[PATCH net v5 0/4] MAC-PHY interrupt changed to level triggered interrupt

[PATCH net v5 0/4] MAC-PHY interrupt changed to level triggered interrupt

[Selvamani Rajagopal via B4 Relay]

According to OPEN Alliance 10BASE-T1x MAC-PHY Serial Interface
specification, MAC-PHY interrupt is "active low, level triggered".
The specification mentions about the conditions in which the IRQ
is asserted and deasserted.

Bug is inadvertently introduced by treating the IRQ in the OA TC6
framework driver and in dt-binding YAML file as edge triggered.

With the changes to use level triggered interrupt, use of threaded
irq is more efficient than the current method that has interrupt hander
working with work queue.

This change of interrupt handler mechanism exposed couple of race
conditions due to the fact that interrupts were not masked on protocol
error. And pointers were not initialized with null after skbs are freed.

Changes are done in two files
 - OA TC6 framework Ethernet driver
 - YAML file for the vendor that already uses OA TC6 framework.

Maintainer for this driver is already informed and aware of these
changes. Testing for these changes was done in onsemi's setup and
found to be working.

Changes in v5:
  - Removed the extraneous FCS that came with the frame before passing
    to the stack
  - Base commit was upadted on few patches to ensure that it is pointing
    to the correct commit ID.
  - Commit messages have been updated to be more descriptive and
    gives more detail now.
  - Couple of race conditions pointed out by AI review is fixed.

- Link to v4: https://lore.kernel.org/r/20260609-level-trigger-v4-0-6f389abdd192@onsemi.com

Changes in v4:

- IRQ handler is changed to interrupt handler + wake up thread
  to interrupt handler + threaded irq. Threaded irq mechanism
  is better suited for level triggered interrupt. Because it can
  keep the interrupt disabled until interrupting conditions are 
  handled by a handler thread.
- SPI data handling function is called again on EAGAIN error code
  as it indicates RX buffer overflow error, which requires draining
  the bad data chunks.
 
  - Changed wakeup thread to threaded IRQ 
  - RX buffer overflow is handled before threaded irq returns

- Link to v3: https://lore.kernel.org/r/20260601-level-trigger-v3-0-da73e7010532@onsemi.com

Signed-off-by: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>
---
Selvamani Rajagopal (4):
      net: ethernet: oa_tc6: Interrupt is active low, level triggered.
      net: ethernet: oa_tc6: mdiobus->parent initialized with NULL
      net: ethernet: oa_tc6: Remove FCS size in RX frame
      dt-bindings: net: updated interrupt type to be active low, level triggered

 .../devicetree/bindings/net/microchip,lan8650.yaml |   2 +-
 drivers/net/ethernet/oa_tc6.c                      | 140 +++++++++++++--------
 2 files changed, 89 insertions(+), 53 deletions(-)
---
base-commit: 22e2036479cb77df6281ebbd376ae6c330774790
change-id: 20260531-level-trigger-8cb1a83af034

Best regards,
--  
Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

[PATCH net v5 1/4] net: ethernet: oa_tc6: Interrupt is active low, level triggered.

[Selvamani Rajagopal via B4 Relay]

From: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

According OPEN Alliance 10BASET1x MAC-PHY Serial Interface
specification, interrupt is active low, level triggered.

Code used edge triggered interrupt which has the risk of losing an
interrupt on instances like when interrupt is disabled. Level
triggered interrupt won't be deasserted unless handler runs and
clear the interrupting conditions.

Interrupt handler mechanism is changed to threaded irq from
interrupt handler and kernel thread waiting on work queue.
Threaded irq mechanism is best suited for level triggered interrupt
as it disables the interrupt until handler is run in thread level,
while giving us an ability to have interrupt context handler to
signal the threaded irq handler.

Introduced a logic to disable the device interrupt on error. Error
could be due in data chunk's header and footer or SPI interface itself.
This will avoid having repeated interrupts, in case the driver couldn't
recover from the error condition with the available recovery mechanism.

