[PATCH net] net: enetc: fix potential divide-by-zero when num_vsi is zero

[wei.fang@oss.nxp.com]

From: Wei Fang <wei.fang@nxp.com>

For i.MX94 series, all the standalone ENETCs do not support SR-IOV, so
pf->caps.num_vsi is zero. This leads to a divide-by-zero in
enetc4_default_rings_allocation() when distributing rings among PF and
VFs.

Division by zero is undefined behavior in C. On ARM64, the UDIV/SDIV
instructions silently return zero rather than raising an exception, so
the issue does not cause a visible crash. However, relying on this
behavior is incorrect and poses a cross-platform compatibility risk.

Add an explicit check for num_vsi == 0 and return early after the PF's
rings have been configured.

Fixes: 2d673b0e2f8d ("net: enetc: add standalone ENETC support for i.MX94")
Signed-off-by: Wei Fang <wei.fang@nxp.com>
---
 drivers/net/ethernet/freescale/enetc/enetc4_pf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc4_pf.c b/drivers/net/ethernet/freescale/enetc/enetc4_pf.c
index 4e771f852358..437a15bbb47b 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc4_pf.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc4_pf.c
@@ -322,6 +322,9 @@ static void enetc4_default_rings_allocation(struct enetc_pf *pf)
 	val = enetc4_psicfgr0_val_construct(false, num_tx_bdr, num_rx_bdr);
 	enetc_port_wr(hw, ENETC4_PSICFGR0(0), val);
 
+	if (!pf->caps.num_vsi)
+		return;
+
 	num_rx_bdr = pf->caps.num_rx_bdr - num_rx_bdr;
 	rx_rem = num_rx_bdr % pf->caps.num_vsi;
 	num_rx_bdr = num_rx_bdr / pf->caps.num_vsi;
-- 
2.34.1