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de66cb37ab
Many cpucaps can only be set when certain CONFIG_* options are selected,
and we need to check the CONFIG_* option before the cap in order to
avoid generating redundant code. Due to this, we have a growing number
of helpers in <asm/cpufeature.h> of the form:
| static __always_inline bool system_supports_foo(void)
| {
| return IS_ENABLED(CONFIG_ARM64_FOO) &&
| cpus_have_const_cap(ARM64_HAS_FOO);
| }
This is unfortunate as it forces us to use cpus_have_const_cap()
unnecessarily, resulting in redundant code being generated by the
compiler. In the vast majority of cases, we only require that feature
checks indicate the presence of a feature after cpucaps have been
finalized, and so it would be sufficient to use alternative_has_cap_*().
However some code needs to handle a feature before alternatives have
been patched, and must test the system_cpucaps bitmap via
cpus_have_const_cap(). In other cases we'd like to check for
unintentional usage of a cpucap before alternatives are patched, and so
it would be preferable to use cpus_have_final_cap().
Placing the IS_ENABLED() checks in each callsite is tedious and
error-prone, and the same applies for writing wrappers for each
comination of cpucap and alternative_has_cap_*() / cpus_have_cap() /
cpus_have_final_cap(). It would be nicer if we could centralize the
knowledge of which cpucaps are possible, and have
alternative_has_cap_*(), cpus_have_cap(), and cpus_have_final_cap()
handle this automatically.
This patch adds a new cpucap_is_possible() function which will be
responsible for checking the CONFIG_* option, and updates the low-level
cpucap checks to use this. The existing CONFIG_* checks in
<asm/cpufeature.h> are moved over to cpucap_is_possible(), but the (now
trival) wrapper functions are retained for now.
There should be no functional change as a result of this patch alone.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.