net: Add alignment support for net_buf data length alloc

The alignment value tells the amount of alignment of buffer length
when allocating net_buf data for sending. By default there is no
special alignment. This is needed for example with Nordic Wi-Fi
chip that uses SPI driver that expects 4 byte alignment for the
length of the data that is being sent.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>

Author: jukkar

subsys/net/ip/Kconfig

@@ -907,6 +907,18 @@ config NET_PKT_BUF_USER_DATA_SIZE
 	help
 	  User data size used in rx and tx network buffers.
 
+config NET_PKT_BUF_TX_DATA_ALLOC_ALIGN_LEN
+	int "Amount of alignment for TX net_buf allocations"
+	default 0
+	range 0 8
+	depends on NET_BUF_VARIABLE_DATA_SIZE
+	help
+	  This value tell amount of alignment of buffer length when allocating
+	  net_buf data for sending. By default there is no special alignment.
+	  This is needed for example with Nordic Wi-Fi chip that uses SPI driver
+	  that expects 4 byte alignment for the length of the data and the start
+	  of the data that is being sent.
+
 config NET_HEADERS_ALWAYS_CONTIGUOUS
 	bool
 	help

subsys/net/ip/net_pkt.c

@@ -142,8 +142,11 @@ NET_BUF_POOL_FIXED_DEFINE(tx_bufs, CONFIG_NET_BUF_TX_COUNT, CONFIG_NET_BUF_DATA_
 
 NET_BUF_POOL_VAR_DEFINE(rx_bufs, CONFIG_NET_BUF_RX_COUNT, CONFIG_NET_PKT_BUF_RX_DATA_POOL_SIZE,
 			CONFIG_NET_PKT_BUF_USER_DATA_SIZE, NULL);
-NET_BUF_POOL_VAR_DEFINE(tx_bufs, CONFIG_NET_BUF_TX_COUNT, CONFIG_NET_PKT_BUF_TX_DATA_POOL_SIZE,
-			CONFIG_NET_PKT_BUF_USER_DATA_SIZE, NULL);
+
+NET_BUF_POOL_VAR_ALIGN_DEFINE(tx_bufs, CONFIG_NET_BUF_TX_COUNT,
+			      CONFIG_NET_PKT_BUF_TX_DATA_POOL_SIZE,
+			      CONFIG_NET_PKT_BUF_USER_DATA_SIZE, NULL,
+			      CONFIG_NET_PKT_BUF_TX_DATA_ALLOC_ALIGN_LEN);
 
 #endif /* CONFIG_NET_BUF_FIXED_DATA_SIZE */
 

tests/drivers/wifi/nrf_wifi/testcase.yaml

@@ -40,3 +40,7 @@ tests:
   drivers.wifi.build.p2p:
     extra_configs:
       - CONFIG_NRF70_P2P_MODE=y
+  drivers.wifi.build.tx_align:
+    extra_configs:
+      - CONFIG_NET_PKT_BUF_TX_DATA_ALLOC_ALIGN_LEN=4
+      - CONFIG_NET_BUF_VARIABLE_DATA_SIZE=y