Fixes: 2c6ce5354453 ("net: ethernet: oa_tc6: implement mac-phy interrupt")
Signed-off-by: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

---
changes in v5:
  - Updated the commit message to be more descriptive
  - Fixed the race condition between interrupt event and threaded
    irq to avoid interrupt storm and accessing skb after freed.
changes in v4:
  Interrupt handling mechanism changed to threaded irq
changes in v3:
 interrupt registered as level triggerred
---
 drivers/net/ethernet/oa_tc6.c | 126 +++++++++++++++++++++++++-----------------
 1 file changed, 76 insertions(+), 50 deletions(-)

diff --git a/drivers/net/ethernet/oa_tc6.c b/drivers/net/ethernet/oa_tc6.c
index 91a906a7918a..f3ac2875adfb 100644
--- a/drivers/net/ethernet/oa_tc6.c
+++ b/drivers/net/ethernet/oa_tc6.c
@@ -7,6 +7,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/iopoll.h>
+#include <linux/interrupt.h>
 #include <linux/mdio.h>
 #include <linux/phy.h>
 #include <linux/oa_tc6.h>
@@ -44,6 +45,8 @@
 #define INT_MASK0_LOSS_OF_FRAME_ERR_MASK	BIT(4)
 #define INT_MASK0_RX_BUFFER_OVERFLOW_ERR_MASK	BIT(3)
 #define INT_MASK0_TX_PROTOCOL_ERR_MASK		BIT(0)
+#define INT_MASK0_ALL_INTERRUPTS                (GENMASK(5, 0) | \
+						 GENMASK(12, 7))
 
 /* PHY Clause 22 registers base address and mask */
 #define OA_TC6_PHY_STD_REG_ADDR_BASE		0xFF00
@@ -121,14 +124,13 @@ struct oa_tc6 {
 	struct sk_buff *ongoing_tx_skb;
 	struct sk_buff *waiting_tx_skb;
 	struct sk_buff *rx_skb;
-	struct task_struct *spi_thread;
-	wait_queue_head_t spi_wq;
 	u16 tx_skb_offset;
 	u16 spi_data_tx_buf_offset;
 	u16 tx_credits;
 	u8 rx_chunks_available;
 	bool rx_buf_overflow;
 	bool int_flag;
+	bool disable_traffic;
 };
 
 enum oa_tc6_header_type {
@@ -669,6 +671,38 @@ static void oa_tc6_cleanup_ongoing_tx_skb(struct oa_tc6 *tc6)
 	}
 }
 
+static void oa_tc6_cleanup_waiting_tx_skb(struct oa_tc6 *tc6)
+{
+	if (tc6->waiting_tx_skb) {
+		tc6->netdev->stats.tx_dropped++;
+		kfree_skb(tc6->waiting_tx_skb);
+		tc6->waiting_tx_skb = NULL;
+	}
+}
+
+static void oa_tc6_free_pending_skbs(struct oa_tc6 *tc6)
+{
+	oa_tc6_cleanup_ongoing_tx_skb(tc6);
+	oa_tc6_cleanup_ongoing_rx_skb(tc6);
+	oa_tc6_cleanup_waiting_tx_skb(tc6);
+}
+
+/* If the failure is at SPI interface level, masking and clearing
+ * the interrupt of the device won't work. Since SPI interrupt is
+ * disabled, it should stop the repeated interrupts.
+ */
+static void oa_tc6_disable_traffic(struct oa_tc6 *tc6)
+{
+	u32 regval = INT_MASK0_ALL_INTERRUPTS;
+
+	tc6->disable_traffic = true;
+	oa_tc6_free_pending_skbs(tc6);
+	oa_tc6_write_register(tc6, OA_TC6_REG_INT_MASK0, regval);
+	oa_tc6_read_register(tc6, OA_TC6_REG_STATUS0, &regval);
+	oa_tc6_write_register(tc6, OA_TC6_REG_STATUS0, regval);
+	dev_err(&tc6->spi->dev, "Device interrupt disabled to avoid interrupt storm");
+}
+
 static int oa_tc6_process_extended_status(struct oa_tc6 *tc6)
 {
 	u32 value;
@@ -1105,29 +1139,29 @@ static int oa_tc6_try_spi_transfer(struct oa_tc6 *tc6)
 	return 0;
 }
 
