[PATCH v2 0/5] can: mcp251xfd: workaround broken RX FIFO STA register read

[PATCH v2 0/5] can: mcp251xfd: workaround broken RX FIFO STA register read

[Marc Kleine-Budde]

Hello,

this is a to workaround for the broken RX FIFO STA register read
erratum found by Stefan Althöfer.

With the help of Thomas we found out that the chip has a time window
after receiving a CAN frame where the RX FIFO STA register content is
not read correctly.

From the driver's point of view, everything looks consistent at first,
but the head index of the chip is too large. This causes the driver to
rehandle old CAN frames that have already been processed.

The workaround uses the RX timestamp to distinguish between new and
old data. As soon as old data is found, processing is stopped.

The series applies against current net/main.

Happy testing,
Marc

Link: https://lore.kernel.org/all/FR0P281MB1966273C216630B120ABB6E197E89@FR0P281MB1966.DEUP281.PROD.OUTLOOK.COM

Changes since v1: https://lore.kernel.org/all/20230111222042.1139027-1-mkl@pengutronix.de
all:
  - add proper patch description
  - added Tested-by
2/5 can: mcp251xfd: clarify the meaning of timestamp:
  - revisited new naming of variables and functions
    now we use ts_raw instead of tbc
4/5 can: mcp251xfd: rx: prepare to workaround broken RX:
  - precalculate shift width needed for full u8 instead of calculating
    it every time
5/5 can: mcp251xfd: rx: workaround broken RX FIFO head:
  - remove dumping of old CAN frame in error case
  - add erratum comments

[PATCH v2 1/5] can: mcp251xfd: setup timestamping before mcp251xfd_ring_init()

[Marc Kleine-Budde]

This is a preparation patch.

An upcoming patch needs a valid timestamp in the callstack of
mcp251xfd_ring_init().

Move the initialization of the timestamp into mcp251xfd_chip_start()
before calling mcp251xfd_ring_init(). Move mcp251xfd_timestamp_stop()
accordingly.

Tested-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Tested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 .../net/can/spi/mcp251xfd/mcp251xfd-core.c    | 20 ++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
index 68df6d4641b5..4c0e3580efc1 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
@@ -736,6 +736,7 @@ static void mcp251xfd_chip_stop(struct mcp251xfd_priv *priv,
 {
 	priv->can.state = state;
 
+	mcp251xfd_timestamp_stop(priv);
 	mcp251xfd_chip_interrupts_disable(priv);
 	mcp251xfd_chip_rx_int_disable(priv);
 	mcp251xfd_chip_sleep(priv);
@@ -757,34 +758,38 @@ static int mcp251xfd_chip_start(struct mcp251xfd_priv *priv)
 	if (err)
 		goto out_chip_stop;
 
+	mcp251xfd_timestamp_init(priv);
+	
 	err = mcp251xfd_set_bittiming(priv);
 	if (err)
-		goto out_chip_stop;
+		goto out_timestamp_stop;
 
 	err = mcp251xfd_chip_rx_int_enable(priv);
 	if (err)
-		goto out_chip_stop;
+		goto out_timestamp_stop;
 
 	err = mcp251xfd_chip_ecc_init(priv);
 	if (err)
-		goto out_chip_stop;
+		goto out_timestamp_stop;
 
 	err = mcp251xfd_ring_init(priv);
 	if (err)
-		goto out_chip_stop;
+		goto out_timestamp_stop;
 
 	err = mcp251xfd_chip_fifo_init(priv);
 	if (err)
-		goto out_chip_stop;
+		goto out_timestamp_stop;
 
 	priv->can.state = CAN_STATE_ERROR_ACTIVE;
 
 	err = mcp251xfd_chip_set_normal_mode(priv);
 	if (err)
-		goto out_chip_stop;
+		goto out_timestamp_stop;
 
 	return 0;
 
+ out_timestamp_stop:
+	mcp251xfd_timestamp_stop(priv);
  out_chip_stop:
 	mcp251xfd_dump(priv);
 	mcp251xfd_chip_stop(priv, CAN_STATE_STOPPED);
@@ -1608,7 +1613,6 @@ static int mcp251xfd_open(struct net_device *ndev)
 	if (err)
 		goto out_transceiver_disable;
 
-	mcp251xfd_timestamp_init(priv);
 	clear_bit(MCP251XFD_FLAGS_DOWN, priv->flags);
 	can_rx_offload_enable(&priv->offload);
 
