[PATCH net-next v5 2/5] net: cadence: macb: implement EEE TX LPI support
From: Nicolai Buchwitz
Date: Fri Feb 27 2026 - 10:13:42 EST
The GEM MAC has hardware LPI registers (NCR bit 19: TXLPIEN) but no
built-in idle timer, so asserting TXLPIEN blocks all TX immediately
with no automatic wake. A software idle timer is required, as noted
in Microchip documentation (section 40.6.19): "It is best to use
firmware to control LPI."
Implement phylink managed EEE using the mac_enable_tx_lpi and
mac_disable_tx_lpi callbacks:
- macb_tx_lpi_set(): atomically sets or clears TXLPIEN under the
existing bp->lock spinlock; returns bool indicating whether the
register actually changed, avoiding redundant writes.
- macb_tx_lpi_work_fn(): delayed_work handler that enters LPI if all
TX queues are idle and EEE is still active.
- macb_tx_lpi_schedule(): arms the work timer using the LPI timer
value provided by phylink (default 250 ms). Called from
macb_tx_complete() after each TX drain so the idle countdown
restarts whenever the ring goes quiet.
- macb_tx_lpi_wake(): called from macb_start_xmit() before TSTART.
Clears TXLPIEN and applies a 50 us udelay for PHY wake (IEEE
802.3az Tw_sys_tx is 16.5 us for 1000BASE-T / 30 us for
100BASE-TX; GEM has no hardware enforcement). Only delays when
TXLPIEN was actually set, avoiding overhead on the common path.
The delay is placed after tx_head is advanced so the work_fn's
queue-idle check sees a non-empty ring and cannot race back into
LPI before the frame is transmitted.
- mac_enable_tx_lpi: stores the timer and sets eee_active, then
defers the first LPI entry by 1 second per IEEE 802.3az section
22.7a.
- mac_disable_tx_lpi: clears eee_active, cancels the work, and
deasserts TXLPIEN.
Populate phylink_config lpi_interfaces (MII, GMII, RGMII variants)
and lpi_capabilities (MAC_100FD | MAC_1000FD) so phylink can
negotiate EEE with the PHY and call the callbacks appropriately.
Set lpi_timer_default to 250000 us and eee_enabled_default to true.
Reviewed-by: Théo Lebrun <theo.lebrun@xxxxxxxxxxx>
Signed-off-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>
---
drivers/net/ethernet/cadence/macb.h | 8 ++
drivers/net/ethernet/cadence/macb_main.c | 112 +++++++++++++++++++++++
2 files changed, 120 insertions(+)
diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
index 19aa98d01c8c..c69828b27dae 100644
--- a/drivers/net/ethernet/cadence/macb.h
+++ b/drivers/net/ethernet/cadence/macb.h
@@ -309,6 +309,8 @@
#define MACB_IRXFCS_SIZE 1
/* GEM specific NCR bitfields. */
+#define GEM_TXLPIEN_OFFSET 19
+#define GEM_TXLPIEN_SIZE 1
#define GEM_ENABLE_HS_MAC_OFFSET 31
#define GEM_ENABLE_HS_MAC_SIZE 1
@@ -783,6 +785,7 @@
#define MACB_CAPS_DMA_PTP BIT(22)
#define MACB_CAPS_RSC BIT(23)
#define MACB_CAPS_NO_LSO BIT(24)
+#define MACB_CAPS_EEE BIT(25)
/* LSO settings */
#define MACB_LSO_UFO_ENABLE 0x01
@@ -1369,6 +1372,11 @@ struct macb {
struct work_struct hresp_err_bh_work;
+ /* EEE / LPI state */
+ bool eee_active;
+ struct delayed_work tx_lpi_work;
+ u32 tx_lpi_timer;
+
int rx_bd_rd_prefetch;
int tx_bd_rd_prefetch;
diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 02eab26fd98b..c23485f049d3 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -10,6 +10,7 @@
#include <linux/clk-provider.h>
#include <linux/clk.h>
#include <linux/crc32.h>
+#include <linux/delay.h>
#include <linux/dma-mapping.h>
#include <linux/etherdevice.h>
#include <linux/firmware/xlnx-zynqmp.h>
@@ -621,6 +622,94 @@ static const struct phylink_pcs_ops macb_phylink_pcs_ops = {
.pcs_config = macb_pcs_config,
};
+static bool macb_tx_lpi_set(struct macb *bp, bool enable)
+{
+ unsigned long flags;
+ u32 old, ncr;
+
+ spin_lock_irqsave(&bp->lock, flags);
+ ncr = macb_readl(bp, NCR);
+ old = ncr;
+ if (enable)
+ ncr |= GEM_BIT(TXLPIEN);
+ else
+ ncr &= ~GEM_BIT(TXLPIEN);
+ if (old != ncr)
+ macb_writel(bp, NCR, ncr);
+ spin_unlock_irqrestore(&bp->lock, flags);
+
+ return old != ncr;
+}
+
+static bool macb_tx_all_queues_idle(struct macb *bp)
+{
+ unsigned int q;
+
+ for (q = 0; q < bp->num_queues; q++) {
+ struct macb_queue *queue = &bp->queues[q];
+
+ if (queue->tx_head != queue->tx_tail)
+ return false;
+ }
+ return true;
+}
+
+static void macb_tx_lpi_work_fn(struct work_struct *work)
+{
+ struct macb *bp = container_of(work, struct macb, tx_lpi_work.work);
+
+ if (bp->eee_active && macb_tx_all_queues_idle(bp))
+ macb_tx_lpi_set(bp, true);
+}
+
+static void macb_tx_lpi_schedule(struct macb *bp)
+{
+ if (bp->eee_active)
+ mod_delayed_work(system_wq, &bp->tx_lpi_work,
+ usecs_to_jiffies(bp->tx_lpi_timer));
+}
+
+/* Wake from LPI before transmitting. The MAC must deassert TXLPIEN
+ * and wait for the PHY to exit LPI before any frame can be sent.
