-14 16:03 ` Rafael J. Wysocki
2020-07-14 16:20 ` Robin Murphy
2020-07-14 21:00 ` Lee Jones
2020-07-14 14:50 ` [PATCH 09/13] cpufreq: acpi-cpufreq: Remove unused ID structs Lee Jones
2020-07-14 15:58 ` Rafael J. Wysocki
2020-07-14 21:03 ` Lee Jones
2020-07-15 3:24 ` Viresh Kumar
2020-07-15 3:27 ` Viresh Kumar
2020-07-15 6:37 ` Lee Jones
2020-07-15 11:27 ` Rafael J. Wysocki
2020-07-15 11:34 ` Lee Jones
2020-07-15 11:44 ` Rafael J. Wysocki
2020-07-15 11:50 ` Lee Jones
2020-07-15 12:07 ` Lee Jones
2020-07-15 12:11 ` Rafael J. Wysocki [this message]
2020-07-15 12:09 ` Rafael J. Wysocki
2020-07-15 12:16 ` Lee Jones
2020-07-15 12:30 ` Robin Murphy
2020-07-15 12:38 ` Lee Jones
2020-07-14 14:50 ` [PATCH 10/13] cpufreq: powernow-k8: Make use of known set but not used variables Lee Jones
2020-07-14 17:43 ` Rafael J. Wysocki
2020-07-14 21:01 ` Lee Jones
2020-07-14 14:50 ` [PATCH 11/13] cpufreq: pcc-cpufreq: Remove unused ID structs Lee Jones
2020-07-14 17:42 ` Rafael J. Wysocki
2020-07-14 14:50 ` [PATCH 12/13] cpufreq: intel_pstate: Supply struct attribute description for get_aperf_mperf_shift() Lee Jones
2020-07-14 16:35 ` Rafael J. Wysocki
2020-07-14 21:03 ` Lee Jones
2020-07-15 12:38 ` Rafael J. Wysocki
2020-07-14 14:50 ` [PATCH 13/13] cpufreq: amd_freq_sensitivity: Remove unused ID structs Lee Jones
2020-07-14 17:15 ` Kim Phillips
2020-07-14 21:02 ` Lee Jones
2020-07-14 21:13 ` Kim Phillips
2020-07-15 6:47 ` Lee Jones
2020-07-15 3:36 ` [PATCH 00/13] Rid W=1 warnings in CPUFreq Viresh Kumar
2020-07-15 6:32 ` Lee Jones
2020-07-15 6:38 ` Viresh Kumar
2020-07-15 7:34 ` Lee Jones
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