cxl: Add handling of locked CXL decoder

When a decoder is locked, it means that its configuration cannot be
changed. CXL spec r3.2 8.2.4.20.13 discusses the details regarding
locked decoders. Locking happens when bit 8 of the decoder control
register is set and then the decoder is committed afterwards (CXL
spec r3.2 8.2.4.20.7).

Given that the driver creates a virtual decoder for each CFMWS, the
Fixed Device Configuration (bit 4) of the Window Restriction field is
considered as locking for the virtual decoder by the driver.

The current driver code disregards the locked status and a region can
be destroyed regardless of the locking state.

Add a region flag to indicate the region is in a locked configuration.
The driver will considered a region locked if the CFMWS or any decoder
is configured as locked. The consideration is all or nothing regarding
the locked state. It is reasonable to determine the region "locked"
status while the region is being assembled based on the decoders.

Add a check in region commit_store() to intercept when a 0 is written
to the commit sysfs attribute in order to prevent the destruction of a
region when in locked state. This should be the only entry point from user
space to destroy a region.

Add a check is added to cxl_decoder_reset() to prevent resetting a locked
decoder within the kernel driver.

Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20251105201826.2901915-1-dave.jiang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

0 files changed, 0 insertions, 0 deletions