net: airoha: Add the capability to allocate hwfd buffers via reserved-memory

In some configurations QDMA blocks require a contiguous block of
system memory for hwfd buffers queue. Introduce the capability to allocate
hw buffers forwarding queue via the reserved-memory DTS property instead of
running dmam_alloc_coherent().

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250521-airopha-desc-sram-v3-3-a6e9b085b4f0@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: LorenzoBianconi

drivers/net/ethernet/airoha/airoha_eth.c

@@ -5,6 +5,7 @@
  */
 #include <linux/of.h>
 #include <linux/of_net.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/platform_device.h>
 #include <linux/tcp.h>
 #include <linux/u64_stats_sync.h>
@@ -1072,20 +1073,46 @@ static void airoha_qdma_cleanup_tx_queue(struct airoha_queue *q)
 static int airoha_qdma_init_hfwd_queues(struct airoha_qdma *qdma)
 {
 	struct airoha_eth *eth = qdma->eth;
+	int id = qdma - &eth->qdma[0];
 	dma_addr_t dma_addr;
+	const char *name;
+	int size, index;
 	u32 status;
-	int size;
 
 	size = HW_DSCP_NUM * sizeof(struct airoha_qdma_fwd_desc);
 	if (!dmam_alloc_coherent(eth->dev, size, &dma_addr, GFP_KERNEL))
 		return -ENOMEM;
 
 	airoha_qdma_wr(qdma, REG_FWD_DSCP_BASE, dma_addr);
 
-	size = AIROHA_MAX_PACKET_SIZE * HW_DSCP_NUM;
-	if (!dmam_alloc_coherent(eth->dev, size, &dma_addr, GFP_KERNEL))
+	name = devm_kasprintf(eth->dev, GFP_KERNEL, "qdma%d-buf", id);
+	if (!name)
 		return -ENOMEM;
 
+	index = of_property_match_string(eth->dev->of_node,
+					 "memory-region-names", name);
+	if (index >= 0) {
+		struct reserved_mem *rmem;
+		struct device_node *np;
+
+		/* Consume reserved memory for hw forwarding buffers queue if
+		 * available in the DTS
+		 */
+		np = of_parse_phandle(eth->dev->of_node, "memory-region",
+				      index);
+		if (!np)
+			return -ENODEV;
+
+		rmem = of_reserved_mem_lookup(np);
+		of_node_put(np);
+		dma_addr = rmem->base;
+	} else {
+		size = AIROHA_MAX_PACKET_SIZE * HW_DSCP_NUM;
+		if (!dmam_alloc_coherent(eth->dev, size, &dma_addr,
+					 GFP_KERNEL))
+			return -ENOMEM;
+	}
+
 	airoha_qdma_wr(qdma, REG_FWD_BUF_BASE, dma_addr);
 
 	airoha_qdma_rmw(qdma, REG_HW_FWD_DSCP_CFG,