@@ -1631,7 +1635,6 @@ static int mcp251xfd_open(struct net_device *ndev)
  out_can_rx_offload_disable:
 	can_rx_offload_disable(&priv->offload);
 	set_bit(MCP251XFD_FLAGS_DOWN, priv->flags);
-	mcp251xfd_timestamp_stop(priv);
  out_transceiver_disable:
 	mcp251xfd_transceiver_disable(priv);
  out_mcp251xfd_ring_free:
@@ -1656,7 +1659,6 @@ static int mcp251xfd_stop(struct net_device *ndev)
 	mcp251xfd_chip_interrupts_disable(priv);
 	free_irq(ndev->irq, priv);
 	can_rx_offload_disable(&priv->offload);
-	mcp251xfd_timestamp_stop(priv);
 	mcp251xfd_chip_stop(priv, CAN_STATE_STOPPED);
 	mcp251xfd_transceiver_disable(priv);
 	mcp251xfd_ring_free(priv);
-- 
2.39.0

[PATCH v2 2/5] can: mcp251xfd: clarify the meaning of timestamp

[Marc Kleine-Budde]

The mcp251xfd chip is configured to provide a timestamp with each
received and transmitted CAN frame. The timestamp is derived from the
internal free-running timer, which can also be read from the TBC
register via SPI. The timer is 32 bits wide and is clocked by the
external oscillator (typically 20 or 40 MHz).

To avoid confusion, we call this timestamp "timestamp_raw" or "ts_raw"
for short.

Using the timecounter framework, the "ts_raw" is converted to 64 bit
nanoseconds since the epoch. This is what we call "timestamp".

This is a preparation for the next patches which use the "timestamp"
to work around a bug where so far only the "ts_raw" is used.

Tested-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Tested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 .../net/can/spi/mcp251xfd/mcp251xfd-core.c    | 28 +++++++++----------
 drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c  |  2 +-
 drivers/net/can/spi/mcp251xfd/mcp251xfd-tef.c |  2 +-
 .../can/spi/mcp251xfd/mcp251xfd-timestamp.c   | 22 ++++-----------
 drivers/net/can/spi/mcp251xfd/mcp251xfd.h     | 27 ++++++++++++++----
 5 files changed, 43 insertions(+), 38 deletions(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
index 4c0e3580efc1..5d7760803503 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
@@ -2,7 +2,7 @@
 //
 // mcp251xfd - Microchip MCP251xFD Family CAN controller driver
 //
-// Copyright (c) 2019, 2020, 2021 Pengutronix,
+// Copyright (c) 2019, 2020, 2021, 2023 Pengutronix,
 //               Marc Kleine-Budde <kernel@pengutronix.de>
 //
 // Based on:
@@ -866,18 +866,18 @@ static int mcp251xfd_get_berr_counter(const struct net_device *ndev,
 
 static struct sk_buff *
 mcp251xfd_alloc_can_err_skb(struct mcp251xfd_priv *priv,
-			    struct can_frame **cf, u32 *timestamp)
+			    struct can_frame **cf, u32 *ts_raw)
 {
 	struct sk_buff *skb;
 	int err;
 
-	err = mcp251xfd_get_timestamp(priv, timestamp);
+	err = mcp251xfd_get_timestamp_raw(priv, ts_raw);
 	if (err)
 		return NULL;
 
 	skb = alloc_can_err_skb(priv->ndev, cf);
 	if (skb)
-		mcp251xfd_skb_set_timestamp(priv, skb, *timestamp);
+		mcp251xfd_skb_set_timestamp_raw(priv, skb, *ts_raw);
 
 	return skb;
 }
@@ -888,7 +888,7 @@ static int mcp251xfd_handle_rxovif(struct mcp251xfd_priv *priv)
 	struct mcp251xfd_rx_ring *ring;
 	struct sk_buff *skb;
 	struct can_frame *cf;
-	u32 timestamp, rxovif;
+	u32 ts_raw, rxovif;
 	int err, i;
 
 	stats->rx_over_errors++;
@@ -923,14 +923,14 @@ static int mcp251xfd_handle_rxovif(struct mcp251xfd_priv *priv)
 			return err;
 	}
 
