cxl: Add HDM-DB region creation

A region created through sysfs inherits its coherency from the chosen
root decoder - HDM-DB if the root has CXL_DECODER_F_BI, otherwise
HDM-H. An auto-assembled region takes its type from the committed
decoder it is built from instead.

cxl_acpi_cfmws_verify() rejects a Window that declares no coherency
model at all (neither Device Coherent nor Host-only Coherent), and one
that sets BI together with Host-only Coherent, which the CFMWS
definition calls undefined behavior. A BI Window therefore always
exposes device-coherent memory and nothing else, HDM-DB being defined
only as bit[0] and bit[5] together.

Introduce the following read-only sysfs ABI.

  - decoderX.Y/cap_back_invalidate (root) reports the CFMWS BI
    restriction.
  - decoderX.Y/back_invalidate (endpoint) reads '1' when configured
    for HDM-DB.

cxl_region_attach() rejects endpoints whose device or HDM cannot
serve the region's type; target_type is inherited from cxlr->type
in cxl_rr_assign_decoder(), restored to the endpoint default on
detach unless the decoder is still committed, and to whatever it was
on a failed attach - a refusal may come before any inheritance, for a
decoder another region owns or one firmware committed, and must not
relabel it.

An HDM that reports Unknown coherency support is not rejected.
Supported Coherency Models is how a device declares whether Target
Range Type is writable - Host-only+Device Coherent means RW, a single
model means the bit may be hardwired to it, Unknown declares neither
- so refusing Unknown would also exclude devices that support both
models without saying so.

A Type 3 decoder defaults to host-only, unless its HDM supports only
device-coherent, and inherits device-coherent when it joins an HDM-DB
region, which requires cxlds->bi. A Type 2 decoder defaults to
device-coherent and an HDM-H region refuses it outright, since the
spec reserves HDM-H for Type 3 devices. An HDM-D region is only
assembled from a committed decoder, taking that decoder's type, so no
inheritance is involved.

The HDM Decoder Control BI bit is set at commit time for a
device-coherent decoder in a region under a BI root, endpoint and
switch decoders alike. Whether the device has BI enabled (cxlds->bi)
is checked when an endpoint attaches and again for every target
before a commit programs anything, since a reset in between
invalidates it; the refusal is the same in both places.

The BI bit a decoder was committed with is read back and recorded as
CXL_DECODER_F_BI, and cleared with CXL_DECODER_F_ENABLE on reset. On
a root decoder the same flag is the window's BI restriction, as
F_LOCK already means a fixed window there and Lock On Commit below.

A committed decoder cannot inherit a region's type, so its range type
is checked instead: against the window before the region is built,
as the manual path already does through can_create_ram(), and
against the region at attach, where upstream's type mismatch refusal
stays for committed decoders. Committed means CXL_DECODER_F_ENABLE,
not an auto-assembly state: a decoder left committed by a region that
never assembled, or by a locked one, is as committed as one in an
assembled region.

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Link: https://patch.msgid.link/5d3ac10113c01cb52f12184b06eb6a1dcbb2516d.1794172701.git.dave@stgolabs.net
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

0 files changed, 0 insertions, 0 deletions