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The /proc/self/auxv contains information about "platform" on any system. Also "base platform" which is an indication about platform string corresponding to the real PVR. When systems are booted in compat mode, say, power10 booted in power9 mode, "platform" will point to power9 whereas base platform will point to power10. Incase, if the distro doesn't support platform indicated by real PVR, base platform will have a default value. The mismatch of platform/base platform is an indication of system booted in compat mode. In such cases, distro will have a Generic Compat registered which supports basic features for performance monitoring. Some of the selftest needs to be handled differently ( ex: generic events, alternative events, bhrb filter map) in Generic Compat PMU. Hence selftest framework needs utility functions to identify such cases. One way is make sure of auxv information. Below condition can be used to detect if Generic Compat PMU is registered. ie: if ((AT_PLATFORM != AT_BASE_PLATFORM) && (AT_BASE_PLATFORM != PVR)) this indicates Generic Compat PMU. Add utility function in "include/utils.h" to return: AT_PLATFORM and AT_BASE_PLATFORM from auxv. Also update misc.c in "sampling_tests" folder to add function to use above check to determine presence of generic compat pmu. In other architecture ( like x86 ), pmu_name is exposed via "/sys/bus/event_source/devices/cpu/caps". The same could be used in powerpc in future. Since currently we don't have the "caps" support in powerpc, patch uses auxv information to detect platform type and compat mode. But as placeholder utility function is added considering possiblity of getting "caps" information via sysfs. If that doesn't exist, fallback to using auxv information. Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20220610134113.62991-3-atrajeev@linux.vnet.ibm.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.