[PATCH v4 1/2] can: m_can: set init flag earlier in probe

[Matthias Schiffer]

While an m_can controller usually already has the init flag from a
hardware reset, no such reset happens on the integrated m_can_pci of the
Intel Elkhart Lake. If the CAN controller is found in an active state,
m_can_dev_setup() would fail because m_can_niso_supported() calls
m_can_cccr_update_bits(), which refuses to modify any other configuration
bits when CCCR_INIT is not set.

To avoid this issue, set CCCR_INIT before attempting to modify any other
configuration flags.

Fixes: cd5a46ce6fa6 ("can: m_can: don't enable transceiver when probing")
Signed-off-by: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>
Reviewed-by: Markus Schneider-Pargmann <msp@xxxxxxxxxxxx>
---

v2: no changes
v3: updated comment to mention Elkhart Lake
v4: added Reviewed-by

 drivers/net/can/m_can/m_can.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index 012c3d22b01dd..c85ac1b15f723 100644
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -1681,6 +1681,14 @@ static int m_can_dev_setup(struct m_can_classdev *cdev)
 		return -EINVAL;
 	}
 
+	/* Write the INIT bit, in case no hardware reset has happened before
+	 * the probe (for example, it was observed that the Intel Elkhart Lake
+	 * SoCs do not properly reset the CAN controllers on reboot)
+	 */
+	err = m_can_cccr_update_bits(cdev, CCCR_INIT, CCCR_INIT);
+	if (err)
+		return err;
+
 	if (!cdev->is_peripheral)
 		netif_napi_add(dev, &cdev->napi, m_can_poll);
 
@@ -1732,11 +1740,7 @@ static int m_can_dev_setup(struct m_can_classdev *cdev)
 		return -EINVAL;
 	}
 
-	/* Forcing standby mode should be redundant, as the chip should be in
-	 * standby after a reset. Write the INIT bit anyways, should the chip
-	 * be configured by previous stage.
-	 */
-	return m_can_cccr_update_bits(cdev, CCCR_INIT, CCCR_INIT);
+	return 0;
 }
 
 static void m_can_stop(struct net_device *dev)
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