net: add generic selftest support

Port some parts of the stmmac selftest and reuse it as basic generic selftest
library. This patch was tested with following combinations:
- iMX6DL FEC -> AT8035
- iMX6DL FEC -> SJA1105Q switch -> KSZ8081
- iMX6DL FEC -> SJA1105Q switch -> KSZ9031
- AR9331 ag71xx -> AR9331 PHY
- AR9331 ag71xx -> AR9331 switch -> AR9331 PHY

Signed-off-by: Oleksij Rempel <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: olerem

include/net/selftests.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NET_SELFTESTS
+#define _NET_SELFTESTS
+
+#include <linux/ethtool.h>
+
+void net_selftest(struct net_device *ndev, struct ethtool_test *etest,
+		  u64 *buf);
+int net_selftest_get_count(void);
+void net_selftest_get_strings(u8 *data);
+
+#endif /* _NET_SELFTESTS */

net/Kconfig

@@ -429,6 +429,10 @@ config GRO_CELLS
 config SOCK_VALIDATE_XMIT
 	bool
 
+config NET_SELFTESTS
+	def_tristate PHYLIB
+	depends on PHYLIB
+
 config NET_SOCK_MSG
 	bool
 	default n

net/core/Makefile

@@ -33,6 +33,7 @@ obj-$(CONFIG_NET_DEVLINK) += devlink.o
 obj-$(CONFIG_GRO_CELLS) += gro_cells.o
 obj-$(CONFIG_FAILOVER) += failover.o
 ifeq ($(CONFIG_INET),y)
+obj-$(CONFIG_NET_SELFTESTS) += selftests.o
 obj-$(CONFIG_NET_SOCK_MSG) += skmsg.o
 obj-$(CONFIG_BPF_SYSCALL) += sock_map.o
 endif