-	skb = mcp251xfd_alloc_can_err_skb(priv, &cf, &timestamp);
+	skb = mcp251xfd_alloc_can_err_skb(priv, &cf, &ts_raw);
 	if (!skb)
 		return 0;
 
 	cf->can_id |= CAN_ERR_CRTL;
 	cf->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
 
-	err = can_rx_offload_queue_timestamp(&priv->offload, skb, timestamp);
+	err = can_rx_offload_queue_timestamp(&priv->offload, skb, ts_raw);
 	if (err)
 		stats->rx_fifo_errors++;
 
@@ -947,12 +947,12 @@ static int mcp251xfd_handle_txatif(struct mcp251xfd_priv *priv)
 static int mcp251xfd_handle_ivmif(struct mcp251xfd_priv *priv)
 {
 	struct net_device_stats *stats = &priv->ndev->stats;
-	u32 bdiag1, timestamp;
+	u32 bdiag1, ts_raw;
 	struct sk_buff *skb;
 	struct can_frame *cf = NULL;
 	int err;
 
-	err = mcp251xfd_get_timestamp(priv, &timestamp);
+	err = mcp251xfd_get_timestamp_raw(priv, &ts_raw);
 	if (err)
 		return err;
 
@@ -1034,8 +1034,8 @@ static int mcp251xfd_handle_ivmif(struct mcp251xfd_priv *priv)
 	if (!cf)
 		return 0;
 
-	mcp251xfd_skb_set_timestamp(priv, skb, timestamp);
-	err = can_rx_offload_queue_timestamp(&priv->offload, skb, timestamp);
+	mcp251xfd_skb_set_timestamp_raw(priv, skb, ts_raw);
+	err = can_rx_offload_queue_timestamp(&priv->offload, skb, ts_raw);
 	if (err)
 		stats->rx_fifo_errors++;
 
@@ -1048,7 +1048,7 @@ static int mcp251xfd_handle_cerrif(struct mcp251xfd_priv *priv)
 	struct sk_buff *skb;
 	struct can_frame *cf = NULL;
 	enum can_state new_state, rx_state, tx_state;
-	u32 trec, timestamp;
+	u32 trec, ts_raw;
 	int err;
 
 	err = regmap_read(priv->map_reg, MCP251XFD_REG_TREC, &trec);
@@ -1078,7 +1078,7 @@ static int mcp251xfd_handle_cerrif(struct mcp251xfd_priv *priv)
 	/* The skb allocation might fail, but can_change_state()
 	 * handles cf == NULL.
 	 */
-	skb = mcp251xfd_alloc_can_err_skb(priv, &cf, &timestamp);
+	skb = mcp251xfd_alloc_can_err_skb(priv, &cf, &ts_raw);
 	can_change_state(priv->ndev, cf, tx_state, rx_state);
 
 	if (new_state == CAN_STATE_BUS_OFF) {
@@ -1109,7 +1109,7 @@ static int mcp251xfd_handle_cerrif(struct mcp251xfd_priv *priv)
 		cf->data[7] = bec.rxerr;
 	}
 
-	err = can_rx_offload_queue_timestamp(&priv->offload, skb, timestamp);
+	err = can_rx_offload_queue_timestamp(&priv->offload, skb, ts_raw);
 	if (err)
 		stats->rx_fifo_errors++;
 
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
index ced8d9c81f8c..6d66b97709b8 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
@@ -149,7 +149,7 @@ mcp251xfd_hw_rx_obj_to_skb(const struct mcp251xfd_priv *priv,
 	if (!(hw_rx_obj->flags & MCP251XFD_OBJ_FLAGS_RTR))
 		memcpy(cfd->data, hw_rx_obj->data, cfd->len);
 
-	mcp251xfd_skb_set_timestamp(priv, skb, hw_rx_obj->ts);
+	mcp251xfd_skb_set_timestamp_raw(priv, skb, hw_rx_obj->ts);
 }
 
 static int
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-tef.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-tef.c
index 237617b0c125..0c89e4f33976 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-tef.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-tef.c
@@ -109,7 +109,7 @@ mcp251xfd_handle_tefif_one(struct mcp251xfd_priv *priv,
 	tef_tail = mcp251xfd_get_tef_tail(priv);
 	skb = priv->can.echo_skb[tef_tail];
 	if (skb)
-		mcp251xfd_skb_set_timestamp(priv, skb, hw_tef_obj->ts);
+		mcp251xfd_skb_set_timestamp_raw(priv, skb, hw_tef_obj->ts);
 	stats->tx_bytes +=
 		can_rx_offload_get_echo_skb(&priv->offload,
 					    tef_tail, hw_tef_obj->ts,
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-timestamp.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-timestamp.c
index 712e09186987..1db99aabe85c 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-timestamp.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-timestamp.c
@@ -2,7 +2,7 @@
 //
 // mcp251xfd - Microchip MCP251xFD Family CAN controller driver
 //
-// Copyright (c) 2021 Pengutronix,
+// Copyright (c) 2021, 2023 Pengutronix,
 //               Marc Kleine-Budde <kernel@pengutronix.de>
 //
 