-static int oa_tc6_spi_thread_handler(void *data)
+static irqreturn_t oa_tc6_macphy_threaded_irq(int irq, void *data)
 {
 	struct oa_tc6 *tc6 = data;
-	int ret;
-
-	while (likely(!kthread_should_stop())) {
-		/* This kthread will be waken up if there is a tx skb or mac-phy
-		 * interrupt to perform spi transfer with tx chunks.
-		 */
-		wait_event_interruptible(tc6->spi_wq, tc6->int_flag ||
-					 (tc6->waiting_tx_skb &&
-					 tc6->tx_credits) ||
-					 kthread_should_stop());
-
-		if (kthread_should_stop())
-			break;
+	int ret = 0;
 
-		ret = oa_tc6_try_spi_transfer(tc6);
-		if (ret)
-			return ret;
+	/* It is possible that interrupt woke the thread before it is
+	 * disabled. Until we come up with good recovery mechanism,
+	 * no need to attempt spi transfer, once it fails. Pending skbs
+	 * are already freed.
+	 */
+	if (!tc6->disable_traffic) {
+		while (tc6->int_flag ||
+		       (tc6->waiting_tx_skb && tc6->tx_credits)) {
+			ret = oa_tc6_try_spi_transfer(tc6);
+			if (ret) {
+				disable_irq_nosync(tc6->spi->irq);
+				oa_tc6_disable_traffic(tc6);
+				break;
+			}
+		}
 	}
 
-	return 0;
+	return IRQ_HANDLED;
 }
 
 static int oa_tc6_update_buffer_status_from_register(struct oa_tc6 *tc6)
@@ -1161,11 +1195,15 @@ static irqreturn_t oa_tc6_macphy_isr(int irq, void *data)
 	 *   the previous rx footer.
 	 * - extended status event not reported in the previous rx footer.
 	 */
-	tc6->int_flag = true;
-	/* Wake spi kthread to perform spi transfer */
-	wake_up_interruptible(&tc6->spi_wq);
-
-	return IRQ_HANDLED;
+	if (tc6->disable_traffic)
+		disable_irq_nosync(tc6->spi->irq);
+	else
+		tc6->int_flag = true;
+	/* Wake IRQ thread to perform spi transfer . In case
+	 * disable_traffic is set, threaded irq may run again
+	 * one more time.
+	 */
+	return IRQ_WAKE_THREAD;
 }
 
 /**
@@ -1202,7 +1240,7 @@ EXPORT_SYMBOL_GPL(oa_tc6_zero_align_receive_frame_enable);
  */
 netdev_tx_t oa_tc6_start_xmit(struct oa_tc6 *tc6, struct sk_buff *skb)
 {
-	if (tc6->waiting_tx_skb) {
+	if (tc6->disable_traffic || tc6->waiting_tx_skb) {
 		netif_stop_queue(tc6->netdev);
 		return NETDEV_TX_BUSY;
 	}
@@ -1217,8 +1255,8 @@ netdev_tx_t oa_tc6_start_xmit(struct oa_tc6 *tc6, struct sk_buff *skb)
 	tc6->waiting_tx_skb = skb;
 	spin_unlock_bh(&tc6->tx_skb_lock);
 
-	/* Wake spi kthread to perform spi transfer */
-	wake_up_interruptible(&tc6->spi_wq);
+	/* Wake the threaded IRQ to perform spi transfer. */
+	irq_wake_thread(tc6->spi->irq, tc6);
 
 	return NETDEV_TX_OK;
 }
@@ -1311,24 +1349,15 @@ struct oa_tc6 *oa_tc6_init(struct spi_device *spi, struct net_device *netdev)
 		goto phy_exit;
 	}
 
