[PATCH net-next 1/3] net: stmmac: fpe: Enforce pmac_enabled in set_mm and keep it on at init

[muhammad.nazim.amirul.nazle.asmade at altera.com]

From: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade at altera.com>

The preemptive MAC in DWMAC is always enabled, meaning DWMAC is always
ready to receive preemptive mPackets. Initialize pmac_enabled to true
at init time and reject attempts to disable it via ethtool set_mm.

Also add a missing fpesel capability check in stmmac_set_mm() to return
-EOPNOTSUPP early on hardware without FPE support.

Signed-off-by: Rohan G Thomas <rohan.g.thomas at altera.com>
Signed-off-by: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade at altera.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c | 7 +++++++
 drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c     | 5 +++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
index 92585d27ab88..8ebdd249e5c8 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
@@ -1064,6 +1064,13 @@ static int stmmac_set_mm(struct net_device *ndev, struct ethtool_mm_cfg *cfg,
 	if (err)
 		return err;
 
+	if (!priv->dma_cap.fpesel)
+		return -EOPNOTSUPP;
+
+	/* DWMAC always have preemptible MAC enabled */
+	if (!cfg->pmac_enabled)
+		return -EINVAL;
+
 	stmmac_fpe_set_add_frag_size(priv, frag_size);
 	ethtool_mmsv_set_mm(&priv->fpe_cfg.mmsv, cfg);
 
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c
index c54c70224351..2f880c5e35b0 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c
@@ -176,6 +176,11 @@ void stmmac_fpe_init(struct stmmac_priv *priv)
 	if ((!priv->fpe_cfg.reg || !priv->hw->mac->fpe_map_preemption_class) &&
 	    priv->dma_cap.fpesel)
 		dev_info(priv->device, "FPE is not supported by driver.\n");
+
+	/* The preemptive MAC in DWMAC is always enabled, so initialize
+	 * pmac_enabled to true to reflect the hardware state.
+	 */
+	priv->fpe_cfg.mmsv.pmac_enabled = true;
 }
 
 int stmmac_fpe_get_add_frag_size(struct stmmac_priv *priv)
-- 
2.43.7