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    ACPICA: Tables: Back port acpi_get_table_with_size() and... · 174cc718
    Lv Zheng 提交于
    ACPICA: Tables: Back port acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux kernel
    
    ACPICA commit cac6790954d4d752a083e6122220b8a22febcd07
    
    This patch back ports Linux acpi_get_table_with_size() and
    early_acpi_os_unmap_memory() into ACPICA upstream to reduce divergences.
    
    The 2 APIs are used by Linux as table management APIs for long time, it
    contains a hidden logic that during the early stage, the mapped tables
    should be unmapped before the early stage ends.
    
    During the early stage, tables are handled by the following sequence:
     acpi_get_table_with_size();
     parse the table
     early_acpi_os_unmap_memory();
    During the late stage, tables are handled by the following sequence:
     acpi_get_table();
     parse the table
    Linux uses acpi_gbl_permanent_mmap to distinguish the early stage and the
    late stage.
    
    The reasoning of introducing acpi_get_table_with_size() is: ACPICA will
    remember the early mapped pointer in acpi_get_table() and Linux isn't able to
    prevent ACPICA from using the wrong early mapped pointer during the late
    stage as there is no API provided from ACPICA to be an inverse of
    acpi_get_table() to forget the early mapped pointer.
    
    But how ACPICA can work with the early/late stage requirement? Inside of
    ACPICA, tables are ensured to be remained in "INSTALLED" state during the
    early stage, and they are carefully not transitioned to "VALIDATED" state
    until the late stage. So the same logic is in fact implemented inside of
    ACPICA in a different way. The gap is only that the feature is not provided
    to the OSPMs in an accessible external API style.
    
    It then is possible to fix the gap by providing an inverse of
    acpi_get_table() from ACPICA, so that the two Linux sequences can be
    combined:
     acpi_get_table();
     parse the table
     acpi_put_table();
    In order to work easier with the current Linux code, acpi_get_table() and
    acpi_put_table() is implemented in a usage counting based style:
     1. When the usage count of the table is increased from 0 to 1, table is
        mapped and .Pointer is set with the mapping address (VALIDATED);
     2. When the usage count of the table is decreased from 1 to 0, .Pointer
        is unset and the mapping address is unmapped (INVALIDATED).
    So that we can deploy the new APIs to Linux with minimal effort by just
    invoking acpi_get_table() in acpi_get_table_with_size() and invoking
    acpi_put_table() in early_acpi_os_unmap_memory(). Lv Zheng.
    
    Link: https://github.com/acpica/acpica/commit/cac67909Signed-off-by: NLv Zheng <lv.zheng@intel.com>
    Signed-off-by: NBob Moore <robert.moore@intel.com>
    Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
    174cc718
actbl.h 19.4 KB