+ * IEEE 802.3az Tw_sys is ~17us for 1000BASE-T, ~30us for 100BASE-TX;
+ * we use a conservative 50us.
+ */
+static void macb_tx_lpi_wake(struct macb *bp)
+{
+ if (!macb_tx_lpi_set(bp, false))
+ return;
+
+ cancel_delayed_work(&bp->tx_lpi_work);
+ udelay(50);
+}
+
+static void macb_mac_disable_tx_lpi(struct phylink_config *config)
+{
+ struct net_device *ndev = to_net_dev(config->dev);
+ struct macb *bp = netdev_priv(ndev);
+
+ bp->eee_active = false;
+ cancel_delayed_work_sync(&bp->tx_lpi_work);
+ macb_tx_lpi_set(bp, false);
+}
+
+static int macb_mac_enable_tx_lpi(struct phylink_config *config, u32 timer,
+ bool tx_clk_stop)
+{
+ struct net_device *ndev = to_net_dev(config->dev);
+ struct macb *bp = netdev_priv(ndev);
+
+ bp->tx_lpi_timer = timer;
+ bp->eee_active = true;
+
+ /* Defer initial LPI entry by 1 second after link-up per
+ * IEEE 802.3az section 22.7a.
+ */
+ mod_delayed_work(system_wq, &bp->tx_lpi_work, msecs_to_jiffies(1000));
+
+ return 0;
+}
+
static void macb_mac_config(struct phylink_config *config, unsigned int mode,
const struct phylink_link_state *state)
{
@@ -769,6 +858,8 @@ static const struct phylink_mac_ops macb_phylink_ops = {
.mac_config = macb_mac_config,
.mac_link_down = macb_mac_link_down,
.mac_link_up = macb_mac_link_up,
+ .mac_disable_tx_lpi = macb_mac_disable_tx_lpi,
+ .mac_enable_tx_lpi = macb_mac_enable_tx_lpi,
};
static bool macb_phy_handle_exists(struct device_node *dn)
@@ -864,6 +955,18 @@ static int macb_mii_probe(struct net_device *dev)
}
}
+ /* Configure EEE LPI if supported */
+ if (bp->caps & MACB_CAPS_EEE) {
+ __set_bit(PHY_INTERFACE_MODE_MII,
+ bp->phylink_config.lpi_interfaces);
+ __set_bit(PHY_INTERFACE_MODE_GMII,
+ bp->phylink_config.lpi_interfaces);
+ phy_interface_set_rgmii(bp->phylink_config.lpi_interfaces);
+ bp->phylink_config.lpi_capabilities = MAC_100FD | MAC_1000FD;
+ bp->phylink_config.lpi_timer_default = 250000;
+ bp->phylink_config.eee_enabled_default = true;
+ }
+
bp->phylink = phylink_create(&bp->phylink_config, bp->pdev->dev.fwnode,
bp->phy_interface, &macb_phylink_ops);
if (IS_ERR(bp->phylink)) {
@@ -1260,6 +1363,9 @@ static int macb_tx_complete(struct macb_queue *queue, int budget)
netif_wake_subqueue(bp->dev, queue_index);
spin_unlock_irqrestore(&queue->tx_ptr_lock, flags);
+ if (packets)
+ macb_tx_lpi_schedule(bp);
+
return packets;
}
@@ -2365,6 +2471,8 @@ static netdev_tx_t macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
netdev_tx_sent_queue(netdev_get_tx_queue(bp->dev, queue_index),
skb->len);
+ macb_tx_lpi_wake(bp);
+
spin_lock(&bp->lock);
macb_writel(bp, NCR, macb_readl(bp, NCR) | MACB_BIT(TSTART));
spin_unlock(&bp->lock);
@@ -3026,6 +3134,8 @@ static int macb_close(struct net_device *dev)
netdev_tx_reset_queue(netdev_get_tx_queue(dev, q));
}
+ cancel_delayed_work_sync(&bp->tx_lpi_work);
+
phylink_stop(bp->phylink);
phylink_disconnect_phy(bp->phylink);
@@ -5633,6 +5743,7 @@ static int macb_probe(struct platform_device *pdev)
}
INIT_WORK(&bp->hresp_err_bh_work, macb_hresp_error_task);
+ INIT_DELAYED_WORK(&bp->tx_lpi_work, macb_tx_lpi_work_fn);
netdev_info(dev, "Cadence %s rev 0x%08x at 0x%08lx irq %d (%pM)\n",
macb_is_gem(bp) ? "GEM" : "MACB", macb_readl(bp, MID),
@@ -5676,6 +5787,7 @@ static void macb_remove(struct platform_device *pdev)
mdiobus_free(bp->mii_bus);
device_set_wakeup_enable(&bp->pdev->dev, 0);
+ cancel_delayed_work_sync(&bp->tx_lpi_work);
cancel_work_sync(&bp->hresp_err_bh_work);
pm_runtime_disable(&pdev->dev);
pm_runtime_dont_use_autosuspend(&pdev->dev);
--
2.51.0