EINJ, Documentation: Update EINJ kernel doc

Update EINJ kernel document to include how to inject CXL protocol error
types, build the kernel to include CXL error types, and give an example
injection.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Ben Cheatham <Benjamin.Cheatham@amd.com>
Link: https://lore.kernel.org/r/20240311142508.31717-5-Benjamin.Cheatham@amd.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/firmware-guide/acpi/apei/einj.rst

@@ -32,6 +32,10 @@ configuration::
   CONFIG_ACPI_APEI
   CONFIG_ACPI_APEI_EINJ
 
+...and to (optionally) enable CXL protocol error injection set::
+
+  CONFIG_ACPI_APEI_EINJ_CXL
+
 The EINJ user interface is in <debugfs mount point>/apei/einj.
 
 The following files belong to it:
@@ -118,6 +122,24 @@ The following files belong to it:
   this actually works depends on what operations the BIOS actually
   includes in the trigger phase.
 
+CXL error types are supported from ACPI 6.5 onwards (given a CXL port
+is present). The EINJ user interface for CXL error types is at
+<debugfs mount point>/cxl. The following files belong to it:
+
+- einj_types:
+
+  Provides the same functionality as available_error_types above, but
+  for CXL error types
+
+- $dport_dev/einj_inject:
+
+  Injects a CXL error type into the CXL port represented by $dport_dev,
+  where $dport_dev is the name of the CXL port (usually a PCIe device name).
+  Error injections targeting a CXL 2.0+ port can use the legacy interface
+  under <debugfs mount point>/apei/einj, while CXL 1.1/1.0 port injections
+  must use this file.
+
+
 BIOS versions based on the ACPI 4.0 specification have limited options
 in controlling where the errors are injected. Your BIOS may support an
 extension (enabled with the param_extension=1 module parameter, or boot
@@ -181,6 +203,18 @@ You should see something like this in dmesg::
   [22715.834759] EDAC sbridge MC3: PROCESSOR 0:306e7 TIME 1422553404 SOCKET 0 APIC 0
   [22716.616173] EDAC MC3: 1 CE memory read error on CPU_SrcID#0_Channel#0_DIMM#0 (channel:0 slot:0 page:0x12345 offset:0x0 grain:32 syndrome:0x0 -  area:DRAM err_code:0001:0090 socket:0 channel_mask:1 rank:0)
 
+A CXL error injection example with $dport_dev=0000:e0:01.1::
+
+    # cd /sys/kernel/debug/cxl/
+    # ls
+    0000:e0:01.1 0000:0c:00.0
+    # cat einj_types                # See which errors can be injected
+	0x00008000  CXL.mem Protocol Correctable
+	0x00010000  CXL.mem Protocol Uncorrectable non-fatal
+	0x00020000  CXL.mem Protocol Uncorrectable fatal
+    # cd 0000:e0:01.1               # Navigate to dport to inject into
+    # echo 0x8000 > einj_inject     # Inject error
+
 Special notes for injection into SGX enclaves:
 
 There may be a separate BIOS setup option to enable SGX injection.