diff mbox series

[net-next,4/6] net: qualcomm: rmnet: use field masks instead of C bit-fields

Message ID 20210304223431.15045-5-elder@linaro.org
State Superseded
Headers show
Series net: qualcomm: rmnet: stop using C bit-fields | expand

Commit Message

Alex Elder March 4, 2021, 10:34 p.m. UTC
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.  Instead, define a single-byte
flags field, and use the functions defined in <linux/bitfield.h>,
along with field mask constants to extract or assign values within
that field.

Signed-off-by: Alex Elder <elder@linaro.org>

---
 .../ethernet/qualcomm/rmnet/rmnet_handlers.c  |  5 ++--
 .../ethernet/qualcomm/rmnet/rmnet_map_data.c  |  4 +++-
 include/linux/if_rmnet.h                      | 23 ++++++++-----------
 3 files changed, 16 insertions(+), 16 deletions(-)

-- 
2.20.1

Comments

Bjorn Andersson March 5, 2021, 4:50 a.m. UTC | #1
On Thu 04 Mar 16:34 CST 2021, Alex Elder wrote:

> 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.  Instead, define a single-byte

> flags field, and use the functions defined in <linux/bitfield.h>,

> along with field mask constants to extract or assign values within

> that field.

> 


Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>


Regards,
Bjorn

> Signed-off-by: Alex Elder <elder@linaro.org>

> ---

>  .../ethernet/qualcomm/rmnet/rmnet_handlers.c  |  5 ++--

>  .../ethernet/qualcomm/rmnet/rmnet_map_data.c  |  4 +++-

>  include/linux/if_rmnet.h                      | 23 ++++++++-----------

>  3 files changed, 16 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..30f8e2f02696b 100644

> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c

> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c

> @@ -4,6 +4,7 @@

>   * RMNET Data ingress/egress handler

>   */

>  

> +#include <linux/bitfield.h>

>  #include <linux/netdevice.h>

>  #include <linux/netdev_features.h>

>  #include <linux/if_arp.h>

> @@ -61,7 +62,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,

>  	u16 len, pad;

>  	u8 mux_id;

>  

> -	if (map_header->cd_bit) {

> +	if (u8_get_bits(map_header->flags, MAP_CMD_FMASK)) {

>  		/* Packet contains a MAP command (not data) */

>  		if (port->data_format & RMNET_FLAGS_INGRESS_MAP_COMMANDS)

>  			return rmnet_map_command(skb, port);

> @@ -70,7 +71,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,

>  	}

>  

>  	mux_id = map_header->mux_id;

> -	pad = map_header->pad_len;

> +	pad = u8_get_bits(map_header->flags, MAP_PAD_LEN_FMASK);

>  	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..3291f252d81b0 100644

> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

> @@ -4,6 +4,7 @@

>   * RMNET Data MAP protocol

>   */

>  

> +#include <linux/bitfield.h>

>  #include <linux/netdevice.h>

>  #include <linux/ip.h>

>  #include <linux/ipv6.h>

> @@ -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 = u8_encode_bits(padding, MAP_PAD_LEN_FMASK);

>  

>  	return map_header;

>  }

> diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h

> index 8c7845baf3837..4824c6328a82c 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_*_FMASK */

> +	u8 mux_id;

> +	__be16 pkt_len;			/* Length of packet, including pad */

>  }  __aligned(1);

>  

> +/* rmnet_map_header flags field:

> + *  CMD:	1 = packet contains a MAP command; 0 = packet contains data

> + *  PAD_LEN:	number of pad bytes following packet data

> + */

> +#define MAP_CMD_FMASK			GENMASK(7, 7)

> +#define MAP_PAD_LEN_FMASK		GENMASK(5, 0)

> +

>  struct rmnet_map_dl_csum_trailer {

>  	u8  reserved1;

>  #if defined(__LITTLE_ENDIAN_BITFIELD)

> -- 

> 2.20.1

>
diff mbox series

Patch

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
index 2a6b2a609884c..30f8e2f02696b 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
@@ -4,6 +4,7 @@ 
  * RMNET Data ingress/egress handler
  */
 
+#include <linux/bitfield.h>
 #include <linux/netdevice.h>
 #include <linux/netdev_features.h>
 #include <linux/if_arp.h>
@@ -61,7 +62,7 @@  __rmnet_map_ingress_handler(struct sk_buff *skb,
 	u16 len, pad;
 	u8 mux_id;
 
-	if (map_header->cd_bit) {
+	if (u8_get_bits(map_header->flags, MAP_CMD_FMASK)) {
 		/* Packet contains a MAP command (not data) */
 		if (port->data_format & RMNET_FLAGS_INGRESS_MAP_COMMANDS)
 			return rmnet_map_command(skb, port);
@@ -70,7 +71,7 @@  __rmnet_map_ingress_handler(struct sk_buff *skb,
 	}
 
 	mux_id = map_header->mux_id;
-	pad = map_header->pad_len;
+	pad = u8_get_bits(map_header->flags, MAP_PAD_LEN_FMASK);
 	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..3291f252d81b0 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -4,6 +4,7 @@ 
  * RMNET Data MAP protocol
  */
 
+#include <linux/bitfield.h>
 #include <linux/netdevice.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
@@ -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 = u8_encode_bits(padding, MAP_PAD_LEN_FMASK);
 
 	return map_header;
 }
diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index 8c7845baf3837..4824c6328a82c 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_*_FMASK */
+	u8 mux_id;
+	__be16 pkt_len;			/* Length of packet, including pad */
 }  __aligned(1);
 
+/* rmnet_map_header flags field:
+ *  CMD:	1 = packet contains a MAP command; 0 = packet contains data
+ *  PAD_LEN:	number of pad bytes following packet data
+ */
+#define MAP_CMD_FMASK			GENMASK(7, 7)
+#define MAP_PAD_LEN_FMASK		GENMASK(5, 0)
+
 struct rmnet_map_dl_csum_trailer {
 	u8  reserved1;
 #if defined(__LITTLE_ENDIAN_BITFIELD)