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From: =?UTF-8?q?Martin=20Hundeb=C3=B8ll?= <martin@geanix.com>
To: Chandrasekar Ramakrishnan <rcsekar@samsung.com>,
	Marc Kleine-Budde <mkl@pengutronix.de>,
	Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Paolo Abeni <pabeni@redhat.com>
Cc: Markus Schneider-Pargmann <msp@baylibre.com>,
	=?UTF-8?q?Martin=20Hundeb=C3=B8ll?= <martin@geanix.com>,
	linux-can@vger.kernel.org,
	netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2] can: m_can: don't enable transceiver when probing
Date: Wed,  1 May 2024 14:42:03 +0200
Message-ID: <20240501124204.3545056-1-martin@geanix.com>
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The m_can driver sets and clears the CCCR.INIT bit during probe (both
when testing the NON-ISO bit, and when configuring the chip). After
clearing the CCCR.INIT bit, the transceiver enters normal mode, where it
affects the CAN bus (i.e. it ACKs frames). This can cause troubles when
the m_can node is only used for monitoring the bus, as one cannot setup
listen-only mode before the device is probed.

Rework the probe flow, so that the CCCR.INIT bit is only cleared when
upping the device. First, the tcan4x5x driver is changed to stay in
standby mode during/after probe. This in turn requires changes when
setting bits in the CCCR register, as its CSR and CSA bits are always
high in standby mode.

Signed-off-by: Martin Hundebøll <martin@geanix.com>
---

Changes since v1:
 * Implement Markus review comments:
   - Rename m_can_cccr_wait_bits() to m_can_cccr_update_bits()
   - Explicitly set CCCR_INIT bit in m_can_dev_setup()
   - Revert to 5 timeouts/tries to 10
   - Use m_can_config_{en|dis}able() in m_can_niso_supported()
   - Revert move of call to m_can_enable_all_interrupts()
   - Return -EBUSY on failure to enter normal mode
   - Use tcan4x5x_clear_interrupts() in tcan4x5x_can_probe()

 drivers/net/can/m_can/m_can.c         | 131 +++++++++++++++-----------
 drivers/net/can/m_can/tcan4x5x-core.c |  13 ++-
 2 files changed, 85 insertions(+), 59 deletions(-)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index 14b231c4d7ec..7974aaa5d8cc 100644
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -379,38 +379,60 @@ m_can_txe_fifo_read(struct m_can_classdev *cdev, u32 fgi, u32 offset, u32 *val)
 	return cdev->ops->read_fifo(cdev, addr_offset, val, 1);
 }
 
-static void m_can_config_endisable(struct m_can_classdev *cdev, bool enable)
+static bool m_can_cccr_update_bits(struct m_can_classdev *cdev, u32 mask, u32 val)
 {
-	u32 cccr = m_can_read(cdev, M_CAN_CCCR);
-	u32 timeout = 10;
-	u32 val = 0;
-
-	/* Clear the Clock stop request if it was set */
-	if (cccr & CCCR_CSR)
-		cccr &= ~CCCR_CSR;
-
-	if (enable) {
-		/* enable m_can configuration */
-		m_can_write(cdev, M_CAN_CCCR, cccr | CCCR_INIT);
-		udelay(5);
-		/* CCCR.CCE can only be set/reset while CCCR.INIT = '1' */
-		m_can_write(cdev, M_CAN_CCCR, cccr | CCCR_INIT | CCCR_CCE);
-	} else {
-		m_can_write(cdev, M_CAN_CCCR, cccr & ~(CCCR_INIT | CCCR_CCE));
-	}
+	u32 val_before = m_can_read(cdev, M_CAN_CCCR);
+	u32 val_after = (val_before & ~mask) | val;
+	size_t tries = 10;
+
+	if (!(mask & CCCR_INIT) && !(val_before & CCCR_INIT))
+		dev_warn(cdev->dev,
+			 "trying to configure device when in normal mode. Expect failures\n");
+
+	/* The chip should be in standby mode when changing the CCCR register,
+	 * and some chips set the CSR and CSA bits when in standby. Furthermore,
+	 * the CSR and CSA bits should be written as zeros, even when they read
+	 * ones.
+	 */
+	val_after &= ~(CCCR_CSR | CCCR_CSA);
+
+	while (tries--) {
+		u32 val_read;
+
+		/* Write the desired value in each try, as setting some bits in
+		 * the CCCR register require other bits to be set first. E.g.
+		 * setting the NISO bit requires setting the CCE bit first.
+		 */
+		m_can_write(cdev, M_CAN_CCCR, val_after);
+
+		val_read = m_can_read(cdev, M_CAN_CCCR) & ~(CCCR_CSR | CCCR_CSA);
 
