From fa249b49c9ca3a075e14f573bc1d51f98cddaaf6 Mon Sep 17 00:00:00 2001
From: Luca Toniolo <10792599+grandixximo@users.noreply.github.com>
Date: Wed, 3 Jun 2026 11:05:44 +0800
Subject: [PATCH] hm2_eth: don't abort board load when SIOCSARP is denied

---
 src/hal/drivers/mesa-hostmot2/hm2_eth.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/hal/drivers/mesa-hostmot2/hm2_eth.c b/src/hal/drivers/mesa-hostmot2/hm2_eth.c
index 2b426f8e419..48207908e5e 100644
--- a/src/hal/drivers/mesa-hostmot2/hm2_eth.c
+++ b/src/hal/drivers/mesa-hostmot2/hm2_eth.c
@@ -759,11 +759,17 @@ static int init_board(hm2_eth_t *board, const char *board_ip) {
         return ret;
     }
 
+    // Pinning the ARP entry needs CAP_NET_ADMIN; rootless without setcap
+    // fails with EPERM.  Best-effort, not fatal: fall back to dynamic ARP
+    // so the board still loads.  Clear ATF_PERM so the SIOCDARP teardown
+    // in close_board() does not try to remove an entry we never set.
     ret = ioctl_siocsarp(board);
     if(ret < 0) {
-        LL_PRINT("ERROR: ioctl SIOCSARP failed: %s\n", strerror(errno));
+        LL_PRINT("WARNING: ioctl SIOCSARP failed: %s; continuing with "
+                 "dynamic ARP.  Install file capabilities (sudo make "
+                 "setcap) or run setuid to pin the board's ARP entry and "
+                 "avoid occasional transmit latency.\n", strerror(errno));
         board->req.arp_flags &= ~ATF_PERM;
-        return -errno;
     }
 
     // install_iptables_board() is a no-op when iptables is unavailable