@@ -11,20 +11,20 @@
 
 #include "mcp251xfd.h"
 
-static u64 mcp251xfd_timestamp_read(const struct cyclecounter *cc)
+static u64 mcp251xfd_timestamp_raw_read(const struct cyclecounter *cc)
 {
 	const struct mcp251xfd_priv *priv;
-	u32 timestamp = 0;
+	u32 ts_raw = 0;
 	int err;
 
 	priv = container_of(cc, struct mcp251xfd_priv, cc);
-	err = mcp251xfd_get_timestamp(priv, &timestamp);
+	err = mcp251xfd_get_timestamp_raw(priv, &ts_raw);
 	if (err)
 		netdev_err(priv->ndev,
 			   "Error %d while reading timestamp. HW timestamps may be inaccurate.",
 			   err);
 
-	return timestamp;
+	return ts_raw;
 }
 
 static void mcp251xfd_timestamp_work(struct work_struct *work)
@@ -39,21 +39,11 @@ static void mcp251xfd_timestamp_work(struct work_struct *work)
 			      MCP251XFD_TIMESTAMP_WORK_DELAY_SEC * HZ);
 }
 
-void mcp251xfd_skb_set_timestamp(const struct mcp251xfd_priv *priv,
-				 struct sk_buff *skb, u32 timestamp)
-{
-	struct skb_shared_hwtstamps *hwtstamps = skb_hwtstamps(skb);
-	u64 ns;
-
-	ns = timecounter_cyc2time(&priv->tc, timestamp);
-	hwtstamps->hwtstamp = ns_to_ktime(ns);
-}
-
 void mcp251xfd_timestamp_init(struct mcp251xfd_priv *priv)
 {
 	struct cyclecounter *cc = &priv->cc;
 
-	cc->read = mcp251xfd_timestamp_read;
+	cc->read = mcp251xfd_timestamp_raw_read;
 	cc->mask = CYCLECOUNTER_MASK(32);
 	cc->shift = 1;
 	cc->mult = clocksource_hz2mult(priv->can.clock.freq, cc->shift);
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
index 2b0309fedfac..3c410c543dc8 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
@@ -2,7 +2,7 @@
  *
  * mcp251xfd - Microchip MCP251xFD Family CAN controller driver
  *
- * Copyright (c) 2019, 2020, 2021 Pengutronix,
+ * Copyright (c) 2019, 2020, 2021, 2023 Pengutronix,
  *               Marc Kleine-Budde <kernel@pengutronix.de>
  * Copyright (c) 2019 Martin Sperl <kernel@martin.sperl.org>
  */
@@ -786,10 +786,27 @@ mcp251xfd_spi_cmd_write(const struct mcp251xfd_priv *priv,
 	return data;
 }
 
-static inline int mcp251xfd_get_timestamp(const struct mcp251xfd_priv *priv,
-					  u32 *timestamp)
+static inline int mcp251xfd_get_timestamp_raw(const struct mcp251xfd_priv *priv,
+					      u32 *ts_raw)
 {
-	return regmap_read(priv->map_reg, MCP251XFD_REG_TBC, timestamp);
+	return regmap_read(priv->map_reg, MCP251XFD_REG_TBC, ts_raw);
+}
+
+static inline void mcp251xfd_skb_set_timestamp(struct sk_buff *skb, u64 ns)
+{
+	struct skb_shared_hwtstamps *hwtstamps = skb_hwtstamps(skb);
+
+	hwtstamps->hwtstamp = ns_to_ktime(ns);
+}
+
+static inline
+void mcp251xfd_skb_set_timestamp_raw(const struct mcp251xfd_priv *priv,
+				     struct sk_buff *skb, u32 ts_raw)
+{
+	u64 ns;
+
+	ns = timecounter_cyc2time(&priv->tc, ts_raw);
+	mcp251xfd_skb_set_timestamp(skb, ns);
 }
 
