cxl/core: Remove cxld_const_init in cxl_decoder_alloc()

Commit 48667f6 ("cxl/core: Split decoder setup into alloc + add")
aimed to fix a large stack frame warning but from v5 to v6, it
introduced a new instance of the warning due to allocating
cxld_const_init on the stack, which was done due to the use of const on
the nr_target member of the cxl_decoder struct. With ARCH=arm
allmodconfig minus CONFIG_KASAN:

GCC 11.2.0:

drivers/cxl/core/bus.c: In function ‘cxl_decoder_alloc’:
drivers/cxl/core/bus.c:523:1: error: the frame size of 1032 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
  523 | }
      | ^
cc1: all warnings being treated as errors

Clang 12.0.1:

drivers/cxl/core/bus.c:486:21: error: stack frame size of 1056 bytes in function 'cxl_decoder_alloc' [-Werror,-Wframe-larger-than=]
struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port, int nr_targets)
                    ^
1 error generated.

Revert that part of the change, which makes the stack frame of
cxl_decoder_alloc() much more reasonable.

Fixes: 48667f6 ("cxl/core: Split decoder setup into alloc + add")
Link: ClangBuiltLinux#1539
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20211210213627.2477370-1-nathan@kernel.org
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Author: nathanchance

drivers/cxl/core/bus.c

@@ -485,9 +485,7 @@ static int decoder_populate_targets(struct cxl_decoder *cxld,
 
 struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port, int nr_targets)
 {
-	struct cxl_decoder *cxld, cxld_const_init = {
-		.nr_targets = nr_targets,
-	};
+	struct cxl_decoder *cxld;
 	struct device *dev;
 	int rc = 0;
 
@@ -497,13 +495,13 @@ struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port, int nr_targets)
 	cxld = kzalloc(struct_size(cxld, target, nr_targets), GFP_KERNEL);
 	if (!cxld)
 		return ERR_PTR(-ENOMEM);
-	memcpy(cxld, &cxld_const_init, sizeof(cxld_const_init));
 
 	rc = ida_alloc(&port->decoder_ida, GFP_KERNEL);
 	if (rc < 0)
 		goto err;
 
 	cxld->id = rc;
+	cxld->nr_targets = nr_targets;
 	dev = &cxld->dev;
 	device_initialize(dev);
 	device_set_pm_not_required(dev);

drivers/cxl/cxl.h

@@ -191,7 +191,7 @@ struct cxl_decoder {
 	int interleave_granularity;
 	enum cxl_decoder_type target_type;
 	unsigned long flags;
-	const int nr_targets;
+	int nr_targets;
 	struct cxl_dport *target[];
 };