-	/* there's a delay for module initialization */
-	if (enable)
-		val = CCCR_INIT | CCCR_CCE;
-
-	while ((m_can_read(cdev, M_CAN_CCCR) & (CCCR_INIT | CCCR_CCE)) != val) {
-		if (timeout == 0) {
-			netdev_warn(cdev->net, "Failed to init module\n");
-			return;
-		}
-		timeout--;
-		udelay(1);
+		if (val_read == val_after)
+			return true;
+
+		usleep_range(1, 5);
 	}
+
+	return false;
+}
+
+static void m_can_config_enable(struct m_can_classdev *cdev)
+{
+	/* CCCR_INIT must be set in order to set CCCR_CCE, but access to
+	 * configuration registers should only be enabled when in standby mode,
+	 * where CCCR_INIT is always set.
+	 */
+	if (!m_can_cccr_update_bits(cdev, CCCR_CCE, CCCR_CCE))
+		netdev_err(cdev->net, "failed to enable configuration mode\n");
+}
+
+static void m_can_config_disable(struct m_can_classdev *cdev)
+{
+	/* Only clear CCCR_CCE, since CCCR_INIT cannot be cleared while in
+	 * standby mode
+	 */
+	if (!m_can_cccr_update_bits(cdev, CCCR_CCE, 0))
+		netdev_err(cdev->net, "failed to disable configuration registers\n");
 }
 
 static void m_can_interrupt_enable(struct m_can_classdev *cdev, u32 interrupts)
@@ -1403,7 +1425,7 @@ static int m_can_chip_config(struct net_device *dev)
 	interrupts &= ~(IR_ARA | IR_ELO | IR_DRX | IR_TEFF | IR_TFE | IR_TCF |
 			IR_HPM | IR_RF1F | IR_RF1W | IR_RF1N | IR_RF0F);
 
-	m_can_config_endisable(cdev, true);
+	m_can_config_enable(cdev);
 
 	/* RX Buffer/FIFO Element Size 64 bytes data field */
 	m_can_write(cdev, M_CAN_RXESC,
@@ -1521,7 +1543,7 @@ static int m_can_chip_config(struct net_device *dev)
 		    FIELD_PREP(TSCC_TCP_MASK, 0xf) |
 		    FIELD_PREP(TSCC_TSS_MASK, TSCC_TSS_INTERNAL));
 
-	m_can_config_endisable(cdev, false);
+	m_can_config_disable(cdev);
 
 	if (cdev->ops->init)
 		cdev->ops->init(cdev);
@@ -1550,6 +1572,11 @@ static int m_can_start(struct net_device *dev)
 		cdev->tx_fifo_putidx = FIELD_GET(TXFQS_TFQPI_MASK,
 						 m_can_read(cdev, M_CAN_TXFQS));
 
+	if (!m_can_cccr_update_bits(cdev, CCCR_INIT, 0)) {
+		netdev_err(dev, "failed to enter normal mode\n");
+		return -EBUSY;
+	}
+
 	return 0;
 }
 