 static inline u16 mcp251xfd_get_tef_obj_addr(u8 n)
@@ -928,8 +945,6 @@ void mcp251xfd_ring_free(struct mcp251xfd_priv *priv);
 int mcp251xfd_ring_alloc(struct mcp251xfd_priv *priv);
 int mcp251xfd_handle_rxif(struct mcp251xfd_priv *priv);
 int mcp251xfd_handle_tefif(struct mcp251xfd_priv *priv);
-void mcp251xfd_skb_set_timestamp(const struct mcp251xfd_priv *priv,
-				 struct sk_buff *skb, u32 timestamp);
 void mcp251xfd_timestamp_init(struct mcp251xfd_priv *priv);
 void mcp251xfd_timestamp_stop(struct mcp251xfd_priv *priv);
 
-- 
2.39.0

[PATCH v2 3/5] can: mcp251xfd: mcp251xfd_handle_rxif_ring_uinc(): factor out in separate function

[Marc Kleine-Budde]

This is a preparation patch.

Sending the UINC messages followed by incrementing the tail pointer
will be called in more than one place in upcoming patches, so factor
this out into a separate function.

Also make mcp251xfd_handle_rxif_ring_uinc() safe to be called with a
"len" of 0.

Tested-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Tested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c | 48 +++++++++++++-------
 1 file changed, 32 insertions(+), 16 deletions(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
index 6d66b97709b8..2c2b057b7ac7 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
@@ -197,6 +197,37 @@ mcp251xfd_rx_obj_read(const struct mcp251xfd_priv *priv,
 	return err;
 }
 
+static int
+mcp251xfd_handle_rxif_ring_uinc(const struct mcp251xfd_priv *priv,
+				struct mcp251xfd_rx_ring *ring,
+				u8 len)
+{
+	int offset;
+	int err;
+
+	if (!len)
+		return 0;
+
+	/* Increment the RX FIFO tail pointer 'len' times in a
+	 * single SPI message.
+	 *
+	 * Note:
+	 * Calculate offset, so that the SPI transfer ends on
+	 * the last message of the uinc_xfer array, which has
+	 * "cs_change == 0", to properly deactivate the chip
+	 * select.
+	 */
+	offset = ARRAY_SIZE(ring->uinc_xfer) - len;
+	err = spi_sync_transfer(priv->spi,
+				ring->uinc_xfer + offset, len);
+	if (err)
+		return err;
+
+	ring->tail += len;
+
+	return 0;
+}
+
 static int
 mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 			   struct mcp251xfd_rx_ring *ring)
@@ -210,8 +241,6 @@ mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 		return err;
 
 	while ((len = mcp251xfd_get_rx_linear_len(ring))) {
-		int offset;
-
 		rx_tail = mcp251xfd_get_rx_tail(ring);
 
 		err = mcp251xfd_rx_obj_read(priv, ring, hw_rx_obj,
@@ -227,22 +256,9 @@ mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 				return err;
 		}
 
-		/* Increment the RX FIFO tail pointer 'len' times in a
-		 * single SPI message.
-		 *
-		 * Note:
-		 * Calculate offset, so that the SPI transfer ends on
-		 * the last message of the uinc_xfer array, which has
-		 * "cs_change == 0", to properly deactivate the chip
-		 * select.
-		 */
-		offset = ARRAY_SIZE(ring->uinc_xfer) - len;
-		err = spi_sync_transfer(priv->spi,
-					ring->uinc_xfer + offset, len);
+		err = mcp251xfd_handle_rxif_ring_uinc(priv, ring, len);
 		if (err)
 			return err;
-
-		ring->tail += len;
 	}
 
 	return 0;
-- 
2.39.0

[PATCH v2 4/5] can: mcp251xfd: rx: prepare to workaround broken RX FIFO head index erratum

[Marc Kleine-Budde]

This is a preparation patch to work around an erratum.

When handling the RX interrupt, the driver iterates over all pending
FIFOs (which are implemented as ring buffers in hardware) and reads
the FIFO header index from the RX FIFO STA register of the chip.

With the help of Thomas, we found out that the chip has a time window
after receiving a CAN frame where the content of the RX FIFO STA
register is not read correctly. In the bad case, we observed too large
head indices. In the original code, the driver always trusted the read
value, which caused old CAN frames that were already processed to be
reprocessed.

