cxl/acpi: Warn on mixed CXL VH and RCH/RCD Hierarchy
Each Host Bridge instance has a corresponding CXL Host Bridge Structure
(CHBS) ACPI table that identifies its capabilities. CHBS tables can be
two types (CXL 3.1 Table 9-21): The PCIe Root Complex Register Block
(RCRB) and CXL Host Bridge Component Registers (CHBCR).
If a Host Bridge is attached to a device that is operating in Restricted
CXL Device Mode (RCD), BIOS publishes an RCRB with the base address of
registers that describe its capabilities (CXL 3.1 sec. 9.11).
Instead, the new (CXL 2.0+) Component registers can only be accessed
by means of a base address published with a CHBCR (CXL 3.1 sec. 9.12).
If an eRCD (a device that forces the host-bridge into CXL 1.1 Restricted
CXL Host mode) is attached to a CXL 2.0+ Host-Bridge, the current CXL
specification does not define a mechanism for finding CXL-2.0-only
root-port component registers like HDM decoders and Extended Security
capability.
An algorithm to locate a CHBCR associated with an RCRB, would be too
invasive to land without some concrete motivation.
Therefore, just print a message to inform of unsupported config.
Count how many different CHBS "Version" types are detected by
cxl_get_chbs_iter(). Then make cxl_get_chbs() print a warning if that sum
is greater than 1.
Tested-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://patch.msgid.link/20240628175535.272472-1-fabio.m.de.francesco@linux.intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
1 file changed