@@ -1603,33 +1630,20 @@ static int m_can_check_core_release(struct m_can_classdev *cdev)
  */
 static bool m_can_niso_supported(struct m_can_classdev *cdev)
 {
-	u32 cccr_reg, cccr_poll = 0;
-	int niso_timeout = -ETIMEDOUT;
-	int i;
+	bool niso_supported;
 
-	m_can_config_endisable(cdev, true);
-	cccr_reg = m_can_read(cdev, M_CAN_CCCR);
-	cccr_reg |= CCCR_NISO;
-	m_can_write(cdev, M_CAN_CCCR, cccr_reg);
+	m_can_config_enable(cdev);
 
-	for (i = 0; i <= 10; i++) {
-		cccr_poll = m_can_read(cdev, M_CAN_CCCR);
-		if (cccr_poll == cccr_reg) {
-			niso_timeout = 0;
-			break;
-		}
+	/* First try to set the NISO bit. */
+	niso_supported = m_can_cccr_update_bits(cdev, CCCR_NISO, CCCR_NISO);
 
-		usleep_range(1, 5);
-	}
+	/* Then clear the it again. */
+	if (!m_can_cccr_update_bits(cdev, CCCR_NISO, 0))
+		dev_err(cdev->dev, "failed to revert the NON-ISO bit in CCCR\n");
 
-	/* Clear NISO */
-	cccr_reg &= ~(CCCR_NISO);
-	m_can_write(cdev, M_CAN_CCCR, cccr_reg);
+	m_can_config_disable(cdev);
 
-	m_can_config_endisable(cdev, false);
-
-	/* return false if time out (-ETIMEDOUT), else return true */
-	return !niso_timeout;
+	return niso_supported;
 }
 
 static int m_can_dev_setup(struct m_can_classdev *cdev)
@@ -1694,8 +1708,12 @@ static int m_can_dev_setup(struct m_can_classdev *cdev)
 		return -EINVAL;
 	}
 
-	if (cdev->ops->init)
-		cdev->ops->init(cdev);
+	/* Forcing standby mode should be redunant, as the chip should be in
+	 * standby after a reset. Write the INIT bit anyways, should the chip
+	 * be configured by previous stage.
+	 */
+	if (!m_can_cccr_update_bits(cdev, CCCR_INIT, CCCR_INIT))
+		return -EBUSY;
 
 	return 0;
 }
@@ -1708,7 +1726,8 @@ static void m_can_stop(struct net_device *dev)
 	m_can_disable_all_interrupts(cdev);
 
 	/* Set init mode to disengage from the network */
-	m_can_config_endisable(cdev, true);
+	if (!m_can_cccr_update_bits(cdev, CCCR_INIT, CCCR_INIT))
+		netdev_err(dev, "failed to enter standby mode\n");
 
 	/* set the state as STOPPED */
 	cdev->can.state = CAN_STATE_STOPPED;
diff --git a/drivers/net/can/m_can/tcan4x5x-core.c b/drivers/net/can/m_can/tcan4x5x-core.c
index a42600dac70d..d723206ac7c9 100644
--- a/drivers/net/can/m_can/tcan4x5x-core.c
+++ b/drivers/net/can/m_can/tcan4x5x-core.c
@@ -453,10 +453,17 @@ static int tcan4x5x_can_probe(struct spi_device *spi)
 		goto out_power;
 	}
 
-	ret = tcan4x5x_init(mcan_class);
+	tcan4x5x_check_wake(priv);
+
+	ret = tcan4x5x_write_tcan_reg(mcan_class, TCAN4X5X_INT_EN, 0);
 	if (ret) {
-		dev_err(&spi->dev, "tcan initialization failed %pe\n",
-			ERR_PTR(ret));
+		dev_err(&spi->dev, "Disabling interrupts failed %pe\n", ERR_PTR(ret));
+		goto out_power;
+	}
+
+	ret = tcan4x5x_clear_interrupts(mcan_class);
+	if (ret) {
+		dev_err(&spi->dev, "Clearing interrupts failed %pe\n", ERR_PTR(ret));
 		goto out_power;
 	}
 
-- 
2.44.0