Instead of reading and trusting the head index, read the head index
and calculate the number of CAN frames that were supposedly received -
replace mcp251xfd_rx_ring_update() with mcp251xfd_get_rx_len().

The mcp251xfd_handle_rxif_ring() function reads the received CAN
frames from the chip, iterates over them and pushes them into the
network stack. Prepare that the iteration can be stopped if an old CAN
frame is detected. The actual code to detect old frames and abort will
be added in the next patch.

Link: https://lore.kernel.org/all/FR0P281MB1966273C216630B120ABB6E197E89@FR0P281MB1966.DEUP281.PROD.OUTLOOK.COM
Reported-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Tested-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Tested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 .../net/can/spi/mcp251xfd/mcp251xfd-ring.c    |  1 +
 drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c  | 77 +++++++++++++------
 drivers/net/can/spi/mcp251xfd/mcp251xfd.h     | 12 +--
 3 files changed, 57 insertions(+), 33 deletions(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
index bf3f0f150199..591ca0686df4 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
@@ -497,6 +497,7 @@ int mcp251xfd_ring_alloc(struct mcp251xfd_priv *priv)
 		}
 
 		rx_ring->obj_num = rx_obj_num;
+		rx_ring->obj_num_shift_to_u8 = BITS_PER_BYTE - ilog2(rx_obj_num);
 		rx_ring->obj_size = rx_obj_size;
 		priv->rx[i] = rx_ring;
 	}
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
index 2c2b057b7ac7..5c6cf2a3e2c2 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
@@ -2,7 +2,7 @@
 //
 // mcp251xfd - Microchip MCP251xFD Family CAN controller driver
 //
-// Copyright (c) 2019, 2020, 2021 Pengutronix,
+// Copyright (c) 2019, 2020, 2021, 2023 Pengutronix,
 //               Marc Kleine-Budde <kernel@pengutronix.de>
 //
 // Based on:
@@ -79,32 +79,59 @@ mcp251xfd_check_rx_tail(const struct mcp251xfd_priv *priv,
 	return 0;
 }
 
+static inline bool mcp251xfd_rx_fifo_sta_empty(u32 fifo_sta)
+{
+	return !(fifo_sta & MCP251XFD_REG_FIFOSTA_TFNRFNIF);
+}
+
+static inline bool mcp251xfd_rx_fifo_sta_full(u32 fifo_sta)
+{
+	return fifo_sta & MCP251XFD_REG_FIFOSTA_TFERFFIF;
+}
+
 static int
-mcp251xfd_rx_ring_update(const struct mcp251xfd_priv *priv,
-			 struct mcp251xfd_rx_ring *ring)
+mcp251xfd_get_rx_len(struct mcp251xfd_priv *priv,
+		     struct mcp251xfd_rx_ring *ring,
+		     u8 *len_p)
 {
-	u32 new_head;
-	u8 chip_rx_head;
-	bool fifo_empty;
+	u8 head, tail, shift, len;
+	u32 fifo_sta;
 	int err;
 
-	err = mcp251xfd_rx_head_get_from_chip(priv, ring, &chip_rx_head,
-					      &fifo_empty);
-	if (err || fifo_empty)
+	err = regmap_read(priv->map_reg, MCP251XFD_REG_FIFOSTA(ring->fifo_nr),
+			  &fifo_sta);
+	if (err)
 		return err;
 
-	/* chip_rx_head, is the next RX-Object filled by the HW.
-	 * The new RX head must be >= the old head.
-	 */
-	new_head = round_down(ring->head, ring->obj_num) + chip_rx_head;
-	if (new_head <= ring->head)
-		new_head += ring->obj_num;
+	if (mcp251xfd_rx_fifo_sta_empty(fifo_sta)) {
+		*len_p = 0;
+		return 0;
+	}
 
-	ring->head = new_head;
+	if (mcp251xfd_rx_fifo_sta_full(fifo_sta)) {
+		*len_p = ring->obj_num;
+		return 0;
+	}
+
+	head = FIELD_GET(MCP251XFD_REG_FIFOSTA_FIFOCI_MASK, fifo_sta);
+
+	err =  mcp251xfd_check_rx_tail(priv, ring);
+	if (err)
+		return err;
+	tail = mcp251xfd_get_rx_tail(ring);
 
