https://bugzilla.kernel.org/show_bug.cgi?id=203921
Bug ID: 203921
Summary: [Proposal] Expose contents of FPDT through sysfs
Product: ACPI
Version: 2.5
Kernel Version: 5.1
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Config-Tables
Assignee: acpi_config-tab...@kernel-bugs.osdl.org
Reporter: joe.ko...@linux.intel.com
Regression: No
Proposal: add sysfs nodes for retrieving information contained in ACPI
'Firmware Basic Boot Performance Data Record' as well as 'S3 Performance
Table'. This will provide performance tools-- like systemd or pm-graph-- with a
common interface to access the information contained in these ACPI tables.
Backing up: The Firmware Performance Data Table (FPDT) is documented in the
ACPI Spec v6.3[1] on page 209 (Section 5.2.23). The Spec records two "record
types" for FPDT: 'Firmware Basic Boot Performance Pointer Record' and 'S3
Performance Table Pointer Record'. Mind that these are "pointer" records,
meaning it's a layer of indirection-- the actual data is stored in other
tables.
Today, as of kernel v5.1, the platform's ACPI FPDT (if it exists) is exposed in
sysfs under:
/sys/firmware/acpi/tables/FPDT
However, retrieval of the actual Firmware Boot and S3 data is left as an
exercise to the user: e.g. systemd[2], pm-graph, or other like tools. The
tool/user has to roll their own method for getting at the actual information,
often requiring a trip into /dev/mem.
[1] ACPI v6.3 Spec:
https://uefi.org/sites/default/files/resources/ACPI_6_3_final_Jan30.pdf
[2] Example: how systemd gets at FPDT:
https://github.com/systemd/systemd/blob/1e5d2d656420d0e755dbcf72aeba3c3aba54e956/src/shared/acpi-fpdt.c#L64
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