net: moxa: get rid of asymmetry in DMA mapping/unmapping

Since priv->rx_mapping[i] is maped in moxart_mac_open(), we
should unmap it from moxart_mac_stop(). Fixes 2 warnings.

1. During error unwinding in moxart_mac_probe(): "goto init_fail;",
then moxart_mac_free_memory() calls dma_unmap_single() with
priv->rx_mapping[i] pointers zeroed.

WARNING: CPU: 0 PID: 1 at kernel/dma/debug.c:963 check_unmap+0x704/0x980
DMA-API: moxart-ethernet 92000000.mac: device driver tries to free DMA memory it has not allocated [device address=0x0000000000000000] [size=1600 bytes]
CPU: 0 PID: 1 Comm: swapper Not tainted 5.19.0+ #60
Hardware name: Generic DT based system
 unwind_backtrace from show_stack+0x10/0x14
 show_stack from dump_stack_lvl+0x34/0x44
 dump_stack_lvl from __warn+0xbc/0x1f0
 __warn from warn_slowpath_fmt+0x94/0xc8
 warn_slowpath_fmt from check_unmap+0x704/0x980
 check_unmap from debug_dma_unmap_page+0x8c/0x9c
 debug_dma_unmap_page from moxart_mac_free_memory+0x3c/0xa8
 moxart_mac_free_memory from moxart_mac_probe+0x190/0x218
 moxart_mac_probe from platform_probe+0x48/0x88
 platform_probe from really_probe+0xc0/0x2e4

2. After commands:
 ip link set dev eth0 down
 ip link set dev eth0 up

WARNING: CPU: 0 PID: 55 at kernel/dma/debug.c:570 add_dma_entry+0x204/0x2ec
DMA-API: moxart-ethernet 92000000.mac: cacheline tracking EEXIST, overlapping mappings aren't supported
CPU: 0 PID: 55 Comm: ip Not tainted 5.19.0+ #57
Hardware name: Generic DT based system
 unwind_backtrace from show_stack+0x10/0x14
 show_stack from dump_stack_lvl+0x34/0x44
 dump_stack_lvl from __warn+0xbc/0x1f0
 __warn from warn_slowpath_fmt+0x94/0xc8
 warn_slowpath_fmt from add_dma_entry+0x204/0x2ec
 add_dma_entry from dma_map_page_attrs+0x110/0x328
 dma_map_page_attrs from moxart_mac_open+0x134/0x320
 moxart_mac_open from __dev_open+0x11c/0x1ec
 __dev_open from __dev_change_flags+0x194/0x22c
 __dev_change_flags from dev_change_flags+0x14/0x44
 dev_change_flags from devinet_ioctl+0x6d4/0x93c
 devinet_ioctl from inet_ioctl+0x1ac/0x25c

v1 -> v2:
Extraneous change removed.

Fixes: 6c821bd ("net: Add MOXA ART SoCs ethernet driver")
Signed-off-by: Sergei Antonov <saproj@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220819110519.1230877-1-saproj@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/moxa/moxart_ether.c

@@ -71,11 +71,6 @@ static int moxart_set_mac_address(struct net_device *ndev, void *addr)
 static void moxart_mac_free_memory(struct net_device *ndev)
 {
 	struct moxart_mac_priv_t *priv = netdev_priv(ndev);
-	int i;
-
-	for (i = 0; i < RX_DESC_NUM; i++)
-		dma_unmap_single(&priv->pdev->dev, priv->rx_mapping[i],
-				 priv->rx_buf_size, DMA_FROM_DEVICE);
 
 	if (priv->tx_desc_base)
 		dma_free_coherent(&priv->pdev->dev,
@@ -187,6 +182,7 @@ static int moxart_mac_open(struct net_device *ndev)
 static int moxart_mac_stop(struct net_device *ndev)
 {
 	struct moxart_mac_priv_t *priv = netdev_priv(ndev);
+	int i;
 
 	napi_disable(&priv->napi);
 
@@ -198,6 +194,11 @@ static int moxart_mac_stop(struct net_device *ndev)
 	/* disable all functions */
 	writel(0, priv->base + REG_MAC_CTRL);
 
+	/* unmap areas mapped in moxart_mac_setup_desc_ring() */
+	for (i = 0; i < RX_DESC_NUM; i++)
+		dma_unmap_single(&priv->pdev->dev, priv->rx_mapping[i],
+				 priv->rx_buf_size, DMA_FROM_DEVICE);
+
 	return 0;
 }