linux-kernel - [PATCH net-next v4 6/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

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Date:   Mon, 15 Mar 2021 08:34:55 -0500
From:   Alex Elder <elder@...aro.org>
To:     subashab@...eaurora.org, stranche@...eaurora.org,
        davem@...emloft.net, kuba@...nel.org
Cc:     sharathv@...eaurora.org, bjorn.andersson@...aro.org,
        evgreen@...omium.org, cpratapa@...eaurora.org,
        David.Laight@...LAB.COM, olteanv@...il.com, elder@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net-next v4 6/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

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 masks to encode or get values within it.  The content of
these fields can be accessed using simple bitwise AND and OR
operations on the (host byte order) value of the new structure
member.

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@...aro.org>
---
v4: - Don't use u16_get_bits() to access the checksum field offset
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 3df23365497c4..bdb6ab6dad83d 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -197,23 +197,19 @@ 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 |= skb->csum_offset & MAP_CSUM_UL_OFFSET_MASK;
 
-	/* Changing remaining fields to network order */
-	hdr++;
-	*hdr = htons((__force u16)*hdr);
+	ul_header->csum_info = htons(val);
 
 	skb->ip_summed = CHECKSUM_NONE;
 
@@ -240,24 +236,19 @@ 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 |= skb->csum_offset & MAP_CSUM_UL_OFFSET_MASK;
 
-	/* 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 941997df9e088..4efb537f57f31 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_* */
 } __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_MASK		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