• Srinivas Pandruvada's avatar
    ACPI / LPIT: Add Low Power Idle Table (LPIT) support · eeb2d80d
    Srinivas Pandruvada authored
    Add functionality to read LPIT table, which provides:
    
     - Sysfs interface to read residency counters via
       /sys/devices/system/cpu/cpuidle/low_power_idle_cpu_residency_us
       /sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us
    
    Here the count "low_power_idle_cpu_residency_us" shows the time spent
    by CPU package in low power state.  This is read via MSR interface,
    which points to MSR for PKG C10.
    
    Here the count "low_power_idle_system_residency_us" show the count the
    system was in low power state. This is read via MMIO interface. This
    is mapped to SLP_S0 residency on modern Intel systems. This residency
    is achieved only when CPU is in PKG C10 and all functional blocks are
    in low power state.
    
    It is possible that none of the above counters present or anyone of the
    counter present or all counters present.
    
    For example: On my Kabylake system both of the above counters present.
    After suspend to idle these counts updated and prints:
    
     6916179
     6998564
    
    This counter can be read by tools like turbostat to display. Or it can
    be used to debug, if modern systems are reaching desired low power state.
    
     - Provides an interface to read residency counter memory address
    
       This address can be used to get the base address of PMC memory
       mapped IO.  This is utilized by intel_pmc_core driver to print
       more debug information.
    
    In addition, to avoid code duplication to read iomem, removed the read of
    iomem from acpi_os_read_memory() in osl.c and made a common function
    acpi_os_read_iomem(). This new function is used for reading iomem in
    in both osl.c and acpi_lpit.c.
    
    Link: http://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdfSigned-off-by: 's avatarSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
    Signed-off-by: 's avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    eeb2d80d
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