can: mcp251xfd: fix detection of mcp251863

In commit c6f2a617 ("can: mcp251xfd: add support for mcp251863")
support for the mcp251863 was added. However it was not taken into
account that the auto detection of the chip model cannot distinguish
between mcp2518fd and mcp251863 and would lead to a warning message if
the firmware specifies a mcp251863.

Fix auto detection: If a mcp2518fd compatible chip is found, keep the
mcp251863 if specified by firmware, use mcp2518fd instead.

Link: https://lore.kernel.org/all/20220706064835.1848864-1-mkl@pengutronix.de
Fixes: c6f2a617 ("can: mcp251xfd: add support for mcp251863")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

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

@@ -1690,8 +1690,8 @@ static int mcp251xfd_register_chip_detect(struct mcp251xfd_priv *priv)
 	u32 osc;
 	int err;
 
-	/* The OSC_LPMEN is only supported on MCP2518FD, so use it to
-	 * autodetect the model.
+	/* The OSC_LPMEN is only supported on MCP2518FD and MCP251863,
+	 * so use it to autodetect the model.
 	 */
 	err = regmap_update_bits(priv->map_reg, MCP251XFD_REG_OSC,
 				 MCP251XFD_REG_OSC_LPMEN,
@@ -1703,10 +1703,18 @@ static int mcp251xfd_register_chip_detect(struct mcp251xfd_priv *priv)
 	if (err)
 		return err;
 
-	if (osc & MCP251XFD_REG_OSC_LPMEN)
-		devtype_data = &mcp251xfd_devtype_data_mcp2518fd;
-	else
+	if (osc & MCP251XFD_REG_OSC_LPMEN) {
+		/* We cannot distinguish between MCP2518FD and
+		 * MCP251863. If firmware specifies MCP251863, keep
+		 * it, otherwise set to MCP2518FD.
+		 */
+		if (mcp251xfd_is_251863(priv))
+			devtype_data = &mcp251xfd_devtype_data_mcp251863;
+		else
+			devtype_data = &mcp251xfd_devtype_data_mcp2518fd;
+	} else {
 		devtype_data = &mcp251xfd_devtype_data_mcp2517fd;
+	}
 
 	if (!mcp251xfd_is_251XFD(priv) &&
 	    priv->devtype_data.model != devtype_data->model) {