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77e2a04745
PCC OpRegion provides a mechanism to communicate with the platform
directly from the AML. PCCT provides the list of PCC channel available
in the platform, a subset or all of them can be used in PCC Opregion.
This patch registers the PCC OpRegion handler before ACPI tables are
loaded. This relies on the special context data passed to identify and
set up the PCC channel before the OpRegion handler is executed for the
first time.
Typical PCC Opregion declaration looks like this:
OperationRegion (PFRM, PCC, 2, 0x74)
Field (PFRM, ByteAcc, NoLock, Preserve)
{
SIGN, 32,
FLGS, 32,
LEN, 32,
CMD, 32,
DATA, 800
}
It contains four named double words followed by 100 bytes of buffer
names DATA.
ASL can fill out the buffer something like:
/* Create global or local buffer */
Name (BUFF, Buffer (0x0C){})
/* Create double word fields over the buffer */
CreateDWordField (BUFF, 0x0, WD0)
CreateDWordField (BUFF, 0x04, WD1)
CreateDWordField (BUFF, 0x08, WD2)
/* Fill the named fields */
WD0 = 0x50434300
SIGN = BUFF
WD0 = 1
FLGS = BUFF
WD0 = 0x10
LEN = BUFF
/* Fill the payload in the DATA buffer */
WD0 = 0
WD1 = 0x08
WD2 = 0
DATA = BUFF
/* Write to CMD field to trigger handler */
WD0 = 0x4404
CMD = BUFF
This buffer is received by acpi_pcc_opregion_space_handler. This
handler will fetch the complete buffer via internal_pcc_buffer.
The setup handler will receive the special PCC context data which will
contain the PCC channel index which used to set up the channel. The
buffer pointer and length is saved in region context which is then used
in the handler.
(kernel test robot: Build failure with CONFIG_ACPI_DEBUGGER)
Link: https://lore.kernel.org/r/202201041539.feAV0l27-lkp@intel.com
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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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.