[PATCH net-next v3 6/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

[Alex Elder]

Replace the use of C bit-fields in the rmnet_map_ul_csum_header
structure with a single two-byte (big endian) structure member,
and use bit or field masks to encode or get values within it.

Previously rmnet_map_ipv4_ul_csum_header() would update C bit-field
values in host byte order, then forcibly fix their byte order using
a combination of byte swap operations and types.

Instead, just compute the value that needs to go into the new
structure member and save it with a simple byte-order conversion.

Make similar simplifications in rmnet_map_ipv6_ul_csum_header().

Finally, in rmnet_map_checksum_uplink_packet() a set of assignments
zeroes every field in the upload checksum header.  Replace that with
a single memset() operation.

Signed-off-by: Alex Elder <elder@xxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
---
v3: Use BIT(x) and don't use u16_get_bits() for single-bit flags
v2: Fixed to use u16_encode_bits() instead of be16_encode_bits().

 .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 34 ++++++-------------
 include/linux/if_rmnet.h                      | 21 ++++++------
 2 files changed, 21 insertions(+), 34 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index 72dbbe2c27bd7..1ddc3440c8b48 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -198,23 +198,19 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,
 			      struct rmnet_map_ul_csum_header *ul_header,
 			      struct sk_buff *skb)
 {
-	__be16 *hdr = (__be16 *)ul_header;
 	struct iphdr *ip4h = iphdr;
 	u16 offset;
+	u16 val;
 
 	offset = skb_transport_header(skb) - (unsigned char *)iphdr;
 	ul_header->csum_start_offset = htons(offset);
 
-	ul_header->csum_insert_offset = skb->csum_offset;
-	ul_header->csum_enabled = 1;
+	val = MAP_CSUM_UL_ENABLED_FLAG;
 	if (ip4h->protocol == IPPROTO_UDP)
-		ul_header->udp_ind = 1;
-	else
-		ul_header->udp_ind = 0;
+		val |= MAP_CSUM_UL_UDP_FLAG;
+	val |= u16_encode_bits(skb->csum_offset, MAP_CSUM_UL_OFFSET_FMASK);
 
-	/* Changing remaining fields to network order */
-	hdr++;
-	*hdr = htons((__force u16)*hdr);
+	ul_header->csum_info = htons(val);
 
 	skb->ip_summed = CHECKSUM_NONE;
 
@@ -241,24 +237,19 @@ rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
 			      struct rmnet_map_ul_csum_header *ul_header,
 			      struct sk_buff *skb)
 {
-	__be16 *hdr = (__be16 *)ul_header;
 	struct ipv6hdr *ip6h = ip6hdr;
 	u16 offset;
+	u16 val;
 
 	offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
 	ul_header->csum_start_offset = htons(offset);
 
-	ul_header->csum_insert_offset = skb->csum_offset;
-	ul_header->csum_enabled = 1;
-
+	val = MAP_CSUM_UL_ENABLED_FLAG;
 	if (ip6h->nexthdr == IPPROTO_UDP)
-		ul_header->udp_ind = 1;
-	else
-		ul_header->udp_ind = 0;
+		val |= MAP_CSUM_UL_UDP_FLAG;
+	val |= u16_encode_bits(skb->csum_offset, MAP_CSUM_UL_OFFSET_FMASK);
 
-	/* Changing remaining fields to network order */
-	hdr++;
-	*hdr = htons((__force u16)*hdr);
+	ul_header->csum_info = htons(val);
 
 	skb->ip_summed = CHECKSUM_NONE;
 
@@ -425,10 +416,7 @@ void rmnet_map_checksum_uplink_packet(struct sk_buff *skb,
 	}
 
 sw_csum:
-	ul_header->csum_start_offset = 0;
-	ul_header->csum_insert_offset = 0;
-	ul_header->csum_enabled = 0;
-	ul_header->udp_ind = 0;
+	memset(ul_header, 0, sizeof(*ul_header));
 
 	priv->stats.csum_sw++;
 }
diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index a848bb2e0dad0..141754d0078cc 100644
--- a/include/linux/if_rmnet.h
+++ b/include/linux/if_rmnet.h
@@ -33,17 +33,16 @@ struct rmnet_map_dl_csum_trailer {
 
 struct rmnet_map_ul_csum_header {
 	__be16 csum_start_offset;
-#if defined(__LITTLE_ENDIAN_BITFIELD)
-	u16 csum_insert_offset:14;
-	u16 udp_ind:1;
-	u16 csum_enabled:1;
-#elif defined (__BIG_ENDIAN_BITFIELD)
-	u16 csum_enabled:1;
-	u16 udp_ind:1;
-	u16 csum_insert_offset:14;
-#else
-#error	"Please fix <asm/byteorder.h>"
-#endif
+	__be16 csum_info;		/* MAP_CSUM_UL_*_FMASK */
 } __aligned(1);
 
+/* csum_info field:
+ *  OFFSET:	where (offset in bytes) to insert computed checksum
+ *  UDP:	1 = UDP checksum (zero checkum means no checksum)
+ *  ENABLED:	1 = checksum computation requested
+ */
+#define MAP_CSUM_UL_OFFSET_FMASK	GENMASK(13, 0)
+#define MAP_CSUM_UL_UDP_FLAG		BIT(14)
+#define MAP_CSUM_UL_ENABLED_FLAG	BIT(15)
+
 #endif /* !(_LINUX_IF_RMNET_H_) */
-- 
2.27.0