-	init_waitqueue_head(&tc6->spi_wq);
-
-	tc6->spi_thread = kthread_run(oa_tc6_spi_thread_handler, tc6,
-				      "oa-tc6-spi-thread");
-	if (IS_ERR(tc6->spi_thread)) {
-		dev_err(&tc6->spi->dev, "Failed to create SPI thread\n");
-		goto phy_exit;
-	}
-
-	sched_set_fifo(tc6->spi_thread);
-
-	ret = devm_request_irq(&tc6->spi->dev, tc6->spi->irq, oa_tc6_macphy_isr,
-			       IRQF_TRIGGER_FALLING, dev_name(&tc6->spi->dev),
-			       tc6);
+	ret = devm_request_threaded_irq(&tc6->spi->dev, tc6->spi->irq,
+					oa_tc6_macphy_isr,
+					oa_tc6_macphy_threaded_irq,
+					IRQF_TRIGGER_LOW | IRQF_ONESHOT,
+					dev_name(&tc6->spi->dev), tc6);
 	if (ret) {
 		dev_err(&tc6->spi->dev, "Failed to request macphy isr %d\n",
 			ret);
-		goto kthread_stop;
+		goto phy_exit;
 	}
 
 	/* oa_tc6_sw_reset_macphy() function resets and clears the MAC-PHY reset
@@ -1338,12 +1367,10 @@ struct oa_tc6 *oa_tc6_init(struct spi_device *spi, struct net_device *netdev)
 	 * 7.7 and 9.2.8.8 in the OPEN Alliance specification for more details.
 	 */
 	tc6->int_flag = true;
-	wake_up_interruptible(&tc6->spi_wq);
+	irq_wake_thread(tc6->spi->irq, tc6);
 
 	return tc6;
 
-kthread_stop:
-	kthread_stop(tc6->spi_thread);
 phy_exit:
 	oa_tc6_phy_exit(tc6);
 	return NULL;
@@ -1356,11 +1383,10 @@ EXPORT_SYMBOL_GPL(oa_tc6_init);
  */
 void oa_tc6_exit(struct oa_tc6 *tc6)
 {
+	tc6->disable_traffic = true;
+	disable_irq(tc6->spi->irq);
 	oa_tc6_phy_exit(tc6);
-	kthread_stop(tc6->spi_thread);
-	dev_kfree_skb_any(tc6->ongoing_tx_skb);
-	dev_kfree_skb_any(tc6->waiting_tx_skb);
-	dev_kfree_skb_any(tc6->rx_skb);
+	oa_tc6_free_pending_skbs(tc6);
 }
 EXPORT_SYMBOL_GPL(oa_tc6_exit);
 

-- 
2.43.0

[PATCH net v5 2/4] net: ethernet: oa_tc6: mdiobus->parent initialized with NULL

[Selvamani Rajagopal via B4 Relay]

From: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

As "dev" pointer in oa_tc6 structure is never initialized,
mbiobus->parent was initialized with NULL.  This change
fixes it by initializing it with device pointer of spi.

Fixes: 8f9bf857e43b ("net: ethernet: oa_tc6: implement internal PHY initialization")
Signed-off-by: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

---
changes in v5:
  Changed Fixes: commit ID to accurately reflect where issue originated
changes in v4:
   new patch
---
 drivers/net/ethernet/oa_tc6.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/oa_tc6.c b/drivers/net/ethernet/oa_tc6.c
index f3ac2875adfb..477ceefde2c5 100644
--- a/drivers/net/ethernet/oa_tc6.c
+++ b/drivers/net/ethernet/oa_tc6.c
@@ -110,7 +110,6 @@
 
 /* Internal structure for MAC-PHY drivers */
 struct oa_tc6 {
-	struct device *dev;
 	struct net_device *netdev;
 	struct phy_device *phydev;
 	struct mii_bus *mdiobus;
@@ -520,7 +519,7 @@ static int oa_tc6_mdiobus_register(struct oa_tc6 *tc6)
 	tc6->mdiobus->read_c45 = oa_tc6_mdiobus_read_c45;
 	tc6->mdiobus->write_c45 = oa_tc6_mdiobus_write_c45;
 	tc6->mdiobus->name = "oa-tc6-mdiobus";
-	tc6->mdiobus->parent = tc6->dev;
+	tc6->mdiobus->parent = &tc6->spi->dev;
 
 	snprintf(tc6->mdiobus->id, ARRAY_SIZE(tc6->mdiobus->id), "%s",
 		 dev_name(&tc6->spi->dev));

-- 
2.43.0

[PATCH net v5 3/4] net: ethernet: oa_tc6: Remove FCS size in RX frame

[Selvamani Rajagopal via B4 Relay]

From: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

OA TC6 MAC-PHY appends FCS to the incoming frame. It must be
removed from the frame before being passed to the stack.

