cxl/region: Avoid duplicate call of cxl_port_pick_region_decoder()

Function cxl_port_pick_region_decoder() is called twice, in
alloc_region_ref() and cxl_rr_alloc_decoder(). Both functions are
subsequently called from cxl_port_attach_region(). Make the decoder a
function argument to both which avoids a duplicate call of
cxl_port_pick_region_decoder().

Now, cxl_rr_alloc_decoder() no longer allocates the decoder. Instead,
the previously picked decoder is assigned to the region reference.
Hence, rename the function to cxl_rr_assign_decoder().

Moving the call out of alloc_region_ref() also moves it out of the
xa_for_each() loop in there. Now, cxld is determined no longer only
for each auto-generated region, but now once for all regions
regardless of auto-generated or not. This is fine as the cxld argument
is needed for all regions in cxl_rr_assign_decoder() and an error would
be returned otherwise anyway. So it is better to determine the decoder
in front of all this and fail early if missing instead of running
through all that code with multiple calls of
cxl_port_pick_region_decoder().

Signed-off-by: Robert Richter <rrichter@amd.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: "Fabio M. De Francesco" <fabio.m.de.francesco@linux.intel.com>
Tested-by: Gregory Price <gourry@gourry.net>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Link: https://patch.msgid.link/20250509150700.2817697-7-rrichter@amd.com


Signed-off-by: Dave Jiang <dave.jiang@intel.com>