dma-mapping: fix missing clear bdr in check_ram_in_range_map()

As discussed in [1], if 'bdr' is set once, it would never get
cleared, hence 0 is always returned.

Refactor the range check hunk into a new helper dma_find_range(),
which allows 'bdr' to be cleared in each iteration.

Link: https://lore.kernel.org/all/64931fac-085b-4ff3-9314-84bac2fa9bdb@quicinc.com/ # [1]
Fixes: a409d96 ("dma-mapping: fix dma_addressing_limited() if dma_range_map can't cover all system RAM")
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Link: https://lore.kernel.org/r/20250307030350.69144-1-quic_bqiang@quicinc.com
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

Author: Baochen Qiang

kernel/dma/direct.c

@@ -584,6 +584,22 @@ int dma_direct_supported(struct device *dev, u64 mask)
 	return mask >= phys_to_dma_unencrypted(dev, min_mask);
 }
 
+static const struct bus_dma_region *dma_find_range(struct device *dev,
+						   unsigned long start_pfn)
+{
+	const struct bus_dma_region *m;
+
+	for (m = dev->dma_range_map; PFN_DOWN(m->size); m++) {
+		unsigned long cpu_start_pfn = PFN_DOWN(m->cpu_start);
+
+		if (start_pfn >= cpu_start_pfn &&
+		    start_pfn - cpu_start_pfn < PFN_DOWN(m->size))
+			return m;
+	}
+
+	return NULL;
+}
+
 /*
  * To check whether all ram resource ranges are covered by dma range map
  * Returns 0 when further check is needed
@@ -593,20 +609,12 @@ static int check_ram_in_range_map(unsigned long start_pfn,
 				  unsigned long nr_pages, void *data)
 {
 	unsigned long end_pfn = start_pfn + nr_pages;
-	const struct bus_dma_region *bdr = NULL;
-	const struct bus_dma_region *m;
 	struct device *dev = data;
 
 	while (start_pfn < end_pfn) {
-		for (m = dev->dma_range_map; PFN_DOWN(m->size); m++) {
-			unsigned long cpu_start_pfn = PFN_DOWN(m->cpu_start);
+		const struct bus_dma_region *bdr;
 
-			if (start_pfn >= cpu_start_pfn &&
-			    start_pfn - cpu_start_pfn < PFN_DOWN(m->size)) {
-				bdr = m;
-				break;
-			}
-		}
+		bdr = dma_find_range(dev, start_pfn);
 		if (!bdr)
 			return 1;