With FCS in the frame, many applications, like ping or any
application that uses IP layer may work as they may
carry the packet size information in the protocol.

Application like ptp4l, particularly if it uses layer 2
for its communication, it will fail with "bad message" due to
the extra 4 bytes added by the presence of FCS.

Fixes: d70a0d8f2f2d ("net: ethernet: oa_tc6: implement receive path to receive rx ethernet frames")
Signed-off-by: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

---
changes in v5
  - Removed FCS present at the end of the MAC frame before being
    passed to the stack.
  - new patch
---
 drivers/net/ethernet/oa_tc6.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/net/ethernet/oa_tc6.c b/drivers/net/ethernet/oa_tc6.c
index 477ceefde2c5..0727d53345a3 100644
--- a/drivers/net/ethernet/oa_tc6.c
+++ b/drivers/net/ethernet/oa_tc6.c
@@ -785,6 +785,17 @@ static int oa_tc6_process_rx_chunk_footer(struct oa_tc6 *tc6, u32 footer)
 
 static void oa_tc6_submit_rx_skb(struct oa_tc6 *tc6)
 {
+	/* MAC-PHY delivers each frame with its Ethernet FCS attached.
+	 * Strip it before handing over to the stack, unless the user
+	 * has asked to keep it via NETIF_F_RXFCS. Keeping the FCS
+	 * in the frame is harmless for IP traffic, but is parsed as
+	 * a (malformed) suffix TLV by PTP, which makes ptp4l reject
+	 * every message with "bad message" error.
+	 */
+	if (!(tc6->netdev->features & NETIF_F_RXFCS) &&
+	    tc6->rx_skb->len > ETH_FCS_LEN)
+		skb_trim(tc6->rx_skb, tc6->rx_skb->len - ETH_FCS_LEN);
+
 	tc6->rx_skb->protocol = eth_type_trans(tc6->rx_skb, tc6->netdev);
 	tc6->netdev->stats.rx_packets++;
 	tc6->netdev->stats.rx_bytes += tc6->rx_skb->len;

-- 
2.43.0

[PATCH net v5 4/4] dt-bindings: net: updated interrupt type to be active low, level triggered

[Selvamani Rajagopal via B4 Relay]

From: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

According to OPEN Alliance 10BASE-T1x MACPHY Serial Interface (TC6)
specification, interrupt type is active low, level triggered interrupt.

Specification calls for when interrupt level will be asserted and what
condition it is de-asserted. By using edge triggered interrupt, there is a
potential chance to miss it, particularly if it is asserted when interrupt
is disabled.

Level triggered interrupt can't be missed as it gets de-asserted only on
interrupt handler taking actions on interrupting conditions.

Fixes: ac49b950bea9 ("dt-bindings: net: add Microchip's LAN865X 10BASE-T1S MACPHY")
Signed-off-by: Selvamani Rajagopal <Selvamani.Rajagopal@onsemi.com>

---
changes in v5
  Added better, descriptive commit message
changes in v4
  no change
changes in v3
  interrupts entry changed to level triggered from edge triggered
---
 Documentation/devicetree/bindings/net/microchip,lan8650.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/net/microchip,lan8650.yaml b/Documentation/devicetree/bindings/net/microchip,lan8650.yaml
index 61e11d4a07c4..766ff58147ae 100644
--- a/Documentation/devicetree/bindings/net/microchip,lan8650.yaml
+++ b/Documentation/devicetree/bindings/net/microchip,lan8650.yaml
@@ -67,7 +67,7 @@ examples:
         pinctrl-names = "default";
         pinctrl-0 = <&eth0_pins>;
         interrupt-parent = <&gpio>;
-        interrupts = <6 IRQ_TYPE_EDGE_FALLING>;
+        interrupts = <6 IRQ_TYPE_LEVEL_LOW>;
         local-mac-address = [04 05 06 01 02 03];
         spi-max-frequency = <15000000>;
       };

-- 
2.43.0