ntb: reduce stack usage in idt_scan_mws

idt_scan_mws() puts a large fixed-size array on the stack and copies
it into a smaller dynamically allocated array at the end. On 32-bit
targets, the fixed size can easily exceed the warning limit for
possible stack overflow:

drivers/ntb/hw/idt/ntb_hw_idt.c:1041:27: error: stack frame size (1032) exceeds limit (1024) in 'idt_scan_mws' [-Werror,-Wframe-larger-than]

Change it to instead just always use dynamic allocation for the
array from the start. It's too big for the stack, but not actually
all that much for a permanent allocation.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/all/202205111109.PiKTruEj-lkp@intel.com/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

Author: arndb

drivers/ntb/hw/idt/ntb_hw_idt.c

@@ -1041,14 +1041,19 @@ static inline char *idt_get_mw_name(enum idt_mw_type mw_type)
 static struct idt_mw_cfg *idt_scan_mws(struct idt_ntb_dev *ndev, int port,
 				       unsigned char *mw_cnt)
 {
-	struct idt_mw_cfg mws[IDT_MAX_NR_MWS], *ret_mws;
+	struct idt_mw_cfg *mws;
 	const struct idt_ntb_bar *bars;
 	enum idt_mw_type mw_type;
 	unsigned char widx, bidx, en_cnt;
 	bool bar_64bit = false;
 	int aprt_size;
 	u32 data;
 
+	mws = devm_kcalloc(&ndev->ntb.pdev->dev, IDT_MAX_NR_MWS,
+			   sizeof(*mws), GFP_KERNEL);
+	if (!mws)
+		return ERR_PTR(-ENOMEM);
+
 	/* Retrieve the array of the BARs registers */
 	bars = portdata_tbl[port].bars;
 
@@ -1103,16 +1108,7 @@ static struct idt_mw_cfg *idt_scan_mws(struct idt_ntb_dev *ndev, int port,
 		}
 	}
 
-	/* Allocate memory for memory window descriptors */
-	ret_mws = devm_kcalloc(&ndev->ntb.pdev->dev, *mw_cnt, sizeof(*ret_mws),
-			       GFP_KERNEL);
-	if (!ret_mws)
-		return ERR_PTR(-ENOMEM);
-
-	/* Copy the info of detected memory windows */
-	memcpy(ret_mws, mws, (*mw_cnt)*sizeof(*ret_mws));
-
-	return ret_mws;
+	return mws;
 }
 
 /*