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Tables: Back port acpi_get_table_with_size() and early_acpi_os_unmap_…
…memory() from Linux kernel This patch back ports Linux acpi_get_table_with_size() and early_acpi_os_unmap_memory() into ACPICA upstream. 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 reference counting based style: 1. When the reference of the table is increased from 0 to 1, table is mapped and .Pointer is set with the mapping address (VALIDATED); 2. When the reference 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 replacing acpi_get_table_with_size() with acpi_get_table() and replacing early_acpi_os_unmap_memory() with acpi_put_table(). Note that ACPI_TABLE_IS_INVALIDATED is introduced in this patch to increase the table reference count when the table is internal validated. Lv Zheng. Signed-off-by: Lv Zheng <lv.zheng@intel.com>
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Lv Zheng
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Feb 26, 2016
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