can: mcp251xfd: add HW timestamp infrastructure

This patch add the HW timestamping infrastructure. The mcp251xfd has a
free running timer of 32 bit width, running at max 40MHz, which wraps
around every 107 seconds. The current timestamp is latched into RX and
TEF objects automatically be the CAN controller.

This patch sets up a cyclecounter, timecounter and delayed worker
infrastructure (which runs every 45 seconds) to convert the timer into
a proper 64 bit based ns timestamp.

Link: https://lore.kernel.org/r/20210304160328.2752293-6-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/Makefile

@@ -6,5 +6,6 @@ mcp251xfd-objs :=
 mcp251xfd-objs += mcp251xfd-core.o
 mcp251xfd-objs += mcp251xfd-crc16.o
 mcp251xfd-objs += mcp251xfd-regmap.o
+mcp251xfd-objs += mcp251xfd-timestamp.o
 
 mcp251xfd-$(CONFIG_DEV_COREDUMP) += mcp251xfd-dump.o

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -2493,6 +2493,7 @@ static int mcp251xfd_open(struct net_device *ndev)
 	if (err)
 		goto out_transceiver_disable;
 
+	mcp251xfd_timestamp_init(priv);
 	can_rx_offload_enable(&priv->offload);
 
 	err = request_threaded_irq(spi->irq, NULL, mcp251xfd_irq,
@@ -2513,6 +2514,7 @@ static int mcp251xfd_open(struct net_device *ndev)
 	free_irq(spi->irq, priv);
  out_can_rx_offload_disable:
 	can_rx_offload_disable(&priv->offload);
+	mcp251xfd_timestamp_stop(priv);
  out_transceiver_disable:
 	mcp251xfd_transceiver_disable(priv);
  out_mcp251xfd_ring_free:
@@ -2534,6 +2536,7 @@ 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);

drivers/net/can/spi/mcp251xfd/mcp251xfd-timestamp.c

@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// mcp251xfd - Microchip MCP251xFD Family CAN controller driver
+//
+// Copyright (c) 2021 Pengutronix,
+//               Marc Kleine-Budde <kernel@pengutronix.de>
+//
+
+#include <linux/clocksource.h>
+#include <linux/workqueue.h>
+
+#include "mcp251xfd.h"
+
+static u64 mcp251xfd_timestamp_read(const struct cyclecounter *cc)
+{
+	struct mcp251xfd_priv *priv;
+	u32 timestamp = 0;
+	int err;
+
+	priv = container_of(cc, struct mcp251xfd_priv, cc);
+	err = mcp251xfd_get_timestamp(priv, &timestamp);
+	if (err)
+		netdev_err(priv->ndev,
+			   "Error %d while reading timestamp. HW timestamps may be inaccurate.",
+			   err);
+
+	return timestamp;
+}
+
+static void mcp251xfd_timestamp_work(struct work_struct *work)
+{
+	struct delayed_work *delayed_work = to_delayed_work(work);
+	struct mcp251xfd_priv *priv;
+
+	priv = container_of(delayed_work, struct mcp251xfd_priv, timestamp);
+	timecounter_read(&priv->tc);
+
+	schedule_delayed_work(&priv->timestamp,
+			      MCP251XFD_TIMESTAMP_WORK_DELAY_SEC * HZ);
+}
+
+void mcp251xfd_skb_set_timestamp(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->mask = CYCLECOUNTER_MASK(32);
+	cc->shift = 1;
+	cc->mult = clocksource_hz2mult(priv->can.clock.freq, cc->shift);
+
+	timecounter_init(&priv->tc, &priv->cc, ktime_get_real_ns());
+
+	INIT_DELAYED_WORK(&priv->timestamp, mcp251xfd_timestamp_work);
+	schedule_delayed_work(&priv->timestamp,
+			      MCP251XFD_TIMESTAMP_WORK_DELAY_SEC * HZ);
+}
+
+void mcp251xfd_timestamp_stop(struct mcp251xfd_priv *priv)
+{
+	cancel_delayed_work_sync(&priv->timestamp);
+}

drivers/net/can/spi/mcp251xfd/mcp251xfd.h

@@ -19,6 +19,8 @@
 #include <linux/regmap.h>
 #include <linux/regulator/consumer.h>
 #include <linux/spi/spi.h>
+#include <linux/timecounter.h>
+#include <linux/workqueue.h>
 
 /* MPC251x registers */
 
@@ -395,6 +397,9 @@
 #define MCP251XFD_SYSCLOCK_HZ_MAX 40000000
 #define MCP251XFD_SYSCLOCK_HZ_MIN 1000000
 #define MCP251XFD_SPICLOCK_HZ_MAX 20000000
+#define MCP251XFD_TIMESTAMP_WORK_DELAY_SEC 45
+static_assert(MCP251XFD_TIMESTAMP_WORK_DELAY_SEC <
+	      CYCLECOUNTER_MASK(32) / MCP251XFD_SYSCLOCK_HZ_MAX / 2);
 #define MCP251XFD_OSC_PLL_MULTIPLIER 10
 #define MCP251XFD_OSC_STAB_SLEEP_US (3 * USEC_PER_MSEC)
 #define MCP251XFD_OSC_STAB_TIMEOUT_US (10 * MCP251XFD_OSC_STAB_SLEEP_US)
@@ -596,6 +601,10 @@ struct mcp251xfd_priv {
 	struct mcp251xfd_ecc ecc;
 	struct mcp251xfd_regs_status regs_status;
 
+	struct cyclecounter cc;
+	struct timecounter tc;
+	struct delayed_work timestamp;
+
 	struct gpio_desc *rx_int;
 	struct clk *clk;
 	struct regulator *reg_vdd;
@@ -844,6 +853,10 @@ int mcp251xfd_regmap_init(struct mcp251xfd_priv *priv);
 u16 mcp251xfd_crc16_compute2(const void *cmd, size_t cmd_size,
 			     const void *data, size_t data_size);
 u16 mcp251xfd_crc16_compute(const void *data, size_t data_size);
+void mcp251xfd_skb_set_timestamp(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);
 
 #if IS_ENABLED(CONFIG_DEV_COREDUMP)
 void mcp251xfd_dump(const struct mcp251xfd_priv *priv);