-	return mcp251xfd_check_rx_tail(priv, ring);
+	/* First shift to full u8. The subtraction works on singed
+	 * values, that keeps the difference steady around the u8
+	 * overflow. The right shift acts on len, which is an u8.
+	 */
+	shift = ring->obj_num_shift_to_u8;
+	len = (head << shift) - (tail << shift);
+	*len_p = len >> shift;
+
+	return 0;
 }
 
+
 static void
 mcp251xfd_hw_rx_obj_to_skb(const struct mcp251xfd_priv *priv,
 			   const struct mcp251xfd_hw_rx_obj_canfd *hw_rx_obj,
@@ -208,6 +235,8 @@ mcp251xfd_handle_rxif_ring_uinc(const struct mcp251xfd_priv *priv,
 	if (!len)
 		return 0;
 
+	ring->head += len;
+
 	/* Increment the RX FIFO tail pointer 'len' times in a
 	 * single SPI message.
 	 *
@@ -233,22 +262,22 @@ mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 			   struct mcp251xfd_rx_ring *ring)
 {
 	struct mcp251xfd_hw_rx_obj_canfd *hw_rx_obj = ring->obj;
-	u8 rx_tail, len;
+	u8 rx_tail, len, l;
 	int err, i;
 
-	err = mcp251xfd_rx_ring_update(priv, ring);
+	err = mcp251xfd_get_rx_len(priv, ring, &len);
 	if (err)
 		return err;
 
-	while ((len = mcp251xfd_get_rx_linear_len(ring))) {
+	while ((l = mcp251xfd_get_rx_linear_len(ring, len))) {
 		rx_tail = mcp251xfd_get_rx_tail(ring);
 
 		err = mcp251xfd_rx_obj_read(priv, ring, hw_rx_obj,
-					    rx_tail, len);
+					    rx_tail, l);
 		if (err)
 			return err;
 
-		for (i = 0; i < len; i++) {
+		for (i = 0; i < l; i++) {
 			err = mcp251xfd_handle_rxif_one(priv, ring,
 							(void *)hw_rx_obj +
 							i * ring->obj_size);
@@ -256,9 +285,11 @@ mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 				return err;
 		}
 
-		err = mcp251xfd_handle_rxif_ring_uinc(priv, ring, len);
+		err = mcp251xfd_handle_rxif_ring_uinc(priv, ring, l);
 		if (err)
 			return err;
+
+		len -= l;
 	}
 
 	return 0;
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
index 3c410c543dc8..91cbc2451c8b 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
@@ -550,6 +550,7 @@ struct mcp251xfd_rx_ring {
 	u8 nr;
 	u8 fifo_nr;
 	u8 obj_num;
+	u8 obj_num_shift_to_u8;
 	u8 obj_size;
 
 	union mcp251xfd_write_reg_buf irq_enable_buf;
@@ -908,18 +909,9 @@ static inline u8 mcp251xfd_get_rx_tail(const struct mcp251xfd_rx_ring *ring)
 	return ring->tail & (ring->obj_num - 1);
 }
 
-static inline u8 mcp251xfd_get_rx_len(const struct mcp251xfd_rx_ring *ring)
-{
-	return ring->head - ring->tail;
-}
-
 static inline u8
-mcp251xfd_get_rx_linear_len(const struct mcp251xfd_rx_ring *ring)
+mcp251xfd_get_rx_linear_len(const struct mcp251xfd_rx_ring *ring, u8 len)
 {
-	u8 len;
-
-	len = mcp251xfd_get_rx_len(ring);
-
 	return min_t(u8, len, ring->obj_num - mcp251xfd_get_rx_tail(ring));
 }
 
-- 
2.39.0

[PATCH v2 5/5] can: mcp251xfd: rx: workaround broken RX FIFO head index erratum

[Marc Kleine-Budde]

With the help of Thomas, we found out that the chip has a time window
after receiving a CAN frame where the content of the RX FIFO STA
register (containing the RX FIFO head index) is not read correctly. In
the bad case, we observed too large head indices.

As the FIFO is implemented as a ring buffer, a too large head index
results in handling old CAN frames. To work around this issue, keep a
per FIFO timestamp [1] of the last valid received CAN frame and
compare against the timestamp of every received CAN frame. If an old
CAN frame is detected abort the iteration and mark the number of valid
CAN frames are processed in the chip by incrementing the FIFO's tail
index.

