From: Alex Elder <elder@linaro.org>
To: subashab@codeaurora.org, stranche@codeaurora.org,
davem@davemloft.net, kuba@kernel.org
Cc: sharathv@codeaurora.org, bjorn.andersson@linaro.org,
evgreen@chromium.org, cpratapa@codeaurora.org,
David.Laight@ACULAB.COM, olteanv@gmail.com, elder@kernel.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH net-next v4 4/6] net: qualcomm: rmnet: use masks instead of C bit-fields
Date: Mon, 15 Mar 2021 08:34:53 -0500 [thread overview]
Message-ID: <20210315133455.1576188-5-elder@linaro.org> (raw)
In-Reply-To: <20210315133455.1576188-1-elder@linaro.org>
The actual layout of bits defined in C bit-fields (e.g. int foo : 3)
is implementation-defined. Structures defined in <linux/if_rmnet.h>
address this by specifying all bit-fields twice, to cover two
possible layouts.
I think this pattern is repetitive and noisy, and I find the whole
notion of compiler "bitfield endianness" to be non-intuitive.
Stop using C bit-fields for the command/data flag and the pad length
fields in the rmnet_map structure, and define a single-byte flags
field instead. Define a mask for the single bit "command" flag,
and another mask for the encoded pad length. The content of both
fields can be accessed using a simple bitwise AND operation.
Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---
v4: - Don't use u8_get_bits() to access the pad length
- Added BUILD_BUG_ON() to ensure field width is adequate
v3: - Use BIT(x) and don't use u8_get_bits() for the command flag
.../ethernet/qualcomm/rmnet/rmnet_handlers.c | 4 ++--
.../ethernet/qualcomm/rmnet/rmnet_map_data.c | 4 +++-
include/linux/if_rmnet.h | 23 ++++++++-----------
3 files changed, 15 insertions(+), 16 deletions(-)
diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
index 2a6b2a609884c..0be5ac7ab2617 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
@@ -61,7 +61,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,
u16 len, pad;
u8 mux_id;
- if (map_header->cd_bit) {
+ if (map_header->flags & MAP_CMD_FLAG) {
/* Packet contains a MAP command (not data) */
if (port->data_format & RMNET_FLAGS_INGRESS_MAP_COMMANDS)
return rmnet_map_command(skb, port);
@@ -70,7 +70,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,
}
mux_id = map_header->mux_id;
- pad = map_header->pad_len;
+ pad = map_header->flags & MAP_PAD_LEN_MASK;
len = ntohs(map_header->pkt_len) - pad;
if (mux_id >= RMNET_MAX_LOGICAL_EP)
diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index fd55269c2ce3c..3c3307949db00 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -286,6 +286,7 @@ struct rmnet_map_header *rmnet_map_add_map_header(struct sk_buff *skb,
return map_header;
}
+ BUILD_BUG_ON(MAP_PAD_LEN_MASK < 3);
padding = ALIGN(map_datalen, 4) - map_datalen;
if (padding == 0)
@@ -299,7 +300,8 @@ struct rmnet_map_header *rmnet_map_add_map_header(struct sk_buff *skb,
done:
map_header->pkt_len = htons(map_datalen + padding);
- map_header->pad_len = padding & 0x3F;
+ /* This is a data packet, so the CMD bit is 0 */
+ map_header->flags = padding & MAP_PAD_LEN_MASK;
return map_header;
}
diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index 8c7845baf3837..a02f0a3df1d9a 100644
--- a/include/linux/if_rmnet.h
+++ b/include/linux/if_rmnet.h
@@ -6,21 +6,18 @@
#define _LINUX_IF_RMNET_H_
struct rmnet_map_header {
-#if defined(__LITTLE_ENDIAN_BITFIELD)
- u8 pad_len:6;
- u8 reserved_bit:1;
- u8 cd_bit:1;
-#elif defined (__BIG_ENDIAN_BITFIELD)
- u8 cd_bit:1;
- u8 reserved_bit:1;
- u8 pad_len:6;
-#else
-#error "Please fix <asm/byteorder.h>"
-#endif
- u8 mux_id;
- __be16 pkt_len;
+ u8 flags; /* MAP_CMD_FLAG, MAP_PAD_LEN_MASK */
+ u8 mux_id;
+ __be16 pkt_len; /* Length of packet, including pad */
} __aligned(1);
+/* rmnet_map_header flags field:
+ * PAD_LEN: number of pad bytes following packet data
+ * CMD: 1 = packet contains a MAP command; 0 = packet contains data
+ */
+#define MAP_PAD_LEN_MASK GENMASK(5, 0)
+#define MAP_CMD_FLAG BIT(7)
+
struct rmnet_map_dl_csum_trailer {
u8 reserved1;
#if defined(__LITTLE_ENDIAN_BITFIELD)
--
2.27.0
next prev parent reply other threads:[~2021-03-15 13:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 13:34 [PATCH net-next v4 0/6] net: qualcomm: rmnet: stop using C bit-fields Alex Elder
2021-03-15 13:34 ` [PATCH net-next v4 1/6] net: qualcomm: rmnet: mark trailer field endianness Alex Elder
2021-03-15 13:34 ` [PATCH net-next v4 2/6] net: qualcomm: rmnet: simplify some byte order logic Alex Elder
2021-03-15 16:02 ` Alexander Duyck
2021-03-15 17:12 ` Alex Elder
2021-03-15 13:34 ` [PATCH net-next v4 3/6] net: qualcomm: rmnet: kill RMNET_MAP_GET_*() accessor macros Alex Elder
2021-03-15 13:34 ` Alex Elder [this message]
2021-03-15 13:34 ` [PATCH net-next v4 5/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum trailer Alex Elder
2021-03-15 13:34 ` [PATCH net-next v4 6/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header Alex Elder
2021-03-15 16:12 ` [PATCH net-next v4 0/6] net: qualcomm: rmnet: stop using C bit-fields Alexander Duyck
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