can: tcan4x5x: tcan4x5x_init(): fix initialization - clear MRAM before entering Normal Mode

This patch prevents a potentially destructive race condition. The
device is fully operational on the bus after entering Normal Mode, so
zeroing the MRAM after entering this mode may lead to loss of
information, e.g. new received messages.

This patch fixes the problem by first initializing the MRAM, then
bringing the device into Normale Mode.

Fixes: 5443c226 ("can: tcan4x5x: Add tcan4x5x driver to the kernel")
Link: https://lore.kernel.org/r/20210226163440.313628-1-torin@maxiluxsystems.comSuggested-by: NMarc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: NTorin Cooper-Bennun <torin@maxiluxsystems.com>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/tcan4x5x-core.c

@@ -237,14 +237,14 @@ static int tcan4x5x_init(struct m_can_classdev *cdev)
 	if (ret)
 		return ret;
 
+	/* Zero out the MCAN buffers */
+	m_can_init_ram(cdev);
+
 	ret = regmap_update_bits(tcan4x5x->regmap, TCAN4X5X_CONFIG,
 				 TCAN4X5X_MODE_SEL_MASK, TCAN4X5X_MODE_NORMAL);
 	if (ret)
 		return ret;
 
-	/* Zero out the MCAN buffers */
-	m_can_init_ram(cdev);
-
 	return ret;
 }