[1] As the raw timestamp overflows every 107 seconds (at the usual
    clock rate of 40 MHz) convert it to nanoseconds with the
    timecounter framework and use this to detect stale CAN frames.

Link: https://lore.kernel.org/all/FR0P281MB1966273C216630B120ABB6E197E89@FR0P281MB1966.DEUP281.PROD.OUTLOOK.COM
Reported-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Tested-by: Stefan Althöfer <Stefan.Althoefer@janztec.com>
Tested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 .../net/can/spi/mcp251xfd/mcp251xfd-ring.c    |  1 +
 drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c  | 28 +++++++++++++++++--
 drivers/net/can/spi/mcp251xfd/mcp251xfd.h     |  3 ++
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
index 591ca0686df4..f69d5fc8c9af 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c
@@ -196,6 +196,7 @@ mcp251xfd_ring_init_rx(struct mcp251xfd_priv *priv, u16 *base, u8 *fifo_nr)
 	int i, j;
 
 	mcp251xfd_for_each_rx_ring(priv, rx_ring, i) {
+		rx_ring->last_valid = timecounter_read(&priv->tc);
 		rx_ring->head = 0;
 		rx_ring->tail = 0;
 		rx_ring->base = *base;
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
index 5c6cf2a3e2c2..9ccca8d7b58d 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-rx.c
@@ -175,8 +175,6 @@ mcp251xfd_hw_rx_obj_to_skb(const struct mcp251xfd_priv *priv,
 
 	if (!(hw_rx_obj->flags & MCP251XFD_OBJ_FLAGS_RTR))
 		memcpy(cfd->data, hw_rx_obj->data, cfd->len);
-
-	mcp251xfd_skb_set_timestamp_raw(priv, skb, hw_rx_obj->ts);
 }
 
 static int
@@ -187,8 +185,23 @@ mcp251xfd_handle_rxif_one(struct mcp251xfd_priv *priv,
 	struct net_device_stats *stats = &priv->ndev->stats;
 	struct sk_buff *skb;
 	struct canfd_frame *cfd;
+	u64 timestamp;
 	int err;
 
+	/* Due to an erratum the RX FIFO head index might too big and
+	 * we're processing past the FIFO's head into old CAN frames.
+	 * Compared timestamp of current handled CAN frame against
+	 * last valid received one. Abort with -EBADMSG in case we
+	 * encounter an old CAN frame.
+	 */
+	timestamp = timecounter_cyc2time(&priv->tc, hw_rx_obj->ts);
+	if (timestamp <= ring->last_valid ) {
+		stats->rx_fifo_errors++;
+
+		return -EBADMSG;
+	}
+	ring->last_valid = timestamp;
+
 	if (hw_rx_obj->flags & MCP251XFD_OBJ_FLAGS_FDF)
 		skb = alloc_canfd_skb(priv->ndev, &cfd);
 	else
@@ -199,6 +212,7 @@ mcp251xfd_handle_rxif_one(struct mcp251xfd_priv *priv,
 		return 0;
 	}
 
+	mcp251xfd_skb_set_timestamp(skb, timestamp);
 	mcp251xfd_hw_rx_obj_to_skb(priv, hw_rx_obj, skb);
 	err = can_rx_offload_queue_timestamp(&priv->offload, skb, hw_rx_obj->ts);
 	if (err)
@@ -281,7 +295,15 @@ mcp251xfd_handle_rxif_ring(struct mcp251xfd_priv *priv,
 			err = mcp251xfd_handle_rxif_one(priv, ring,
 							(void *)hw_rx_obj +
 							i * ring->obj_size);
-			if (err)
+			/* -EBADMSG means we're affected by an
+			 * erratum, i.e. the timestamp in the RX
+			 * object is older that the last valid
+			 * received CAN frame. Don't process any
+			 * further.
+			 */
+			if (err == -EBADMSG)
+				return mcp251xfd_handle_rxif_ring_uinc(priv, ring, i);
+			else if (err)
 				return err;
 		}
 
diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
index 91cbc2451c8b..6008d38810e9 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
@@ -546,6 +546,9 @@ struct mcp251xfd_rx_ring {
 	unsigned int head;
 	unsigned int tail;
 
+	/* timestamp of the last valid received CAN frame */
+	u64 last_valid;
+
 	u16 base;
 	u8 nr;
 	u8 fifo_nr;
-- 
2.39.0