can: peak_canfd: rearrange the way resources are released

This patch improves the sequence the resources are released by, first,

- disabling the IRQ in the controller, then by
- resetting the DMA logic, and finally, by
- adding a read cycle to ensure that the above commands have been received

before freeing the system interrupt.
Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/peak_canfd/peak_pciefd_main.c

@@ -488,13 +488,16 @@ static int pciefd_post_cmd(struct peak_canfd_priv *ucan)
 
 		/* controller now in reset mode: */
 
+		/* disable IRQ for this CAN */
+		pciefd_can_writereg(priv, CANFD_CTL_IEN_BIT,
+				    PCIEFD_REG_CAN_RX_CTL_CLR);
+
 		/* stop and reset DMA addresses in Tx/Rx engines */
 		pciefd_can_clear_tx_dma(priv);
 		pciefd_can_clear_rx_dma(priv);
 
-		/* disable IRQ for this CAN */
-		pciefd_can_writereg(priv, CANFD_CTL_IEN_BIT,
-				    PCIEFD_REG_CAN_RX_CTL_CLR);
+		/* wait for above commands to complete (read cycle) */
+		(void)pciefd_sys_readreg(priv->board, PCIEFD_REG_SYS_VER1);
 
 		free_irq(priv->ucan.ndev->irq, priv);